Ask the Experts: All Questions

Ask the Experts is one of our most popular destinations for healthcare professionals. Our experts provide clear, easy-to-understand answers to commonly asked questions about vaccines and their use.

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Results (1355)

No. ACIP does not recommend routinely checking a patient’s temperature or other vital signs before vaccination. Requiring these extra steps can be a barrier to immunization.

Last reviewed: August 29, 2022

If a provider suspects an invalid vaccination, including those from persons vaccinated outside the U.S., one of two approaches can be taken. Repeating the vaccinations is an acceptable option. Doing so is generally safe and avoids the need to obtain and interpret serologic tests. If avoiding unnecessary injections is desired, judicious use of serologic testing might be helpful in determining which immunizations are needed. This may be particularly helpful in determining tetanus and diphtheria antitoxin levels for children whose records indicate 3 or more doses of DTP or DTaP. This issue is discussed in detail in the ACIP’s “General Best Practice Guidelines for Immunization” chapter titled Special Situations, and summarized in Table 9-1, available at www.cdc.gov/vaccines/hcp/acip-recs/general-recs/special-situations.html.

Last reviewed: June 6, 2023

The CDC’s General Best Practice Guidelines for Immunization generally recommends that live parenterally or nasally administered vaccines not given on the same day should be separated by at least 28 days. Despite this general principle, limited data suggest that coadministration of yellow fever vaccine and MMR may diminish the immune response. The CDC travel health website recommends that yellow fever vaccine and other parenteral or nasal live vaccines should be separated by at least 30 days, if possible. If yellow fever vaccine and another injectable live-virus vaccine are not administered either simultaneously or at least 30 days apart, CDC advises that providers might consider measuring the patient’s neutralizing antibody response to vaccination before travel. CDC recommends contacting the state health department or the CDC Arboviral Disease Branch (970-221-6400) to discuss serologic testing. For details, see the 2024 Yellow Book section on spacing of vaccines and immunobiologics: wwwnc.cdc.gov/travel/yellowbook/2024/preparing/vaccination-and-immunoprophylaxis-general-principles#spacing.

Last reviewed: August 21, 2023

Immunize.org has developed several screening questionnaires for patient use. These include:

  • Do I Need Any Vaccinations Today? (adult vaccination assessment checklist)
  • Vaccinations for Adults—You’re never too old to get immunized!
  • Vaccinations Needed During Pregnancy
  • Vaccinations for Adults with Chronic Liver Disease or Infection
  • Vaccinations for Adults with Diabetes
  • Vaccinations for Adults with Heart Disease
  • Vaccinations for Adults with HIV Infection
  • Vaccinations for Adults with Lung Disease
  • Vaccinations for Adults without a Spleen
  • Vaccinations for Men Who Have Sex with Men
  • Should You Be Vaccinated Against Hepatitis B? A screening questionnaire for adults, and
  • Should You Be Vaccinated for Hepatitis A? A screening questionnaire for adults.

These handouts can be found at www.immunize.org/handouts/view-all.asp

In addition to these printed pieces, there are several interactive tools on CDC’s website. For children, go to www2a.cdc.gov/vaccines/childquiz/, and for adults, go to www2.cdc.gov/nip/adultImmSched/.

Last reviewed: November 5, 2023

Occupational infection with HPV is possible. Some HPV-associated conditions (including anogenital and oral warts, anogenital intraepithelial neoplasia, and recurrent respiratory papillomatosis) are treated with laser or electrosurgical procedures that could produce airborne particles. These procedures should be performed in an appropriately ventilated room using standard precautions and local exhaust ventilation. Workers in HPV research laboratories who handle wild-type viruses or “quasi virions” might be at risk of acquiring HPV from occupational exposures. In the laboratory setting, proper infection control should be instituted, including, at minimum, biosafety level 2. Whether HPV vaccination would be of benefit in these settings is unclear because no data exist on transmission risk or vaccine efficacy in this situation.

Last reviewed: March 2, 2024

Tdap vaccination status does not change the approach to evaluating postexposure prophylaxis when HCWs are exposed to pertussis. Tdap vaccines have an uncertain role in the prevention of transmission of pertussis and herd protection. Antipertussis antibody levels begin to decline precipitously after the first year following a single Tdap vaccination. Healthcare facilities should follow the post-exposure prophylaxis protocol for pertussis exposure recommended by CDC regardless of a HCW’s vaccination status (see www.cdc.gov/pertussis/php/postexposure-prophylaxis). HCW can either receive postexposure prophylaxis or be carefully monitored for 21 days after pertussis exposure. Health care personnel should be treated with antibiotics at the onset of signs and symptoms of pertussis and excluded from work for the first 5 days while receiving appropriate antibiotics. CDC supports targeting postexposure antibiotic use to people at high risk of developing severe pertussis, as well as people who will have close contact with others at high risk of developing severe pertussis.

Last reviewed: October 31, 2023

Information regarding influenza surveillance is available year-round from CDC. For an overview and link to CDC’s influenza surveillance systems, visit www.cdc.gov/fluview/. CDC publishes updated information weekly. In addition, periodic updates about influenza are published in MMWR. CDC also publishes respiratory virus surveillance information that integrates influenza, COVID-19 and RSV at www.cdc.gov/respiratory-viruses/data/index.html.

State and local health departments should be consulted regarding local access to public health influenza vaccination programs and information about state or local influenza activity. Contact state or local health officials to report influenza outbreaks and for guidance in outbreak response.

Last reviewed: August 11, 2024

As a general rule, infants or children who are more than 1 month or 1 dose behind schedule should be on an accelerated schedule, which means the intervals between doses should be reduced to the minimum allowable. Catch-up schedules for children ages 4 months through 18 years are included in Table 2 of each year’s recommended immunization schedule for children and adolescents, approved by the ACIP, CDC, and all other major professional organizations of healthcare providers who care for children. To review Table 2, go to www.cdc.gov/vaccines/hcp/imz-schedules/child-adolescent-age.html and open the current schedule for children and adolescents.

Last reviewed: June 6, 2023

CDC recommends that all people age 6 months or older should be vaccinated with a 2024–2025 Formula COVID-19 vaccine, as authorized or approved by FDA. There are three options: Moderna or Pfizer-BioNTech mRNA vaccine (both FDA-authorized beginning at age 6 months and FDA-licensed for age 12 years and older), or Novavax adjuvanted protein subunit vaccine (authorized for age 12 years or older). Most people age 5 years or older should receive a single dose of vaccine.

Certain people need, or have the option to receive, more than one 2024–2025 Formula COVID-19 vaccine dose:

  • If administering Novavax to a previously unvaccinated person age 12 years or older, administer a recommended 2-dose primary series, with doses 3-8 weeks apart.
  • Children younger than age 5 years are recommended to receive at least one 2024–2025 Formula mRNA vaccine dose. If not previously vaccinated, or incompletely vaccinated, they should complete a 2-dose (Moderna) or 3-dose (Pfizer-BioNTech) primary series, using the same brand for all doses. CDC recommends that children younger than age 5 years receive the same brand for all doses (also referred to as homologous doses), even after completing the primary series. If it is not feasible to administer the same brand for one of the following reasons, it is acceptable to use a different brand: the brand is unavailable at the clinic at the time of the vaccination visit; the previous brand is unknown; the child would not otherwise receive a recommended vaccine; or, the child cannot continue with the previous brand due to a contraindication.
  • Individuals who are moderately or severely immunocompromised and who have not already completed a 3-dose primary series, should complete a 3-dose primary vaccination series with the current 2024–2025 formulation. Use the same brand for all doses of the primary series, unless the brand is unavailable at the time of the clinic visit, the patient would otherwise choose not to complete the series, or the patient has a contraindication to vaccination with the original product. If the primary series is already complete, then a single dose of any age-appropriate 2024–2025 COVID-19 vaccine should be administered at least 2 months after the most recent dose of COVID-19 vaccine. Additional doses may be given, spaced at least 2 months apart, as determined by these individuals with their clinical care teams.

At this time, adults age 65 years and older who are not moderately or severely immunocompromised are recommended to receive only 1 dose of any 2024–2025 Formula COVID-19 vaccine. These adults are not currently recommended to receive a second dose 6 months after the first dose. ACIP will consider recommendations for revaccination in the future.

Last reviewed: August 31, 2024

No. Doses of rabies vaccine given in the gluteus should not be counted as valid and should be repeated. If repeating the invalid dose results in an interval between doses more than 3 days longer than the recommended interval, then you should perform a rabies serology 7–14 days after administration of the final dose in the series to ensure an adequate immune response to the series. For more information about rabies serology, see www.cdc.gov/rabies/php/laboratories/diagnostic.html.

Last reviewed: May 14, 2023

One pneumococcal polysaccharide vaccine (PPSV23, Pneumovax 23, Merck) and three pneumococcal conjugate vaccines (PCV15 [Vaxneuvance, Merck], PCV20 [Prevnar 20, Pfizer], and PCV21 [Capvaxive, Merck]) are FDA-licensed and recommended by CDC for use in the United States. PCV13 (Prevnar 13, Pfizer) is FDA-licensed and may still be available in some clinics. It is no longer routinely recommended; however, CDC guidance allows for its use as previously recommended in situations where PCV15, PCV20, or PCV21 is indicated but unavailable and the alternative is that the patient would not be vaccinated.

PPSV23 is licensed for age 2 years and older. It was first licensed in 1983. It is an option for use in series with PCV15 for children and adults ages 2 through 64 years with specified risk factors for pneumococcal disease depending on their prior pneumococcal vaccination history. A PCV15 + PPSV23 series also is recommended as an option for pneumococcal disease prevention in adults 50 years and older. Following the 2022 changes to the pneumococcal vaccination schedule for adults, PPSV23 is no longer recommended alone, however PPSV23 is recommended for adults following PCV15 vaccination. It is not recommended for people who have previously received a PCV20 or PCV21 vaccination.

PCV15 is licensed for people age 6 weeks and older. CDC recommends the use of PCV15 as an option for the routine vaccination of children younger than age 5 years and certain children 6 through 18 years who have conditions that put them at high risk of invasive pneumococcal disease. CDC recommends PCV15 in series with PPSV23 as an option for pneumococcal disease prevention in adults age 19 through 49 years who are at increased risk for invasive pneumococcal disease due to behavioral or medical risk factors and for adults age 50 or older. When used in adults, it is always recommended to be used as part of a vaccination series with PPSV23 typically given 1 year later (a minimum interval of 8 weeks may be considered for people with immunocompromising medical conditions, cochlear implant or cerebrospinal fluid leak).

PCV20 is licensed for people age 6 weeks and older. CDC recommends the use of PCV20 as an option for the routine vaccination of children younger than 5 years of age and certain children 6 through 18 years who have conditions that put them at high risk of invasive pneumococcal disease. CDC recommends it as an option for pneumococcal disease prevention in adults age 19 through 49 years who are at increased risk for invasive pneumococcal disease due to behavioral or medical risk factors and for adults age 50 or older. If PCV20 is given, no further pneumococcal vaccination is recommended.

PCV21 was first licensed and recommended for adults in June 2024. CDC recommends the use of PCV21 as a product option for any adult age 19 or older when a PCV vaccine is recommended. It is specifically designed for adults: it does not contain 10 serotypes contained in PCV20; instead, it contains 11 additional serotypes that cause disease in adults. As with PCV20, after it is administered, no further pneumococcal vaccine doses are recommended.

For details of recommendations for these vaccines, see Recommendations for Pneumococcal Vaccines Use in Children and Teens, www.immunize.org/wp-content/uploads/catg.d/p2016.pdf, or Standing Orders for Administering Pneumococcal Vaccines to Adults: www.immunize.org/wp-content/uploads/catg.d/p3075.pdf.

Last reviewed: November 13, 2024

The most current comprehensive recommendations from the Advisory Committee on Immunization Practices (ACIP) for meningococcal vaccines is available on the MMWR website at www.cdc.gov/mmwr/volumes/69/rr/pdfs/rr6909a1-H.pdf. This document replaces all previously published reports and policy notes.

ACIP recommendations for the use of MenABCWY (Penbraya) were published in the MMWR in April 2024 and are at www.cdc.gov/mmwr/volumes/73/wr/pdfs/mm7315a4-H.pdf.

Last reviewed: November 15, 2024

In June 2023, ACIP recommended that all adults (18 years and older) in the United States who are known or suspected to be unvaccinated or incompletely vaccinated against polio should complete a primary 3-dose vaccination series with IPV: 2 doses of IPV administered at an interval of 4–8 weeks; and a third dose should be administered 6–12 months after the second. Previously, ACIP did not recommend IPV vaccination of unvaccinated or incompletely vaccinated adults who lacked a specific increased risk for exposure to polio (e.g., due to travel). Most U.S. adults may be presumed to be vaccinated against polio unless there is a specific reason to believe otherwise (e.g., an adult whose parents were known to have refused vaccinations). Rates of polio vaccination among children in the United States have been extremely high for decades.

Last reviewed: July 23, 2023


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Last reviewed: December 6, 2023

For individuals with moderate to severe immunocompromise, CDC states that, beyond the primary series, additional doses of 2024–2025 Formula COVID-19 vaccine may be administered (with a minimum two-month interval) based on the clinical judgment of the individual’s healthcare provider and personal preference and circumstances.

The option to receive these additional doses is offered because vaccine effectiveness declines most rapidly in people with moderate to severe immunocompromise. Such people also have the highest risk of hospitalization with COVID-19 if infected. Although protection against severe disease is more durable than protection against milder illness, individuals in these groups may benefit from shorter intervals between doses.

Last reviewed: August 31, 2024

In June 2023, ACIP affirmed its longstanding recommendation that adults who received a primary series of trivalent OPV (tOPV) or IPV in any combination and who are at increased risk of poliovirus exposure may receive another dose of IPV. Available data do not indicate the need for more than a single lifetime booster dose with IPV for adults.

The following are examples of vaccinated adults at increased risk of exposure who may receive a single lifetime booster dose of IPV:

  • Travelers who are going to countries where polio is epidemic or endemic (see polio information for travelers at wwwnc.cdc.gov/travel/)
  • Laboratory and healthcare workers who handle specimens that might contain polioviruses
  • Healthcare workers or other caregivers who have close contact with a person who could be infected with poliovirus
Last reviewed: July 23, 2023

All children, beginning at age 12 months, as well as adults without other evidence of immunity should be vaccinated with 2 doses of varicella vaccine. Special consideration should be given to vaccinating adults who (1) have close contact with people at high risk for severe disease (e.g., healthcare workers and family contacts of immunocompromised people), or (2) are at high risk for exposure or transmission (e.g., teachers of young children; child care employees; residents and staff members of institutional settings, including correctional institutions; college students; military personnel; adolescents and adults living in households with children; non-pregnant women of childbearing age; and international travelers).

Last reviewed: May 16, 2023

The accelerated schedule should be used when the child is more than a month behind schedule, until you get them caught up. An accelerated schedule is acceptable as long as minimum ages and minimum intervals are observed for each dose. Once you have the child back on schedule, use the recommended ages and intervals on the childhood schedule. In this case you can give the child the first set of recommended vaccines at age 3 months and then bring him back at age 4 months and give the second set of vaccinations. At this point the child will be caught up and can return to the usual schedule. Be sure to educate the parents and talk to them about the importance of bringing the child back on time.

Last reviewed: June 6, 2023

There is usually very close agreement between vaccine package inserts and ACIP statements. The Food and Drug Administration (FDA) must approve the package insert, and requires documentation for all data and recommendations made in the insert. Occasionally, ACIP may use different data to formulate its recommendations, or try to add flexibility to its recommendations, which results in wording different than in the package insert. ACIP sometimes makes recommendations based on expert opinion and public health considerations. Published recommendations of ACIP should be considered equally as authoritative as those on the package insert.

Last reviewed: August 22, 2020

Syncope, also called fainting, is a temporary loss of consciousness as a result of decreased blood flow to the brain. The most common form of fainting is called “vasovagal” fainting. This type of fainting can be triggered by an event associated with pain or anxiety. Some people may experience jerking movements after fainting which are not seizures. Published literature reveals that about 3% of men and 3.5% of women report at least one episode of fainting during their lifetime.

Last reviewed: August 31, 2022

In May 2022, CDC published updated ACIP recommendations for rabies PrEP based on risk categories. All people in categories 1-4 should receive a 2-dose primary PrEP rabies vaccine series. People in categories 1-3 require additional long-term follow-up with periodic antibody titer checks and/or booster doses, depending on the category. See the table on pages 622-623 of the MMWR publication for details: www.cdc.gov/mmwr/volumes/71/wr/pdfs/mm7118a2-H.pdf.

In brief, the risk categories are as follows:

  • Risk category 1: elevated risk of unrecognized or recognized exposures, including unusual or high-risk exposures (e.g., laboratory or rabies vaccine production settings)
  • Risk category 2: elevated risk, exposures typically recognized but may be unrecognized (e.g., people who frequently interact with bats or collect suspected rabies samples)
  • Risk category 3: elevated risk, exposure nearly always recognized (e.g., veterinary workers, people who handle wildlife reservoir species, spelunkers [because of bats], and certain travelers who have increased risk and may have trouble obtaining safe post-exposure prophylaxis)
  • Risk category 4: same type of risk as category 3, but risk period is time-limited (no more than 3 years)
  • Risk category 5: low risk, typical person living in the United States (PrEP not recommended)
Last reviewed: May 14, 2023

Three monovalent Hib vaccines are available in the United States: PedvaxHIB (PRP-OMP, Merck), ActHIB (PRP-T, Sanofi) and Hiberix (PRP-T, GSK). These vaccines are composed of Hib purified polyribosylribitol phosphate (PRP) capsular polysaccharide chemically bound (conjugated) to a protein to enhance the quality of the immune response to PRP. All three vaccines are approved for infants in a 3- or 4-dose series (depending on brand).

Two combination vaccines containing Hib are currently available in the United States: Pentacel (DTaP-IPV/Hib, Sanofi) and Vaxelis (DTaP-IPV-Hib-HepB, MSP Company). Pentacel is licensed for use in children younger than age 5 years and contains Hib conjugate, DTaP, and inactivated polio vaccines; it is approved as a 4-dose series for infants at age 2, 4, 6, and 15 through 18 months, but it is not approved for use as the DTaP/IPV booster dose recommended at age 4 to 6 years. Vaxelis (DTaP-IPV-Hib-HepB, MSP Company) is licensed for use in children younger than age 5 years and is FDA-approved and recommended by CDC as a 3-dose primary series of Hib for infants at age 2, 4, and 6 months. Vaxelis is not approved for use as a Hib booster (4th) dose. Vaxelis contains the same PRP-OMP Hib antigen as PedvaxHIB, but in a reduced amount.

Last reviewed: July 31, 2022

Pediarix contains the vaccine components DTaP, IPV, and HepB. The primary series is 3 doses (0.5 mL) given intramuscularly at 2, 4, and 6 months of age. Pediarix is licensed by the Food and Drug Administration (FDA) for only the first 3 doses of the DTaP series. It should not be given to infants younger than 6 weeks of age or to children 7 years or older.

Last reviewed: July 15, 2023

No. If you turn off the freezer portion of a household-style combination refrigerator/freezer, the refrigerated compartment will not maintain the proper temperature.

Last reviewed: July 26, 2023

The two rotavirus vaccine products differ in composition and schedule of administration. RotaTeq was approved by the Food and Drug Administration (FDA) in 2006. It contains five reassortant rotaviruses developed from human and bovine parent rotavirus strains; 3 doses are given in the series. Rotarix was approved by the FDA in 2008 and contains an attenuated human rotavirus strain; 2 doses are given in the series.

Last reviewed: June 7, 2023

Ideally, you can arrange to have the cast cut to administer vaccines in the anterolateral thighs. If that option is not available, the gluteal region can be used if not covered by the cast. There are no other sites we recommend for vaccination; however, the inactivated polio vaccine could be given subcutaneously in either arm, if the child is large enough. Rotavirus vaccine is given orally and should be administered. If vaccines cannot be given for the 10 weeks, please advise the family to keep people with any illness away from the child until she has been vaccinated. More information see ACIP’s “General Best Practices Guidelines for Immunization”, available at www.cdc.gov/vaccines/hcp/acip-recs/general-recs/administration.html.

Last reviewed: December 28, 2022

A polysaccharide vaccine is a type of vaccine that is composed of long chains of sugar molecules, called polysaccharides, that resemble the surface of certain serotypes of pneumococcal bacteria in order to help the immune system mount a response.

A conjugate vaccine is a type of vaccine that joins a protein to an antigen (in the case of pneumococcal vaccines, the protein is connected to unique polysaccharides from the surface of each of the pneumococcal serotypes). The protein helps improve the quality of the immune system response to the vaccine compared to the response to an unconjugated polysaccharide.

Last reviewed: November 13, 2024

Recombinant zoster vaccine (RZV, Shingrix, GlaxoSmithKline) was licensed by the Food and Drug Administration (FDA) in October 2017. It is a subunit vaccine that contains recombinant varicella zoster virus (VZV) glycoprotein E in combination with a novel adjuvant (AS01B). Shingrix does not contain live VZV. It is FDA-approved and recommended by the Advisory Committee on Immunization Practices (ACIP) for all people 50 years and older and for adults age 19 years or older who are or will be immunodeficient or immunosuppressed because of disease or therapy. It has not been evaluated and is not approved for the prevention of primary varicella infection. Shingrix is administered as a 2-dose series by the intramuscular route. The second dose should be given 2 to 6 months after the first dose, with a minimum interval of 1 month (4 weeks) between doses.

Zoster vaccine live (ZVL, Zostavax, Merck) is a live attenuated vaccine that was licensed by the FDA in 2006 for adults age 50 and older and recommended by ACIP for people age 60 and older. Zostavax has been unavailable for use in the United States since November 18, 2020.

Last reviewed: March 9, 2022

In 2017, the Immunization Action Coalition revised its comprehensive 142-page guide titled Vaccinating Adults: A Step-by-Step Guide. The guide was written to assist medical practices to improve their adult vaccination services. Two of the chapters (7A and 7B) address financial considerations and provide guidance on how to obtain reimbursement for adult vaccines. The guide is available free of charge on the Immunize.org website at www.immunize.org/guide. In addition, the National Adult and Influenza Immunization Summit has created a web section on this topic at www.izsummitpartners.org/naiis-workgroups/access-provider-workgroup/coding-and-billing.

The Inflation Reduction Act of 2022, once fully enacted during 2023, will substantially reduce cost-related barriers to vaccination for adults. The law eliminates cost-sharing for ACIP-recommended vaccination of all adults covered by Medicaid and Medicaid expansion plans, as well as adults with Medicare Part D. It also provides for enhanced federal reimbursement for immunizing providers. Details about implementation are forthcoming at the time of this update.

Last reviewed: August 26, 2022

A “moderate or severe acute illness” is a precaution for administering any vaccine. A mild acute illness (e.g., diarrhea or mild upper-respiratory tract infection) with or without fever is not a precaution, and vaccines may be given. The concern in vaccinating someone with moderate or severe illness is that a fever following the vaccine could complicate management of the concurrent illness – it could be difficult to determine if the fever was from the vaccine or due to the concurrent illness. In deciding whether to vaccinate a patient with moderate or severe illness, the clinician needs to determine if deferring vaccination will increase the patient’s risk of vaccine-preventable diseases, as is the case if the patient is unlikely to return for vaccination or to seek vaccination elsewhere.

Last reviewed: August 29, 2022

No, Dengvaxia does not protect the recipient against yellow fever.

Last reviewed: February 16, 2022

Generally speaking, no. A person with laboratory evidence of resolved hepatitis B infection is considered immune. Vaccination of such individuals is not harmful but is not necessary.

Last reviewed: July 21, 2023

CDC recommends that all travelers to countries affected by wild (WPV) or circulating vaccine-derived poliovirus (cVDPV) be vaccinated fully against polio. Adults who were fully vaccinated during childhood may receive an additional (single) lifetime booster dose of polio vaccine.

WHO recommends that countries affected by wild poliovirus or cVDPV outbreaks require residents and long-term (4 weeks or more) visitors show proof of polio vaccination before leaving the country. These recommendations are regularly reviewed and updated. Visit CDC’s Travelers’ Health site for current details about country-specific requirements (wwwnc.cdc.gov/travel/).

Last reviewed: July 23, 2023

The most recent comprehensive ACIP recommendations for the use of MMR vaccine were published in 2013 and are available at www.cdc.gov/mmwr/pdf/rr/rr6204.pdf. CDC published the ACIP recommendations for the use of Priorix (GSK) brand of MMR vaccine on November 18, 2022, and they are available here: www.cdc.gov/mmwr/volumes/71/wr/pdfs/mm7146a1-H.pdf.

There is no difference in recommendations between Priorix and MMRII (Merck) brands of MMR vaccine. Priorix may be used in any situation where MMR vaccination is recommended. Despite minor differences in manufacturing (MMRII contains gelatin, Priorix does not) and approved route of administration (MMRII is approved for subcutaneous or intramuscular injection, Priorix is approved for subcutaneous injection only), the two vaccines may be considered functionally identical and interchangeable.

MMR vaccine is recommended routinely for all children at age 12 through 15 months, with a second dose at age 4 through 6 years. The second dose of MMR can be given as early as 4 weeks (28 days) after the first dose and be counted as a valid dose if both doses were given after the child’s first birthday. The second dose is not a booster, but rather is intended to produce immunity in the small number of people who fail to respond to the first dose.

Adults with no evidence of immunity should get 1 dose of MMR vaccine (evidence of immunity is defined as documented receipt of 1 dose of live measles virus-containing vaccine [or 2 doses, if high risk], laboratory evidence of immunity or laboratory confirmation of disease, or birth before 1957), unless the adult is in a high-risk group. Susceptible high-risk people need 2 doses of vaccine, given 4 weeks apart. High risk people include school-age children, healthcare personnel, international travelers, and students attending post-high school educational institutions.

Live-attenuated measles vaccine became available in the U.S. in 1963. An ineffective, inactivated measles vaccine was also available in the U.S. in 1963–1967. Combined MMR vaccine (MMRII, Merck) was licensed in 1971; Priorix (GSK) MMR vaccine was licensed and recommended in 2022. For people who previously received a dose of measles vaccine in 1963–1967 and are unsure which type of vaccine it was, or are sure it was inactivated measles vaccine, that dose should be considered invalid and the patient revaccinated as age- and risk-appropriate with MMR vaccine. At the discretion of the state public health department, anyone exposed to measles in an outbreak setting can receive an additional dose of MMR vaccine even if they are considered completely vaccinated for their age or risk status.

Last reviewed: June 19, 2023

Yes. TBE is caused by a flavivirus transmitted by ticks in certain regions of Asia and Europe. Most infections are asymptomatic, but it can cause meningitis and encephalitis. In August 2021, the FDA approved a TBE vaccine, Ticovac (by Pfizer), for people age 1 year or older. The dose for people age 16 years and older is 0.5mL, and for children and adolescents up to age 15 years is 0.25mL. The primary vaccination schedule includes 3 doses, and a booster dose can be given if ongoing exposure or re-exposure to TBE virus is expected. TBE vaccines are also available in many countries overseas where TBE virus is present. For more information from CDC about the TBE vaccine, visit www.cdc.gov/tick-borne-encephalitis/hcp/vaccine/index.html.

Last reviewed: August 21, 2023

Nonsexual HPV transmission is theoretically possible but has not been definitively demonstrated. This is mainly because HPV can’t be cultured, and DNA detection from the environment is difficult and likely prone to false negative results.

Last reviewed: March 2, 2024

MenACWY is recommended for these groups:

Routine vaccination of all children and teens, age 11 through 18 years: a single dose at age 11 or 12 years with a booster dose at age 16 years

Routine vaccination of people age 2 months or older at increased risk for meningococcal disease (the primary dosing schedule and booster dose interval varies by age and indication):

  • People with functional or anatomic asplenia
  • People who have persistent complement component deficiency (an immune system disorder) or who take a complement inhibitor (examples include eculizumab [Soliris] and ravulizumab [Ultomiris])
  • People who have HIV infection
  • People who are at risk during an outbreak caused by a vaccine serogroup
  • People age 2 months and older who reside in or travel to certain countries in sub-Saharan Africa as well as to other countries for which meningococcal vaccine is recommended (e.g., travel to Mecca, Saudi Arabia, for the annual Hajj)
  • Microbiologists who work with meningococcus bacterial isolates in a laboratory
  • First-year college students living in residence halls who are unvaccinated or undervaccinated; these students should receive a dose if they have not had a dose since turning 16 or if it has been more than 5 years since their previous dose
Last reviewed: November 15, 2024

MenB is routinely recommended for these groups:

  • People age 10 years and older who have functional or anatomic asplenia (including sickle cell disease)
  • People age 10 years and older who have persistent complement component deficiency (an immune system disorder) or who take a complement inhibitor (examples include eculizumab [Soliris, Alexion Pharmaceuticals] and ravulizumab [Ultomiris, Alexion Pharmaceuticals])
  • People age 10 years and older who are exposed during an outbreak caused by serogroup B
  • Microbiologists who work with meningococcal isolates in a laboratory

For adolescents and young adults not otherwise at increased risk for meningococcal B disease, ACIP recommends that a MenB series may be administered to people 16 through 23 years of age (preferred age 16 through 18 years) on the basis of shared clinical decision-making. The shared clinical decision-making recommendation allows the clinician and patient to decide together based upon the risks and benefits of vaccination for the individual patient.

Last reviewed: March 24, 2024

Recent Tdap vaccination does not affect PCR testing. PCR tests are used to detect DNA sequences of the Bordetella pertussis bacterium. PCR tests are very sensitive and could give a false positive result for other reasons. For more information on best practices when performing PCR testing for pertussis see www.cdc.gov/pertussis/php/pcr-bestpractices.

Last reviewed: October 31, 2023

The incidence of hepatitis A in the US increased more than 10-fold from 2015 to 2019, with over 18,800 cases reported to CDC in 2019. The number of reported cases declined by 47% to 9,952 in 2020. This number is an underestimate of the actual number of infections: CDC estimates that about 19,900 cases actually occurred in 2020.

Between 2012 and 2015 the number of reported hepatitis A infections ranged from approximately 1200 to 1800 cases every year. Beginning in 2016, large foodborne outbreaks led to an increase in the number of cases and sustained, large person-to-person outbreaks began, primarily driven by infections among unvaccinated people who use drugs and people experiencing homelessness and their contacts. Since then, persistent person-to-person outbreaks have led to substantial increases in hepatitis A infection, with 37 states reporting almost 45,000 cases over the 7 years between the beginning of the outbreaks in 2016 and June 2023. The rate of new cases has declined substantially since the peak in 2019. More information regarding ongoing multistate outbreaks can be found here: www.cdc.gov/hepatitis/outbreaks/ongoing-hepatitis-a.

Last reviewed: June 25, 2023

In May 2023, FDA licensed two RSV vaccines: RSVPreF3 (Arexvy, GSK) and RSVpreF (Abrysvo, Pfizer). A third RSV vaccine, mRNA RSV (mResvia, Moderna), was licensed by FDA in May 2024. All three vaccines are licensed for the prevention of RSV-associated lower respiratory tract disease (LRTD) in adults 60 age years and older in the United States. Arexvy is also licensed for use in adults age 50 through 59 years who are increased risk of RSV LRTD; however, ACIP has not yet made recommendations for its use in this age group. Only Abrysvo is licensed for use during pregnancy (during 32 through 36 weeks and 6 days’ gestation) for the prevention of RSV disease in infants.

Arexvy and Abrysvo are recombinant protein vaccines that contain the prefusion form of the spike protein found on the surface of the RSV virus. The mResvia mRNA vaccine contains mRNA that encodes the prefusion form of the RSV F glycoprotein. The mRNA vaccine temporarily enables some of the vaccine recipient’s own cells to produce the prefusion form of the spike protein, causing the immune system to respond by generating antibodies to it. Because none of these vaccines contain live virus, they cannot cause RSV illness.

The GSK vaccine, Arexvy, includes an AS01adjuvant, a chemical designed to enhance the immune response to vaccination. AS01 is the same adjuvant used in GSK’s recombinant zoster vaccine (Shingrix), but Arexvy contains half the amount of adjuvant as a dose of Shingrix. Abrysvo and mResvia vaccines do not contain an adjuvant.

For further information about the vaccines, see the FDA package inserts: Arexvy (www.fda.gov/media/167805/download); Abrysvo (www.fda.gov/media/168889/download); and mResvia (www.fda.gov/media/179005/download).

Last reviewed: August 25, 2024

Janssen (Johnson & Johnson) COVID-19 vaccine is no longer available for use in the United States. The last remaining doses expired May 7, 2023. People who received 1 or 2 Janssen COVID-19 Vaccine doses are recommended to receive one 2024–2025 Formula dose (Moderna, Pfizer-BioNTech, or Novavax).

Last reviewed: August 31, 2024

Yearly influenza vaccination continues to be recommended for everyone age 6 months and older. Changes relevant to clinical practice in the CDC’s published ACIP recommendations for influenza vaccination in the 2024-25 season are summarized below:

  • ACIP now recommends high-dose inactivated influenza vaccine (HD-IIV) or adjuvanted inactivated (aIIV) influenza vaccine (each licensed by FDA for people age 65 years or older) as acceptable options for influenza vaccination of solid organ transplant recipients age 18 through 64 years who are on immunosuppressive medication regimens. There is no preference for aIIV or HD-IIV over any other age-appropriate inactivated or recombinant influenza vaccine in this group.
  • The HD-IIV vaccine, which is now trivalent, is given at a dose of 0.5 mL (the previous dose for quadrivalent HD-IIV was 0.7 mL).
  • ACIP affirmed that everyone age 6 months and older who has an egg allergy should receive influenza vaccine. Any influenza vaccine (egg based or non-egg based) that is otherwise appropriate for the recipient’s age and health status may be used. ACIP updated its recommendation to state that egg allergy alone necessitates no additional safety measures for influenza vaccination beyond those recommended for any recipient of any vaccine, regardless of severity of previous reaction to egg. All vaccines should be administered in settings in which personnel and equipment needed for rapid recognition and treatment of acute hypersensitivity reactions are available.

The current ACIP recommendations for influenza vaccination are available here:  www.cdc.gov/acip-recs/hcp/vaccine-specific/flu.html.

Last reviewed: August 11, 2024


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Last reviewed: May 9, 2023


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Last reviewed: March 28, 2023

ACIP recommends annual vaccination for all people ages 6 months and older who do not have a contraindication to influenza vaccination.

Last reviewed: August 11, 2024

The Advisory Committee on Immunization Practices (ACIP) considers evidence of immunity to varicella to be:

  • Written documentation of 2 doses of varicella vaccine given no earlier than age 12 months with at least 4 weeks between doses.
  • U.S.-born before 1980*
  • A healthcare provider’s diagnosis of varicella or verification of history of varicella disease
  • History of herpes zoster, based on healthcare provider diagnosis or verification of disease history
  • Laboratory evidence of immunity or laboratory confirmation of disease

    *Note: Although there is only a very small chance of susceptibility, due to the potential for severe consequences from varicella infection, year of birth is not accepted as evidence of varicella immunity for healthcare personnel, immunosuppressed people, and pregnant people.

Last reviewed: May 16, 2023

Yes. Death as a result of fulminant hepatic failure is rare, however, older age (over 40 years) and preexisting chronic liver disease increases the risk of severe disease and death from hepatitis A. The person-to-person U.S. multistate outbreaks that began in 2016 have disproportionately affected adults with chronic liver disease and other health problems related to drug use and unstable housing. From 2016 through June 2023, CDC received reports of nearly 45,000 cases of acute HAV infection. Of these, approximately 61% have been hospitalized and nearly 1% (more than 420 people) have died.

Last reviewed: June 25, 2023

If a child is behind on immunizations, the Advisory Committee on Immunization Practices (ACIP) recommends using the minimum intervals between each dose until the child is caught up. The minimum interval for a vaccine can be used as many times as necessary, until the child is back on schedule. See Table 2 of the CDC Recommended Child and Adolescent Immunization Schedule, available at www.cdc.gov/vaccines/schedules/hcp/index.html.

Last reviewed: June 6, 2023

Vaccines must always be dispensed with a prescription or order from a physician or other healthcare provider authorized by the state to prescribe medications. However, there are situations where vaccines can be administered using a standing order or vaccine protocol that is not patient-specific. In these situations, a physician or other healthcare provider does not need to be physically present for the vaccine to be administered. Several studies have shown that the use of standing orders can improve vaccination rates, and ACIP recommends the use of standing orders programs in both outpatient and inpatient settings. A comprehensive set of standing orders for the routine vaccines given to children and adults can be found at www.immunize.org/standing-orders.

Last reviewed: August 22, 2020

Fainting is most commonly reported in adolescents, according to the Vaccine Adverse Event Reporting System. One study showed that 62% of all fainting reports to VAERS were among adolescents 11 to 18 years old; however, due to the limitations of VAERS, we cannot use this system to determine how frequently fainting occurs after vaccination.

Last reviewed: August 31, 2022

The ACIP statement (“Human Rabies Prevention-United States, 2008, Recommendations of the Advisory Committee on Immunization Practices”) was published in MMWR on May 23, 2008. This document updated the status of rabies and anti-rabies biologics in the United States. To view this document, go to www.cdc.gov/mmwr/PDF/rr/rr5703.pdf.

In March 2010, ACIP eliminated the fifth dose of vaccine given post-exposure to previously unvaccinated persons with no immunosuppression. To view these recommendations, go to www.cdc.gov/mmwr/pdf/rr/rr5902.pdf.

In May 2022, ACIP eliminated the third dose of vaccine given in the primary series for pre-exposure prophylaxis and introduced updated risk categories with customized recommendations for long-term follow up after completion of the 2-dose primary series. To view this document, visit www.cdc.gov/mmwr/volumes/71/wr/pdfs/mm7118a2-H.pdf.

Last reviewed: May 14, 2023

It is common practice in many developing countries to administer oral polio vaccine (OPV) to children during both routine visits and periodic vaccination campaigns, so a child’s record may indicate more than 4 doses. Some of these doses may not be valid according to the U.S. immunization schedule.

Doses are considered valid if written documentation indicates that doses of polio vaccine were given after 6 weeks of age and the vaccine received was listed as IPV or trivalent OPV (tOPV). A record simply indicating “OPV” also is acceptable if the OPV was administered before April 1, 2016, and it was not noted as being administered during a vaccination campaign.

There specific criteria for OPV documentation because only trivalent polio vaccine doses count as valid for the U.S. polio vaccination schedule. Trivalent OPV ceased to be used globally in April 2016. OPV administered before April 1, 2016, generally was tOPV. However, “OPV” doses recorded as given during a mass vaccination campaign before April 2016 do not count as valid because such campaigns may have used monovalent or bivalent OPV.

If the history is of a complete series of IPV or tOPV in any combination, at least one dose should be administered on or after 4 years of age and at least 6 months after the previous dose. If a complete series cannot be identified that meets these criteria, then the child should receive as many doses of IPV as needed to complete the U.S. recommended schedule.

Last reviewed: July 23, 2023

All adolescents should receive a dose of MenACWY at 11 or 12 years of age. A second (booster) dose is recommended at 16 years of age. Adolescents who receive their first dose at age 13 through 15 years should receive a booster dose at age 16 years. The minimum interval between MenACWY doses is 8 weeks. Adolescents who receive a first dose after their 16th birthday do not need a booster dose unless they become at increased risk for meningococcal disease. Colleges may not consider a second dose given even a few days before age 16 years as valid, so keep that in mind when scheduling patients. People 19 through 21 years of age are not recommended routinely to receive MenACWY. However, MenACWY may be administered to people age 19 through 21 years as catch-up vaccination for those who have not received a dose after their 16th birthday.

Last reviewed: November 15, 2024

Vaccines should not be stored in vegetable bins nor in the space occupied by vegetable bins of a household-style refrigerator. This area is commonly closer to the motor of the unit and the temperature is different from that in the body of the refrigerator. We recommend that you remove the vegetable bins and put bottles of water in that space to help maintain a constant temperature in your refrigerator. Vaccines should be placed in the center of the refrigerator, away from the walls and floor of the unit in open containers so air can circulate around the vaccines. If using the refrigerator section of a household-style combination refrigerator/freezer unit, you do not want the top storage shelf in the refrigerator to be too close to the vent that comes from the freezer because this can expose your vaccines to freezing temperatures.

Last reviewed: July 26, 2023

Treatment with antibiotics is not a valid reason to defer vaccination. If the child or adult is otherwise well, or has only a minor illness, vaccines should be administered. But if the person has a moderate or severe acute illness (regardless of antibiotic use) vaccination may be deferred until the person’s condition has improved.

Last reviewed: August 29, 2022

ACIP recommendations and package inserts do not always match. Occasionally, ACIP may use different data to formulate its recommendations, or try to add flexibility to its recommendations (as was the case in this situation), which results in a recommendation different than the package insert. Published recommendations of national advisory groups (such as ACIP or AAP’s Committee on Infectious Diseases) should be considered equally as authoritative as those on the package insert. You should consider 8 months 0 days as the maximum age for a dose of rotavirus vaccine.

Last reviewed: June 7, 2023

The ACIP recommends routine administration of a conjugate Hib vaccine series for all infants beginning at age 2 months. Infants 2 through 6 months of age should receive a 3-dose series of ActHIB, Hiberix, Pentacel, or Vaxelis, or a 2-dose series of PedvaxHIB. The first dose can be administered as early as age 6 weeks. Hib-containing vaccine should not be given before 6 weeks of age. Doses given before 12 months of age should be separated by at least 4 weeks. A booster dose (which will be dose 3 or 4 depending on vaccine type used in primary series) of any Hib-containing vaccine is recommended at age 12 through 15 months and at least 8 weeks after the most recent Hib dose. Vaxelis is recommended only for the primary Hib series and is not recommended for use as a booster (4th) dose. A different Hib-containing vaccine licensed for a booster dose should be used.

Medically stable preterm infants should be vaccinated beginning at age 2 months according to the schedule recommended for other infants, on the basis of chronological age. Unimmunized children 60 months and older who have HIV infection should receive 1 dose of Hib vaccine.

Last reviewed: July 31, 2022

In June 2021, ACIP voted to recommend Dengvaxia for routine use in children age 9 through 16 years with laboratory-confirmed previous dengue virus infection and living in areas where CDC has classified dengue as endemic. The recommendation is only for persons with confirmed previous DENV infection because Dengvaxia is associated with an increased risk for severe dengue in those who experience their first natural infection (i.e., primary infection) after vaccination.

The vaccine is not approved for use in U.S. travelers who are visiting but not living in an area where dengue is common.

The most current ACIP recommendations for Dengvaxia are available at www.cdc.gov/mmwr/volumes/70/rr/pdfs/rr7006a1-H.pdf.

CDC has developed a pre-vaccination checklist for evaluating whether a child should receive Dengvaxia: www.cdc.gov/dengue/resources/DVBD_FS_Vaccination_Checklist-508.pdf.

Last reviewed: February 16, 2022

ACIP does not address this issue. However, CDC recommends that these children should each be vaccinated, notwithstanding they are conjoined. We believe even in conjoined twins who share organs and/or blood supply, vaccination of each child would also be indicated. The rationale is one cannot be sure, even in the latter case, that the common organs/blood supply would eliminate vaccine antigens less quickly, or the immune system(s) would respond adequately, to one dose of each vaccine for the two children. Therefore two doses seems appropriate, that is, one dose of each vaccine for each child.

Last reviewed: December 28, 2022

Shingrix was studied in immunocompetent adults in 2 pre-licensure clinical trials. Efficacy against shingles was 97% for people 50–59 years of age, 97% for people 60–69 years of age, and 91% for people 70 years and older. Among people 70 years and older vaccine efficacy was 85% four years after vaccination.

Vaccine effectiveness (VE) has been evaluated for a limited number of specific immunocompromising conditions. VE estimates vary depending upon the underlying cause of immunocompromise. Studies have estimated VE of 68.2% for autologous hematopoietic cell transplant recipients, and 87.2% and 90.5% for patients with hematologic malignancies and potential immune-mediated diseases, respectively.

Last reviewed: March 9, 2022

HBV is stable in the environment and remains viable for 7 or more days on environmental surfaces at room temperature. HBV can be transmitted despite the absence of visible blood. Any high level disinfectant that is tuberculocidal will inactivate HBV. The Environmental Protection Agency also registers disinfectants specifically approved for use against HIV and HBV; a current list is available at this website: www.epa.gov/pesticide-registration/list-d-epas-registered-antimicrobial-products-effective-against-human-hiv-1.

Last reviewed: July 21, 2023

Yes, although the package inserts states that Pediarix should only be given to infants born to mothers who are HBsAg-negative, ACIP voted in 2003 to expand its recommendations for use to include infants born to women whose HBsAg status is positive or unknown beginning no earlier than age 6 weeks.

Last reviewed: July 15, 2023

In April 2018, the Advisory Committee on Immunization Practices (ACIP) published a compilation of all previous recommendations for the prevention of pertussis, tetanus, and diphtheria (MMWR 2018;678 [RR-2]:1-31). The document can be accessed on the CDC website at www.cdc.gov/mmwr/volumes/67/rr/pdfs/rr6702a1-H.pdf.

In January 2020, ACIP published updated Tdap recommendations, stating that either Td or Tdap may be used in situations where Td only was previously recommended. The document can be accessed on the CDC website at www.cdc.gov/mmwr/volumes/69/wr/pdfs/mm6903a5-H.pdf.

Last reviewed: March 31, 2022

Healthcare providers (or other covered entities) may share immunization information with schools or daycare facilities, without authorization, if permitted or required by state law. These state laws would not be preempted by the HIPAA Privacy Rule [45 CFR 160.203(c)].

Last reviewed: June 6, 2023

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