Ask the Experts: All Questions

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Results (1379)

Historically, HAV infection was highly endemic in institutions for people with developmental disabilities as a result of poor hand hygiene, close living conditions and diaper use. As fewer children have been institutionalized and as conditions in institutions have improved, the incidence and prevalence of HAV infection have decreased, although outbreaks can occur in these settings. All children with developmental disabilities should receive HepA vaccine according to U.S. routine vaccine recommendations, including catch up vaccination of all children through age 18 years.

As a strategy to further reduce the risk of hepatitis A outbreaks and reach adults in settings with a high proportion of people with risk factors for HAV infection, the current ACIP recommendations suggest considering HepA vaccination of residents and staff in facilities where hygiene is difficult to maintain, such as group homes for people with developmental disabilities and homeless shelters.

Last reviewed: June 25, 2023

As of 2021, every state has an IIS that is capable of accepting and storing immunization records on individuals of all ages. To find out the status of the IIS in your state you should contact your state IIS program or your state immunization program. CDC maintains a listing of contact information for all state IIS programs at www.cdc.gov/iis/contacts-locate-records/.

Last reviewed: February 16, 2025

MenB vaccines were approved based on the serologic response to the vaccine. Because meningococcal B disease is so rare, no data are available on vaccine effectiveness against clinical disease or duration of protection against clinical disease. Short term protection refers to the known duration of the antibody response. Available data indicate that protective antibody levels wane in most recipients within 1–2 years of completion of the primary series. Antibody levels rise sharply within 1-2 weeks of a booster dose.

Last reviewed: November 15, 2024

With rare exceptions*, all vaccines can be administered at the same visit. There is no upper limit for the number of vaccines that can be administered during one visit. ACIP and AAP consistently recommend that all needed vaccines be administered during an office visit. Vaccination should not be deferred because multiple vaccines are needed. All live vaccines (MMR, varicella, live attenuated influenza, yellow fever, and oral typhoid) can be given at the same visit if indicated. If live vaccines are not administered during the same visit, they should be separated by 4 weeks or more.

When giving several injections at a single visit, separate IM vaccines by at least 1 inch in the body of the muscle if possible to reduce the likelihood of local reactions overlapping. Here are some helpful site maps for different ages so you can record where shots were given:

For infants and toddlers: www.eziz.org/PDF/IMM-718.pdf

For older children: www.aimtoolkit.org/docs/Giving_all_the_doses_12mths.pdf

For adults: eziz.org/assets/docs/ADA/IMM-718A.pdf

For details see ACIP’s “General Best Practices Guidelines for Immunization”, available at https://www.cdc.gov/vaccines/hcp/imz-best-practices/vaccine-administration.html.

*There are 3 exceptions to this general rule: 1) if both pneumococcal conjugate vaccine (PCV13, Prevnar 13, Pfizer) and pneumococcal polysaccharide vaccine (PPSV23, Pneumovax 23, Merck) are indicated for a high-risk patient, these vaccines should not be given at the same visit. The PCV13 should be given first followed by PPSV23 at least 8 weeks later. If PPSV23 has already been given, wait 8 weeks (for a child) or 1 year (for an adult age 19 years or older) before giving PCV13 to avoid interference between the two vaccines. 2) A person with anatomic or functional asplenia or HIV should receive both PCV13 and meningococcal ACWY (MenACWY) vaccines. If Menactra brand (Sanofi) MenACWY is used, the person should first receive all recommended doses of PCV13 followed by Menactra at least 4 weeks later. Menveo (GSK) or MenQuadfi (Sanofi) MenACWY brands can be given at the same time or at any time before or after PCV13. 3) Cholera vaccine should be administered before TY21a vaccine, and 8 hours should separate cholera vaccine and the first dose of TY21a.

Last reviewed: December 28, 2022
Table 2
Tests Results Interpretation Vaccinate?
HBsAg negative susceptible vaccinate if indicated
anti-HBc negative
anti-HBs negative
HBsAg negative immune due to vaccination (or may represent passive transfer of antibodies from receipt of HBIG) no vaccination necessary
anti-HBc negative
anti-HBs positive with >10mIU/mL*
HBsAg negative immune due to natural infection no vaccination necessary
anti-HBc positive
IgM anti-HBc negative
anti-HBs positive
HBsAg negative acute resolving infection no vaccination necessary
anti-HBc positive
IgM anti-HBc positive
anti-HBs positive
HBsAg positive acutely infected no vaccination necessary
anti-HBc positive
IgM anti-HBc positive
anti-HBs negative
HBsAg positive chronically infected no vaccination necessary (may need treatment)
anti-HBc positive
IgM anti-HBc negative
anti-HBs negative
HBsAg negative four interpretations possible† use clinical judgment
anti-HBc positive
anti-HBs negative

* Postvaccination testing, when it is recommended, should be performed 1-2 months after the last dose of vaccine. Infants born to HBsAg-positive mothers should be tested for HBsAg and anti-HBs after completion of at least 3 doses of a licensed hepatitis B vaccination series, at age 9-18 months (generally at the next well child visit).

†1. May be distantly immune, but the test may not be sensitive enough to detect a very low level of anti-HBs in serum

2. May be susceptible with a false positive anti-HBc

3. May be chronically infected and have an undetectable level of HBsAg present in the serum

4. Passive transfer of antibody following HBIG administration or from an HBsAg-positive mother to her newborn

Last reviewed: January 17, 2025

Healthcare providers should refer to the catch-up schedule published as part of the CDC Recommended Child and Adolescent Immunization Schedule (available at www.cdc.gov/vaccines/hcp/imz-schedules/child-adolescent-catch-up.html). The catch-up schedule will help determine the number of additional doses needed and the minimum intervals between doses. However, if a healthy child receives a single dose of Hib vaccine at age 15 months or older, he or she does not need any further doses regardless of the number of doses received before age 15 months. Some high-risk children between the age of 15 months and 59 months will be recommended for two doses of Hib vaccine based on previous history of incomplete vaccination; these special situations are reviewed in the Hib notes section of the schedule: www.cdc.gov/vaccines/hcp/imz-schedules/child-adolescent-notes.html.

Last reviewed: January 21, 2025

Children with confirmation of previous DENV infection need three doses of Dengvaxia, given 6 months apart, for complete protection (0, 6 months, 12 months). Recipients achieve significant protection following dose 1.

Last reviewed: January 17, 2025

The following information is taken from the CDC web page with information on the vaccination of U.S.-bound refugees and V-93 applicants (www.cdc.gov/immigrant-refugee-health/hcp/panel-physicians/vaccination.html):

CDC has specific criteria to determine which vaccines applicants for a United States Immigrant Visa are required to show proof of having received.

The criteria are as follows:

The vaccine must be an age-appropriate vaccine, as recommended by the Advisory Committee on Immunization Practices (ACIP) for the general U.S. population AND at least one of the following:

  • The vaccine must protect against a disease that has the potential to cause an outbreak. An outbreak is defined as the occurrence of more cases of disease than expected in a given area or among a specific group of people, over a given period of time. For endemic diseases, an outbreak occurs when incidence rises above the normally expected level. For diseases with seasonal variation, the average incidence rates over particular weeks or months of previous years, or average high or low levels over a period of years, may be used as baselines.
  • The vaccine must protect against a disease that has been eliminated in the United States or is in the process of being eliminated in the United States.

Therefore, the vaccines required for applicants do not include all the vaccines recommended by the ACIP and CDC for routine U.S. domestic use, and are limited to vaccination for the following diseases:

  • Diphtheria
  • Tetanus
  • Pertussis
  • Polio
  • Measles
  • Mumps
  • Rubella
  • Rotavirus
  • Haemophilus influenzae type b (Hib)
  • Hepatitis A
  • Hepatitis B
  • Meningococcal disease
  • Varicella
  • Pneumococcal disease
  • Influenza
  • COVID-19

ACIP recommends vaccines for a certain age range in the general U.S. public. ACIP recommendations are used to decide which vaccines are age-appropriate for the general immigrant population. Refer to the CDC table of vaccines required for immigrant visa applicants by age: www.cdc.gov/immigrant-refugee-health/media/pdfs/Vaccine-Requirements-According-to-Applicant-Age-panel-physicians-p.pdf.

Children adopted from outside the U.S. and political refugees are recommended to receive age-appropriate vaccination, with catch-up vaccination as appropriate. More information is available in the “Special Situations” section of CDC’s General Best Practices for Immunization, available at  www.cdc.gov/vaccines/hcp/imz-best-practices/special-situations.html#cdc_report_pub_study_section_7-persons-vaccinated-outside-the-united-states. People entering the U.S. as visitors are not required to provide proof of vaccination regardless of the length of stay.

Last reviewed: January 20, 2025


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Last reviewed: May 23, 2023


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Last reviewed: October 25, 2024


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Last reviewed: December 6, 2024

ACIP supports vaccination of preterm infants according to the same schedule and precautions as full-term infants and under the following conditions: if the infant’s chronological age meets the age requirements for rotavirus vaccine (for example, age 6 weeks to 14 weeks 6 days for dose #1), the infant is clinically stable, and the vaccine is administered at the time of discharge from the hospital or after discharge from the hospital.

Last reviewed: June 7, 2023

No, it is not. It is only recommended for children and teens ages 9 through 16 who reside in dengue endemic areas.

Last reviewed: January 17, 2025

Clinicians and patients should make every effort to ensure that two doses of Shingrix are administered within the recommended interval of 2 to 6 months. If more than 6 months have elapsed since the first dose of Shingrix, administer the second dose when possible. Do not restart the vaccine series.

Additional information for clinicians about Shingrix is available on the CDC website at www.cdc.gov/vaccines/vpd/shingles/hcp/index.html.

Last reviewed: March 9, 2022

Serologic testing for immunity is not necessary or recommended after routine vaccination of infants, children, or adults. Testing for anti-HBs after vaccination is recommended for the following groups whose subsequent clinical management depends on knowledge of their immune status:

  • Infants born to HBsAg-positive women and infants born to women whose HBsAg status remains unknown (for example, infants surrendered shortly after birth); postvaccination serologic testing should consist of testing for anti-HBs and HBsAg and should not occur before age 9 months
  • Healthcare professionals and public safety workers at risk for blood or body fluid exposure
  • Hemodialysis patients (and other persons who might require outpatient hemodialysis), people living with HIV, and other immunocompromised people (such as hematopoietic stem-cell transplant [HSCT] recipients or people receiving chemotherapy), to determine the need for revaccination and the type of follow-up testing, and
  • Sex partners of HBsAg-positive people, to determine if they have not achieved immunity and will need revaccination and to continue to use other methods of protection against HBV infection.

Testing of individuals other than infants should be performed 1–2 months after administration of the final dose of the vaccine series using a method that allows determination of a protective concentration of anti-HBs (10 mIU/mL or higher). Testing of infants should take place after administration of the final dose of the vaccine series when the infant is age 9 through 12 months. Testing should not be done earlier than 9 months to avoid inadvertent detection of HBIG administered at birth and to maximize the likelihood of detecting HBV infection, if present.

Last reviewed: January 17, 2025

MMR can be given to children as young as 6 months of age who are at high risk of exposure such as during international travel or a community outbreak. However, doses given BEFORE 12 months of age cannot be counted toward the 2-dose series for MMR.

Last reviewed: June 19, 2023

No. Pediarix is intended to be used only for doses 1, 2, or 3 of the DTaP primary series; consequently, using Pediarix for DTaP #4 is off-label and not recommended. You should take measures to prevent this error in the future. The DTaP, IPV, and HepB doses given in this scenario do not need to be repeated as long as you met the recommended minimum intervals for each vaccine component (DTaP, IPV, HepB). If you did meet the minimum intervals, the doses should be counted as valid.

Last reviewed: January 27, 2025

The following vaccines are recommended for new mothers before they leave the hospital: (1) mothers without documentation of previous Tdap vaccination need a dose to protect themselves; (2) mothers who did not receive influenza vaccination during pregnancy need to be vaccinated if it is still influenza vaccination season (October through March); (3) mothers who tested susceptible to rubella on prenatal testing need MMR vaccine even if they have 1 or 2 documented doses of MMR in their medical record; (4) mothers who are not immune to chickenpox need 2 doses of varicella vaccine – the first dose before hospital discharge and the second dose 4 to 8 weeks after the first dose.

Last reviewed: August 29, 2022

Vaccine efficacy is 80%–85% following 3 doses of DTaP vaccine. Efficacy data following just 1 or 2 doses are lacking but are likely lower. The most effective way to prevent pertussis in early infancy is to vaccinate the mother between 27 and 36 weeks’ gestation. Antipertussis antibodies generated by the mother’s immune system are passed across the placenta to the fetus. One dose of Tdap should be administered during each pregnancy, preferably between 27 and 36 weeks’ gestation. Available data suggest that vaccinating closer to 27 weeks will maximize passive antibody transfer to the infant. A CDC evaluation found Tdap vaccination during the third trimester of pregnancy prevents 78% of pertussis cases in infants younger than 2 months of age and that maternal vaccination reduces the risk of infant hospitalization for pertussis by 90% (www.cdc.gov/pertussis/hcp/vaccine-recommendations/vaccinating-pregnant-patients.html).

Last reviewed: March 31, 2022

No. If a healthy child receives a dose of Hib vaccine at 15 months of age or older, he or she does not need any further doses regardless of the number of doses received before 15 months of age.

Last reviewed: January 21, 2025

CDC’s Vaccine Storage and Handling Toolkit states that if other medications and biological products must be stored in the same unit as vaccines, they must be clearly marked and stored in separate containers or bins from vaccines. Potentially contaminated items (e.g., blood, urine) should be properly contained and stored below vaccines due to risk of contamination from drips or leaks. The freezer of a household-grade unit may be used for non-vaccine, medical storage, so long as the use does not compromise the temperature range within the refrigerator compartment where vaccine is stored.

Last reviewed: July 26, 2023

No. In June 2019, the Advisory Committee on Immunization Practices (ACIP) voted to recommend routine catch-up HPV vaccination of all previously unvaccinated or incompletely vaccinated males age 22 through 26, matching the recommendation for females. HPV vaccination recommendations now differ by age group only, not by biological sex. There is a routine recommendation for vaccination of all people 9 through 26 years of age and a shared clinical decision-making recommendation based on risk and preference for people 27 through 45 years of age.

Current ACIP recommendations for HPV vaccine are listed at www.cdc.gov/acip-recs/hcp/vaccine-specific/hpv.html.

Last reviewed: March 2, 2024

Under section 564 of the Federal Food, Drug, and Cosmetic Act (FD&C Act), the FDA Commissioner may allow unapproved medical products or unapproved uses of approved medical products to be used in an emergency to diagnose, treat, or prevent serious or life-threatening diseases or conditions caused by chemical, biological, radiological or nuclear threat agents when there are no adequate, approved, and available alternatives. Vaccines that receive an EUA may later be fully licensed by the FDA.

Last reviewed: November 16, 2024

Several small outbreaks of meningococcal serogroup B disease have occurred on college campuses since 2013. However, the disease incidence in college students remains very low (0.03 cases per 100,000 college students age 18 to 24 years in 2020). ACIP does not routinely recommend MenB vaccine for college students. However, the recommendation for shared clinical decision-making applies to all college students age 16 through 23 years who may choose to receive MenB vaccine to reduce their risk of meningococcal serogroup B disease. In addition, some colleges and universities require MenB vaccination for incoming students.

If a college student completes the MenB vaccine series at least 6 months to 1 year before being identified as at risk during an outbreak, a single booster dose of the same brand can boost levels of protective antibodies within 1-2 weeks. The ability to be protected quickly during an outbreak by a single booster dose may be an important consideration for college students, families, and administrators when deciding about getting the MenB vaccine primary series.

Last reviewed: November 15, 2024

Yes. One dose of MenACWY vaccine is recommended for all first-year college students who are or will be living in a residence hall if they are previously unvaccinated, have not received a dose of MenACWY since turning 16, or if their most recent dose (given after turning 16) was not given within the past 5 years.

Last reviewed: November 15, 2024

The Advisory Committee on Immunization Practices (ACIP) does not address this issue. There is no recommended order in which the vaccines should be given. A best practice strategy to decrease injection or procedural pain is to administer the vaccine that causes the most pain (stinging, for example) last. For more information on vaccine administration, please see the “Vaccine Administration” chapter of Epidemiology and Prevention of Vaccine-Preventable Diseases at www.cdc.gov/pinkbook/hcp/table-of-contents/chapter-6-vaccine-administration.html.

Last reviewed: December 28, 2022

Only the RSVpreF vaccine, Abrysvo by Pfizer, is licensed and recommended for one-time use between 32 weeks and 36 weeks 6 days of gestation to prevent RSV-associated lower respiratory tract disease in infants younger than 6 months old. Do not use Arexvy (GSK) or mResvia (Moderna) during pregnancy. If a pregnant person received an RSV vaccine before the current pregnancy, do not use Abrysvo during this pregnancy. Instead, counsel them that a dose of nirsevimab (Beyfortus, Sanofi) will be needed to protect the infant from RSV after birth.

Last reviewed: August 25, 2024

The “same day” generally means at the same visit. This interval has not been precisely defined and probably will never be since it would be extremely difficult to study in order to develop an evidence-based recommendation. Immunization programs (and their computer systems) likely define this differently. It seems reasonable that if two vaccines were given on the same date then they would both be valid.

Last reviewed: June 6, 2023

No. In general, although it is not ideal, receiving extra doses of vaccine poses no medical problem. Receiving excessive doses of tetanus toxoid (e.g., DTaP, DT, Tdap, or Td) can increase the risk of a local adverse reaction, however. For details, see Extra Doses of Vaccine Antigens in the ACIP’s “Best Practice Guidelines for Immunization” at www.cdc.gov/vaccines/hcp/imz-best-practices/timing-spacing-immunobiologics.html.

Vaccination providers frequently encounter people who do not have adequate documentation of vaccinations. Providers should only accept written, dated records as evidence of vaccination. With the exception of influenza vaccine and pneumococcal polysaccharide vaccine, self-reported doses of vaccine without written documentation should not be accepted. An attempt to locate missing records should be made whenever possible by contacting previous healthcare providers, reviewing state or local immunization information systems, and searching for a personally held record.

If records cannot be located or will definitely not be available anywhere because of the patient’s circumstances, children without adequate documentation should be considered susceptible and should receive age-appropriate vaccination. Serologic testing for immunity is an alternative to vaccination for certain antigens (e.g., measles, rubella, hepatitis A, diphtheria, and tetanus).

Last reviewed: August 31, 2022

Every attempt should be made to adhere to the recommended vaccination schedules. Once vaccination is initiated, delays of a few days for individual doses are unimportant, but the effect of longer lapses of weeks or more is unknown. Most interruptions in the vaccine schedule do not require reinitiation of the entire series. For most minor deviations from the schedule, vaccination can be resumed as though the patient were on schedule. For example, if a patient misses the dose scheduled for day 7 and presents for vaccination on day 10, the day 7 dose should be administered that day and the schedule resumed, maintaining the same interval between doses. In this scenario, the remaining doses would be administered on days 17 and 31. When substantial deviations from the schedule occur, immune status should be assessed by performing serologic testing 7–14 days after administration of the final dose in the series. Postexposure prophylaxis with rabies vaccine is described in detail at www.cdc.gov/mmwr/pdf/rr/rr5902.pdf.

Last reviewed: May 14, 2023

Polio vaccine given outside the United States is valid if written documentation indicates that all doses were given after 6 weeks of age and the vaccine received was IPV or trivalent OPV (tOPV). Only trivalent polio vaccine counts toward the U.S. schedule. No doses of OPV given since April 1, 2016, count toward the U.S. polio vaccination schedule because, on that date, all countries routinely using tOPV switched to bivalent OPV. Please see other detailed answers concerning details on assessment of OPV doses by the date of administration.

If both tOPV and IPV were or will be administered as part of a series, the total number of doses needed to complete the series is the same as that recommended for the U.S. IPV schedule. If the child is younger than 4 years of age a total of 4 doses of polio vaccine are recommended. If the child is currently 4 years of age or older, a total of 3 doses completes the series. A minimum interval of 4 weeks should separate doses in the series, with the final dose administered on or after the fourth birthday and at least 6 months after the previous dose. If only tOPV was administered, and all doses were given before 4 years of age, 1 dose of IPV should be given at 4 years of age or older, at least 6 months after the last tOPV dose.

Last reviewed: July 23, 2023

No. A healthcare provider’s diagnosis or verification of a history of shingles is acceptable evidence of immunity to varicella. According to ACIP, acceptable evidence of varicella immunity in healthcare personnel includes (1) documentation of 2 doses of varicella vaccine given at least 28 days apart, (2) history of varicella or herpes zoster based on clinician diagnosis, (3) laboratory evidence of immunity, or (4) laboratory confirmation of disease.

Last reviewed: May 16, 2023

No. People with chronic liver disease are not at increased risk for acquiring HAV infection. However, they are at an increased risk for life-threatening, fulminant (severe and sudden) hepatitis if they become infected with hepatitis A. People considered to have chronic liver disease include those with hepatitis B or C infection, cirrhosis, fatty liver disease, alcoholic liver disease, and autoimmune hepatitis.

Last reviewed: June 25, 2023

The recommendations for pneumococcal vaccination of children and adults vary depending upon the specific vaccines available, and the recipient’s age, pneumococcal vaccination history, and medical or behavioral risk factors. CDC has summarized all of its recommendations at this site: www.cdc.gov/pneumococcal/hcp/vaccine-recommendations/index.html.

CDC has created an app for pneumococcal vaccine evaluation of individual patients. For more information, or to learn how to download the PneumoRecs VaxAdvisor mobile app, visit www.cdc.gov/pneumococcal/hcp/vaccine-recommendations/app.html.

Recommendations are summarized by Immunize.org in the following resources:

Last reviewed: November 13, 2024

Patient-held cards are an important part of a person’s medical history. The person may move to another state or need medical care at a facility within or outside the state without access to the IIS in which their records are documented, and the personal record may be the only vaccination record available.

Last reviewed: February 16, 2025

ACIP recommends that people working in healthcare settings be vaccinated against COVID-19, influenza, hepatitis B, measles, mumps, rubella, varicella, and pertussis. Adults are generally assumed to have been vaccinated against polio in childhood; any adult known or strongly suspected of being unvaccinated against polio should be vaccinated. For measles, mumps, rubella, and varicella, serologic evidence of immunity is an acceptable substitute for documentation of vaccination. In addition, microbiologists working in a laboratory should receive vaccination against meningococcal ACWY and meningococcal serogroup B disease. In rare cases, some laboratory personnel should also receive a single polio vaccine booster and typhoid vaccines. For more information, refer to the current CDC recommended adult immunization schedule or the 2011 ACIP recommendations for immunization of healthcare personnel, www.cdc.gov/mmwr/pdf/rr/rr6007.pdf.

Last reviewed: January 27, 2025


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Last reviewed: May 9, 2023


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Last reviewed: May 23, 2023


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Last reviewed: December 6, 2024

CDC recommends the use of bins, baskets, or some other type of uncovered containers that allow for organization and air circulation for vaccines and diluents within the storage unit. Storage in boxes or bins can help maintain temperature longer, especially if power is lost. Perforated bins may allow for better air circulation around the vaccine, thus helping to maintain correct temperature.

CDC does not have a specific recommendation for brands of containers or bins for storage of vaccine. We recommend that you contact your state immunization program, as they may have suggestions for purchasing this equipment. If you are a Vaccines for Children (VFC) program provider, you should contact your immunization program to ensure that you are in compliance with VFC policy.

Last reviewed: July 26, 2023

ACIP recommends vaccination of preterm infants according to the same schedule and precautions as full-term infants. In preterm infants (as in full-term infants), the maximum chronological age for the first dose is 14 weeks 6 days. Vaccination should not be initiated for infants aged 15 weeks 0 days or older because of insufficient data on safety of dose 1 of rotavirus vaccine in older infants. For more information, see page 19 of ACIP’s recommendations on rotavirus vaccination, available at www.cdc.gov/mmwr/PDF/rr/rr5802.pdf.

Last reviewed: June 7, 2023

With the exception of two vaccines used to prevent smallpox or mpox (previously known as monkeypox), there is no recommendation to wait until a vaccine reaches room temperature before administration. The vaccine should be administered as soon as it is prepared.

The live smallpox (vaccinia) vaccine, ACAM2000 (Emergent Product Development Gaithersburg, Inc.) and the non-replicating, live smallpox and mpox vaccine, Jynneos (Bavarian Nordic) should be brought to room temperature before use, according to the package inserts for these two products.

Last reviewed: December 28, 2022

People born before 1957 lived through several years of epidemic measles before the first measles vaccine was licensed in 1963. As a result, these people are very likely to have had measles disease. Surveys suggest that 95% to 98% of those born before 1957 are immune to measles. Persons born before 1957 can be presumed to be immune. However, if serologic testing indicates that the person is not immune, at least 1 dose of MMR should be administered.

Last reviewed: June 19, 2023

Yes. ACIP recommends that people who previously received Zostavax receive 2 doses of Shingrix. The first dose of Shingrix may be given a minimum of 8 weeks after Zostavax.

Last reviewed: March 9, 2022

FDA licensed Pentacel in 2008 as a 4-dose series in infants and children at ages 2, 4, 6, and 15–18 months. It should not be used for any dose in the primary series for children age 5 years or older or as the booster dose for children ages 4 through 6 years. The DTaP-IPV component is supplied as a sterile liquid, which is used to reconstitute lyophilized (freeze-dried) ActHIB vaccine. The two components of the vaccine should be stored together in the carton to reduce the chance of giving one component of the vaccine without the other. The DTaP-IPV component should never be administered alone.

Last reviewed: January 27, 2025

Yes. The January 2020 ACIP updated statement on the use of Tdap (available at www.cdc.gov/mmwr/volumes/69/wr/pdfs/mm6903a5-H.pdf) states that a child who receives a dose of Tdap from age 7–9 years as part of the catch-up series (as in this case), should receive another dose of Tdap at age 11 or 12 years.

Last reviewed: March 31, 2022

The National Childhood Vaccine Injury Act (NCVIA), enacted in 1986, set forth 3 basic requirements for all vaccination providers, which are:

  • Providers must give the patient (or parent/legal representative of a minor) a copy of the relevant federal “Vaccine Information Statement” (VIS) for the vaccine they are about to receive.
  • Providers must record certain information about the vaccine(s) administered in the patient’s medical record or a permanent office log.
  • Providers must document any adverse event following the vaccination that the patient experiences and that becomes known to the provider, whether or not it is felt to be caused by the vaccine, and submit the report to the Vaccine Adverse Event Reporting System (VAERS) at https://vaers.hhs.gov.
Last reviewed: February 16, 2025

Catch-up HPV vaccination is not recommended for adults older than 26 years of age. Instead, shared clinical decision-making regarding HPV vaccination is recommended for some adults aged 27 through 45 years who are not adequately vaccinated and want to be protected from ongoing risk of acquiring new HPV infection.

Ideally, HPV vaccine should be administered before potential exposure to HPV through sexual contact.

Last reviewed: March 2, 2024

Some isolated positive anti-HBc results are false positives (it is the most common false positive HBV marker). If that can be established, the individual can and likely should be vaccinated, assuming there is an indication or desire to be protected. If the positive anti-HBc is believed to be a true positive, the individual would not require vaccination since they have already (presumably) had HBV infection. Isolated positive anti-HBc could indicate low-level chronic infection. In an infant isolated anti-HBc could indicate passive transfer of antibody from a mother who is HBsAg positive, which is why anti-HBc testing of infants is not recommended.

Additional resources for the evaluation of isolated anti-HBc antibody results are available from the University of Washington: www.hepatitisb.uw.edu/go/screening-diagnosis/diagnosis-hbv/core-concept/all and from CDC: www.cdc.gov/hepatitis-b/hcp/diagnosis-testing/#cdc_hcp_diagnosis_interpreting-how-to-interpret-test-results.

Last reviewed: January 17, 2025

ACIP does not identify incarceration as an indication for meningococcal ACWY vaccination. Providers are always free to use their clinical judgment in situations not addressed by ACIP.

Last reviewed: November 15, 2024

S. pneumoniae bacteria are serotyped based on the polysaccharides in the outer capsule of the bacteria. Serotypes vary in how common they are and in what percentage of pneumococcal disease they cause.

Among the PCV vaccines, PCV13 includes serotypes: 1, 3, 4, 5, 6A, 6B, 7F, 9V, 14, 18C, 19A, 19F and 23F. PCV15 includes all PCV13 serotypes plus 22F and 33F. PCV20 includes all PCV15 serotypes plus 8, 10A, 11A, 12F, and 15B. PPSV23 vaccine does not contain serotype 6A, but contains 19 other serotypes present in PCV20, plus serotypes 2, 9N, 17F, and 20.

PCV21 is designed to target additional serotypes causing a significant proportion of disease in adults that are not prevented by the vaccines approved for children. It does not contain 10 serotypes found in other pneumococcal vaccines approved for children (1, 4, 5, 6B, 9V, 14, 18C, 19F, 23F, 15B, or 2). Instead, it contains an additional 11 serotypes not found in PCV20: 9N, 17F, 20, 15A, 15C, 16F, 23A, 23B, 24F, 31, and 35B. Because of these differences, CDC estimates that PCV20 targets serotypes that cause between 54% and 65% of invasive pneumococcal disease (IPD) in adults, and PCV21 targets serotypes that cause between 77% and 85% of IPD in adults.

PCV13 PCV15 PCV20 PPSV23 PCV21
1 x x x x
3 x x x x x
4 x x x x
5 x x x x
6A x x x x
6B x x x x
7F x x x x x
9V x x x x
14 x x x x
18C x x x x
19A x x x x x
19F x x x x
23F x x x x
22F x x x x
33F x x x x
8 x x x
10A x x x
11A x x x
12F x x x
15B x x
2 x
9N x x
17F x x
20 x x
15A x
15C x
16F x
23A x
23B x
24F x
31 x
35B x
Last reviewed: November 13, 2024

All nine 2024-25 influenza vaccines approved for adults are trivalent, containing two influenza A strains and one influenza B strain.

There are five injectable inactivated influenza vaccine (IIV) options approved for use in all adults age 18 years or older. Four egg-based standard dose IIV vaccines (SD-IIVs) and one cell culture-based one (ccIIV) are available, all given as an intramuscular (IM) injection:

  • Afluria (CSL Seqirus): 0.5 mL/dose
  • Fluarix (GSK): 0.5 mL/dose
  • FluLaval (GSK): 0.5 mL/dose
  • Fluzone (Sanofi): 0.5 mL/dose
  • Flucelvax (ccIIV, CSL Seqirus) cell culture-based (no egg antigen): 0.5 mL/dose

One egg-based live attenuated nasal spray vaccine, FluMist (LAIV, AstraZeneca), is an option for healthy, non-pregnant adults through age 49 years: 0.2 mL (given intranasally, 0.1 mL in each nostril).

Three injectable vaccines, all given IM, are ACIP-preferred options for adults age 65 years or older:

  • Recombinant influenza vaccine, Flublok (RIV, Sanofi): 0.5 mL/dose, licensed for use in adults age 18 or older
  • Fluzone High-Dose (egg-based HD-IIV, Sanofi): 0.5 mL/dose, licensed for adults age 65 years and older
  • Fluad (egg-based aIIV with MF59 adjuvant, CSL Seqirus): 0.5 mL/dose, licensed for adults age 65 years and older

Although licensed by FDA for use in adults age 65 years or older, ACIP also recommends off-label use of Fluzone HD or Fluad as acceptable options for influenza vaccination of solid organ transplant recipients age 18 through 64 years who are on immunosuppressive medication regimens, without a preference over other age-appropriate IIVs or RIV.

Last reviewed: August 11, 2024

For intervals of 3 months or less, you should use 28 days (4 weeks) as a “month.” For intervals of 4 months or longer, you should consider a month a “calendar month”: the interval from one calendar date to the next a month later. This is a convention that was introduced on the childhood schedule in 2002 and discussed in the paper “Evaluation of Invalid Vaccine Doses” (Stokley S, Maurice E, Smith PJ, et al. American Journal of Preventive Medicine, 2004; 26[1]: 34–40).

Last reviewed: June 6, 2023

As the name implies, VAERS is a nationwide system for monitoring adverse events following vaccination. VAERS is operated jointly by the FDA and the CDC since 1990.

Last reviewed: August 31, 2022

People who receive a mixed series of OPV and IPV should receive a total of either 3 or 4 doses depending on the age at the time of the last dose. In this case the recent dose of IPV can be counted as the third and final dose in the series. The minimum interval between the next-to-last and last doses in the polio vaccination series is 6 months and the last dose should be at age 4 years or older.

Last reviewed: July 23, 2023

Recombinant zoster vaccine (RZV, Shingrix, GSK) does not count as the first of two doses of varicella vaccine. Shingrix is not licensed and has not been evaluated for the prevention of primary varicella infection. To meet the immigration requirements, you should give a dose of varicella vaccine now and a second dose at least 4 weeks later. The varicella vaccine doses will not be harmful and will allow your patient to meet the regulatory requirement.

Last reviewed: May 16, 2023

Yes. A pregnant person should receive rabies vaccine if indicated. No fetal abnormalities have been reported with the rabies vaccine. A pregnant person can receive routine pre-exposure vaccination against rabies if the risk of exposure is high.

Last reviewed: August 30, 2020

Hepatitis A cannot be differentiated from other types of viral hepatitis on the basis of clinical or epidemiological features alone. Appropriate blood tests must be used.

  • Anti-HAV: Total antibody to HAV. This diagnostic test detects total antibody of both IgG and IgM subclasses of HAV. If positive, it indicates either acute or resolved infection.
  • IgG anti-HAV: IgG antibody is a subclass of anti-HAV. It appears early in the course of infection, remains detectable for the person’s lifetime and provides lifelong protection against disease. Its presence indicates immunity through either HAV infection or HepA vaccination.
  • IgM anti-HAV: IgM antibody is a subclass of anti-HAV. Its presence indicates a recent infection with HAV (6 months or less). It is used to diagnose acute (recently acquired) hepatitis A. Because of the risk of false positive IgM anti-HAV results, people should only be tested for IgM anti-HAV if they are symptomatic and suspected of having acute hepatitis A illness.
  • HAV RNA tests also may be used to diagnose acute infection through the direct detection of viral RNA in serum or stool.

Total anti-HAV, which appears early in the course of infection, remains detectable for the person’s lifetime and indicates lifelong protection against the infection/disease. To confirm a diagnosis of acute HAV infection, serologic testing for IgM anti-HAV is required. In the majority of persons, serum IgM anti-HAV becomes detectable 5 to 10 days before onset of symptoms and lasts about 6 months. However, there have been reports of persons who test positive for IgM anti-HAV for up to a year or more following infection. An educational program on the interpretation of hepatitis A serology is available on the CDC website at www.cdc.gov/hepatitis/hcp/training/.

Last reviewed: June 25, 2023

Both MenB vaccine products, Trumenba (MenB-Fhbp, Pfizer) and Bexsero (MenB-4C, GSK) are routinely given as a 2-dose series with doses administered at least 6 months apart. A 3-dose schedule is recommended for people who need rapid protection against MenB due to an increased risk of MenB disease. For the 3-dose schedule, dose 2 is given 1-2 months after dose 1 and dose 3 at least 6 months after dose 1.

Penbraya (MenABCWY, Pfizer) contains MenB-Fhbp (Trumenba) and is given as two doses, 6 months apart, when vaccination against all 5 serogroups is needed. For adolescents and adults not at increased risk (who need only one dose of MenACWY vaccine), if Penbraya is used, Trumenba should be administered to complete the 2-dose MenB series. For people age 10 years or older at increased risk of meningococcal disease, Penbraya may be used for additional MenACWY and MenB doses (including booster doses) when both vaccines would be given on the same clinic day and at least 6 months have elapsed since most recent Penbraya dose.

In August 2024, FDA revised the licensed schedule for Bexsero to be the same as the schedule and dosing intervals of the other MenB vaccine product, Trumenba. The change was made due to evidence of a small, but significant, improvement in the immune response to Bexsero when 2 doses were given 6 months apart, instead of 1 month apart, as previously licensed. As with Trumenba, a third dose of Bexsero is due, at least 4 months after the second dose and 6 months after the first, if dose 2 is given less than 6 months after dose 1. No additional doses are recommended for people who previously completed the 2-dose Bexsero series using a 1-month interval as licensed and recommended at the time.

Last reviewed: November 15, 2024

Yes. Receipt of RhoGam is not a reason to delay vaccination. See the ACIP “General Best Practices Guidelines for Immunization” at www.cdc.gov/vaccines/hcp/imz-best-practices/timing-spacing-immunobiologics.html.

Last reviewed: August 29, 2022

If the child received a primary series (2 or 3 doses, depending upon the product) of Hib vaccine in the first year of life, then the final (booster) dose of the series may be given as early as 12 months, provided at least 2 months have passed since the last dose. An unvaccinated 12–14-month-old child should receive one dose as a primary series, and a booster dose 2 months later. Unvaccinated healthy children 15–59 months of age need only a single dose of any licensed conjugate Hib vaccine. Some high-risk children 15–59 months of age are recommended for two doses of Hib vaccine based on previous history of incomplete vaccination; these special situations are reviewed in the Hib notes section of the schedule: www.cdc.gov/vaccines/hcp/imz-schedules/child-adolescent-notes.html.

Last reviewed: January 21, 2025

No. Dengvaxia is FDA-licensed only for children and teens ages 6 years through 16 years.

Last reviewed: January 17, 2025

You can get this information from CDC’s Travel Health website at wwwnc.cdc.gov/travel/. CDC also publishes Health Information for International Travel (a.k.a. the “Yellow Book”) as a reference for those who advise international travelers of health risks. The Yellow Book is written primarily for healthcare providers, although others might find it useful. The contents of the book are available on the CDC Travel Health website. The book can also be ordered in print form. See the Yellow Book at wwwnc.cdc.gov/travel/page/yellowbook-home.

For Immunize.org’s curated list of resources for travel vaccination, see www.immunize.org/vaccines/travel-vaccines/.

Last reviewed: January 20, 2025

In August 2024, FDA revised the licensed schedule for Bexsero to be the same as the schedule and dosing intervals of the other MenB vaccine product, Trumenba (Pfizer). The change was made due to evidence of a small, but significant, improvement in the immune response to Bexsero when 2 doses were given 6 months apart, instead of 1 month apart, as previously licensed. No additional doses are recommended for people who completed the 2-dose Bexsero series using a 1-month interval, as licensed and recommended at the time.

A 3-dose schedule of Bexsero (dose 2 given 1-2 months after dose 1, and dose 3 given at least 6 months after dose 1 and 4 months after dose 2) is recommended for people who require accelerated protection from meningococcal B disease (those at increased risk).

Under the current Bexsero and Trumenba schedules, any MenB vaccine recipient whose second dose is administered less than 6 months after dose 1 should receive a third dose at least 6 months after dose 1 and 4 months after dose 2.

Last reviewed: November 15, 2024

Dose 3 of a 3-dose MenB series should be administered at least 6 months after dose 1 and 4 months after dose 2. In this case, an additional (fourth) dose may be administered at least 4 months after the invalid, early dose 3 and 6 months after dose 1. Review the dosing error and the correct schedule with staff and take other appropriate measures to prevent this error from occurring in the future.

Last reviewed: November 15, 2024

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