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 (1379)

A refrigerator or freezer that is NSF-certified for vaccine storage means the units have been tested and certified to meet the NSF/American National Standards Institute (ANSI) 456 standard. The NSF/ANSI 456 standard (or simply “NSF 456” standard) defines the criteria for construction and performance of vaccine refrigerators and freezers used in healthcare settings where vaccines are given. These criteria were developed through a collaboration with NSF, CDC, healthcare providers, public health agencies, equipment manufacturers, and vaccine manufacturers, including experts from Immunize.org.

The NSF 456 certification is a voluntary standard. CDC does not require NSF-certified units for vaccine storage in the Vaccines for Children program or any other federal program. Not all storage units capable of reliably storing vaccines have this certification; however, all storage unit models with this certification have been designed and proven to properly store vaccines under a range of normal clinic conditions. NSF-certified units would be good options for clinic staff to consider when purchasing vaccine storage units.

Last reviewed: July 26, 2023

If the product used for a previous dose is unknown, and the infant is at an age when the vaccine can still be given, give a total of 3 doses of rotavirus vaccine. All doses should be administered by age 8 months and 0 days.

Last reviewed: June 7, 2023

Yes. All children less than 5 years old need at least one dose of Hib vaccine on or after the first birthday. The last dose should be separated from the previous dose by at least 8 weeks.

Last reviewed: January 21, 2025

Here are the suggested volumes:

Deltoid:

  • Average 0.5 mL
  • Range 0.5–2 mL

Vastus Lateralis:

  • Average 1–4 mL
  • Range 1–5 mL

Infants and toddlers would fall at the lower end of the range, whereas adolescents and adults would generally fall on the higher end of the range.

Last reviewed: December 28, 2022

The recommended interval between Shingrix doses is 2 to 6 months. The minimum interval between doses of Shingrix is 4 weeks. If the second RZV dose is given more than 4 days sooner than 4 weeks after the first dose, a valid second dose should be repeated at least 4 weeks after the dose given too early.

For adults who are or will be immunodeficient or immunosuppressed and who would benefit from a shorter vaccination schedule, the second dose can be administered 1–2 months (a minimum of 4 weeks) after the first dose.

Last reviewed: March 9, 2022

Approximately 7% of people do not develop measles immunity after the first dose of vaccine. This occurs for a variety of reasons. The second dose is to provide another chance to develop measles immunity for people who did not respond to the first dose. About 97% of people develop immunity to measles after two doses of measles-containing vaccine.

Last reviewed: June 19, 2023

Yes, as long as minimum intervals between doses are maintained.

Last reviewed: January 27, 2025

Due to theoretical risk to the developing fetus, ACIP recommends that pregnancy be avoided for four weeks after receiving a live attenuated vaccine (MMR, varicella, live attenuated influenza, yellow fever). This interval may be shorter than that recommended by the manufacturer.

Last reviewed: August 29, 2022

CDC does not recommend Dengvaxia for non-residents of areas where dengue is endemic. If the child spends regular extended periods in Puerto Rico to point that they are considered a part-time resident, the family should consult with the child’s health care provider in Puerto Rico for assessment.

Last reviewed: January 17, 2025

The first two doses of Td are valid because they are separated by at least 4 weeks. However, the minimum interval between the second and third doses of tetanus-containing vaccine is 6 calendar months. So, the Td component of the Tdap dose is not valid because it was given only 4 months after the second dose. The pertussis component can be counted as valid. The patient should receive another dose of Td or Tdap 6 months after the invalid Tdap dose.

Last reviewed: March 31, 2022

Reporting of adequate and inadequate is acceptable only if your lab is using mIUs as the measurement for anti-HBs and the cutoff is below 10 mIU for reporting inadequate anti-HBs and 10 mIU or higher for reporting adequate anti-HBs. You should check with your lab to be certain this is being done.

Last reviewed: January 17, 2025

Every vaccine storage unit must have a temperature monitoring device (TMD). CDC recommends that vaccines be monitored using a “digital data logger” (DDL). A DDL provides the most accurate storage unit temperature information, including a detailed record of how long a unit has been operating outside the recommended temperature range (referred to as a “temperature excursion”). Unlike a simple minimum/maximum thermometer, which only shows the coldest and warmest temperatures reached in a unit, a DDL provides a log of the temperature recorded at preset intervals (at least every 30 minutes is recommended).

Many DDLs use a buffered temperature probe, which is the most accurate way to measure actual vaccine temperatures. Temperatures measured by a buffered probe match vaccine temperatures more closely than those measured by standard thermometers, which tend to reflect only air temperature. Temperature data from a DDL can either be downloaded to a computer using special software or retrieved from a website. The software or website may also allow you to set the frequency of temperature readings. Reviewing DDL data regularly is critical to ensure temperature excursions that could damage vaccines do not go on without being addressed. It is important to decide whether independent software or a website program works best for your facility.

Temperature monitoring devices that are NOT recommended include alcohol or mercury thermometers, even if placed in a fluid-filled, biosafe, liquid vial; bimetal stem devices; devices used for food; chart recorders; infrared devices; and devices that do not have a current and valid Certificate of Calibration Testing. Please note that some devices sold in hardware and appliance stores are designed to monitor temperatures for household food storage. They are not calibrated and not accurate enough to ensure vaccines are stored within the correct temperature range. Using these devices can pose a significant risk of damaging vaccines due to undetected out-of-range temperatures.

More details on temperature monitoring are available on pages 10–11 of CDC Vaccine Storage and Handling Toolkit, available at www.cdc.gov/vaccines/hcp/admin/storage/toolkit/storage-handling-toolkit.pdf. Additional details about temperature monitoring for COVID-19 and mpox vaccines are available in the addendum at the end of the toolkit.

Last reviewed: July 26, 2023

Although new HPV infections are most commonly acquired in adolescence and young adulthood, having a new sex partner at any age is a risk factor for acquiring a new HPV infection. In addition, some people have specific behavioral or medical risk factors for HPV infection or disease, including men who have sex with men, transgender people, and people with immunocompromising conditions. HPV vaccine works to prevent infection among people who have not been exposed to vaccine-type HPV before vaccination. A discussion with your patient is the best way to decide together how much the patient may benefit from HPV vaccination to prevent new HPV infections.

Last reviewed: March 2, 2024

PCV15 vaccine is recommended to be given first because this sequence provides the best immune response to both PCV15 and PPSV23 vaccine serotypes. An evaluation of immune response after a second pneumococcal vaccination administered 1 year after an initial dose showed that subjects who received PPSV23 as the initial dose had lower antibody responses to conjugate vaccine serotypes after subsequent administration of PCV13 than those who had received PCV13 as the initial dose followed by a dose of PPSV23. Lower antibody responses to conjugate vaccine serotypes were also seen in people 65 years and older who received PCV20 1 to 5 years after a dose of PPSV23 compared to those who received PCV20 at least 6 months after a dose of PCV13 or those who received PCV13 followed by PPSV23. PPSV23 is not recommended following administration of PCV20 or PCV21.

Last reviewed: November 13, 2024

In June 2024, ACIP updated its recommendations for RSV vaccination. ACIP routinely recommends  a single dose of any of the three licensed RSV vaccines for all adults age 75 years and older. ACIP also recommended a single dose of any RSV vaccine for adults age 60 through 74 years who are increased risk for serious RSV infection due to specific high risk conditions, frailty, or high-risk living arrangements (e.g., residents of long-term care facilities). Refer to the question and answer about high-risk conditions for which CDC recommends vaccination among adults age 60 through 74 years for the detailed list.

See current ACIP recommendation for older adults here: www.cdc.gov/acip-recs/hcp/vaccine-specific/rsv.html

Last reviewed: August 25, 2024

For people age 6 months through 64 years, CDC recommends any available age-appropriate influenza vaccine product.

For adults age 65 years and older, three influenza vaccines are preferentially recommended: Fluzone High-Dose (HD-IIV, Sanofi), Flublok recombinant (RIV, Sanofi), and Fluad adjuvanted (aIIV, CSL Seqirus). In June 2022, ACIP concluded that these three vaccines are potentially more effective than standard dose, unadjuvanted flu vaccines. However, if none of the three products are available, people age 65 years and older should get any other age-appropriate influenza vaccine.

Review the full explanation for the ACIP decision to prefer these products in this age group in the 2022 ACIP recommendations for influenza vaccination: www.cdc.gov/mmwr/volumes/71/rr/pdfs/rr7101a1-H.pdf.

ACIP recommends that solid organ transplant recipients (SOTRs) age 18 years through 64 years have the option of receiving HD-IIV or aIIV, both of which are licensed for people age 65 years or older. However, HD-IIV and aIIV are not preferentially recommended over age-appropriate influenza vaccine products for SOTRs.

Last reviewed: September 5, 2024

In general, no. According to ACIP’s “General Best Practice Guidelines for Immunization”, concerns about spacing between doses of live vaccines not given at the same visit applies only to live injectable or intranasal vaccines. So, live oral cholera vaccine may be administered simultaneously with another vaccine, or at any interval before or after administration of another vaccine. There is one exception: ACIP recommends (based upon expert opinion) that live oral cholera vaccine should be administered at least 8 hours before the first dose of live oral Ty21a typhoid vaccine in order to minimize the risk that the oral cholera vaccine buffer might interfere with the enteric coating of the oral Ty21a vaccine.

Last reviewed: June 6, 2023

Infants who will travel outside the United States should be up to date for all routinely recommended vaccines. One dose of MMR is recommended for infants age 6 through 11 months before international travel. This dose does not count toward the two doses needed to complete the childhood schedule. Infants 6 through 11 months of age traveling to an area at risk for hepatitis A exposure also should receive a dose of hepatitis A vaccine. This dose does not count toward the two doses needed to complete the childhood schedule. Infants younger than age 12 months traveling to a hepatitis A endemic area are not recommended to receive immune globulin for prevention of hepatitis A because immune globulin could interfere with the response to MMR. Varicella vaccine is not recommended before age 12 months, even for travelers. For other vaccine recommendations for travelers, consult the CDC travel website at wwwnc.cdc.gov/travel/.

Last reviewed: January 20, 2025

Reports can be submitted online through the VAERS website or by completing and uploading a writable PDF VAERS report form. Both options can be accessed on the VAERS website at vaers.hhs.gov/reportevent.html. If you need further assistance with reporting to VAERS, please email info@VAERS.org or call 1-800-822-7967.

Last reviewed: August 31, 2022

Most reactions to this vaccine are mild, such as soreness and redness at the injection site. Moderate problems, including hives, pain in the joints, and fever, are possible in a small percentage of patients (6%) given booster doses. Once initiated, rabies prophylaxis should not be interrupted or discontinued because of local or mild systemic adverse reactions to rabies vaccine. Usually, such reactions can be successfully managed with anti-inflammatory and antipyretic agents, such as ibuprofen or acetaminophen.

Last reviewed: May 14, 2023

Yes.

Last reviewed: July 23, 2023

Residence in a homeless shelter or halfway house is considered a high-risk indication only for hepatitis A vaccination because of the increased risk of hepatitis A exposure and serious illness among people experiencing homelessness or living in temporary housing. In all other respects, recommendations for vaccinating adult residents would be the same as those for all adults on the ACIP adult immunization schedule. Residents with medical conditions identified on Table 2 of the schedule should be vaccinated according to that table.

Any residents 18 or younger should be vaccinated according to the catch-up recommendations on the ACIP child/teen immunization schedule. People age 19 through 21 years are not recommended routinely to receive MenACWY. MenACWY may be administered through age 21 years as a catch-up vaccination for those who have not received a dose after their 16th birthday.

Last reviewed: November 15, 2024

Yes. For everyone whose varicella immunity is based on vaccination, 2 doses of varicella vaccine are recommended.

Last reviewed: May 16, 2023

Yes. On rare occasions, HAV infection has been transmitted by transfusion of blood or blood products collected from donors during the viremic phase of their infection (i.e., when HAV is in the donor’s blood). Since 2002, tests to detect the presence of hepatitis A virus RNA in donated plasma have drastically reduced the risk of hepatitis A transmission from products derived from blood plasma.

Last reviewed: June 25, 2023

It is important to know the federal requirements for documenting the vaccines administered to your patients. The requirements are defined in the National Childhood Vaccine Injury Act (NCVIA) enacted in 1986. The law applies to all routinely recommended childhood vaccines, and vaccines recommended during pregnancy (except COVID-19 and RSV), regardless of the age of the patient receiving the vaccines.

The RSV preventive antibody, nirsevimab (Beyfortus, Sanofi) is not a vaccine and not covered by the NCVIA, but a VIS-equivalent, known as an immunization information sheet (IIS), should be provided to the caregiver of an infant receiving nirsevimab.

The following information must be documented on the patient’s paper or electronic medical record or on a permanent office log when a vaccine covered by the NCVIA is given, and is recommended when any vaccine is administered:

  1. The vaccine manufacturer
  2. The lot number of the vaccine
  3. The date the vaccine is administered
  4. The name, office address, and title of the healthcare provider administering the vaccine
  5. The Vaccine Information Statement (VIS) edition date located in the lower right corner on the back of the VIS; when administering combination vaccines, all applicable VISs should be given and the individual VIS edition dates recorded
  6. The date the VIS is given to the patient, parent, or guardian

The federally required information should be both permanent and accessible.

Federal law does not require a parent, patient, or guardian to sign a consent form in order to receive a vaccination; providing them with the appropriate VIS(s), IIS, or Emergency Use Authorization (EUA) Fact Sheet (where applicable) and answering their questions is sufficient under federal law.

Last reviewed: February 16, 2025

Healthy adolescents who are not at increased risk for meningococcal B disease should receive 2 doses of Trumenba (MenB-FHbp, Pfizer) or Bexsero (MenB-4C, GSK) administered at 0 and 6 months. If the second dose is given at an interval of less than 6 months, a third dose should be given at least 4 months after the 2nd dose.

For people age 10 years and older at increased risk for meningococcal B disease, 3 doses of Trumenba or Bexsero should be administered at 0, 1–2, and 6 months. The 3-dose series should be used for all people with functional or anatomic asplenia, people with persistent complement component deficiency (an immune system disorder) or those who take a complement inhibitor (examples include eculizumab [Soliris], ravulizumab [Ultomiris], and sutimlimab [Sanofi]), microbiologists who work with meningococcal isolates in a laboratory, and people exposed during serogroup B outbreaks.

Penbraya (MenABCWY, Pfizer) contains MenB-Fhbp (Trumenba) and is FDA-licensed for ages 10 through 25 years as a two-dose series, given 6 months apart, for vaccination against all 5 serogroups. For adolescents or adults not at increased risk for meningococcal disease, if Penbraya is used for dose 1 of MenB, Trumenba should be administered for the second dose of MenB. For people age 10 years or older (including those older than age 25 years) at increased risk of meningococcal disease, ACIP recommends that 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.

Last reviewed: November 15, 2024


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Last reviewed: August 11, 2024

Use of DTaP-IPV solution as the diluent for the Hib component is specifically written both on the Pentacel box AND on the DTaP-IPV vial label. The DTaP-IPV component will count as valid doses of DTaP and IPV vaccines, but you should take measures to prevent this error in the future. You cannot mix the Hib component with sterile water. ActHib must ONLY be reconstituted with either the DTaP-IPV solution supplied with Pentacel, or with a specific ActHib saline diluent. If you have a vial of lyophilized ActHib but neither diluent, you must contact the manufacturer (Sanofi) and obtain ActHib diluent.

Last reviewed: January 21, 2025

Infants for whom the first dose of rotavirus vaccine was inadvertently administered at age 15 weeks or older should receive the remaining doses of the series at the routinely recommended intervals. Timing of the first dose should not affect the safety and efficacy of the remaining doses. Rotavirus vaccine should not be given after age 8 months 0 days even if the series is incomplete.

Last reviewed: June 7, 2023

Dengvaxia is a live-attenuated vaccine. Live virus vaccines are generally not recommended during pregnancy; however, people infected with DENV during pregnancy are at increased risk of severe dengue. Perinatal transmission may occur with peripartum maternal infection increasing the risk of symptomatic illness in the newborn. The ACIP recommendations classify pregnancy as a precaution to vaccination with Dengvaxia.

Pregnant people were not explicitly enrolled and studied in the Dengvaxia vaccine trials. A minimal number of pregnant women in the trial inadvertently received Dengvaxia. There was no increased frequency of adverse pregnancy outcomes (e.g., spontaneous abortion, intrauterine death, stillbirth) noted compared to the control group. However, due to the small sample size, no conclusions can be made on the possible effect of Dengvaxia on pregnancy.

Providers should consider the pregnant person’s risk of DENV infection and its complications when deciding whether or not to recommend Dengvaxia during pregnancy or to defer until after pregnancy.

Last reviewed: January 17, 2025

All inactivated vaccines, including COVID-19 vaccines, can be given on the same day, or on any day before or after giving other inactivated or live vaccines. Early guidance from ACIP recommended against coadministration of COVID-19 vaccines with other vaccinations; however, ACIP updated its guidance in mid-2021 to state that these vaccines may be coadministered with other vaccinations when necessary.

If two live vaccines are not given on the same day, they need to be spaced at least 4 weeks apart. If both pneumococcal conjugate vaccine (PCV) and 23-valent pneumococcal polysaccharide vaccine (PPSV23) are indicated for a high-risk patient, these vaccines should not be given at the same visit. The PCV 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 PCV to avoid interference between the 2 vaccines. A person with anatomic or functional asplenia should receive both PCV and meningococcal conjugate vaccines (MenACWY). If Menactra brand MenACWY is used the person should first receive all recommended doses of PCV then Menactra at least 4 weeks later. Menveo or MenQuadfi brands of MenACWY can be given at the same time or at any time before or after PCV.

Last reviewed: December 28, 2022

There are two circumstances when a third dose of MMR is recommended. ACIP recommends that women of childbearing age who have received 2 doses of rubella-containing vaccine and have rubella serum IgG levels that are not clearly positive should receive 1 additional dose of MMR vaccine (maximum of 3 doses). Further testing for serologic evidence of rubella immunity is not recommended. MMR should not be administered to a pregnant woman.

In 2018, ACIP published guidance for MMR vaccination of people at increased risk for acquiring mumps during an outbreak. People previously vaccinated with 2 doses of a mumps virus–containing vaccine who are identified by public health authorities as being part of a group or population at increased risk for acquiring mumps because of an outbreak should receive a third dose of a mumps virus–containing vaccine (MMR or MMRV) to improve protection against mumps disease and related complications. More information about this recommendation is available at www.cdc.gov/mmwr/volumes/67/wr/pdfs/mm6701a7-H.pdf.

Last reviewed: June 19, 2023

The routinely recommended minimum age for Shingrix among immunocompetent adults is 50 years. However, if a dose is inadvertently administered to an immunocompetent adult 18 through 49 years of age CDC does not recommend repeating the dose. The second Shingrix dose should not be administered until the 50th birthday. This guidance does not appear in the most recent zoster ACIP statement but is in the General Best Practices Guidance (Table 3-1 in the Timing and Spacing of Immunobiologics section at www.cdc.gov/vaccines/hcp/acip-recs/general-recs/timing.html) and is based on guidance from CDC’s zoster subject matter experts.

Among people who are or will be immunosuppressed or immunodeficient due to disease or therapy, the minimum age for vaccination is 19 years.

Last reviewed: March 9, 2022

While administration of Pentacel to a 5-year-old would be considered off-label and a vaccine administration error, the doses of DTaP and IPV can be counted as valid and do not need to be repeated. Hib vaccine is not routinely administered after a child has reached the age of 5 years so it is also a vaccine administration error. You should explain this error to the parents and assure them that the extra Hib dose will cause no harm.

Last reviewed: January 27, 2025

Having a pregnant person in a household, including the child’s mother, is not a contraindication to administration of any routinely recommended vaccine. Pregnant people should not have close contact with anyone who has recently (within the last 28 days) received the live, replication-competent smallpox vaccine (ACAM2000, Emergent Biosolutions).

Last reviewed: August 29, 2022

If the first dose of a tetanus toxoid-containing vaccine is administered before the first birthday, 4 doses are necessary before beginning the 10-year cycle of booster doses. If the first dose is administered after the first birthday, 3 doses are necessary. The final dose should be spaced 6 months from the previous dose.

Last reviewed: March 31, 2022

Most likely this person has a resolved HBV infection and is immune. However, it would be preferable to test her again for all these serologic markers, and also quantify the anti-HBs result. If the results are still positive for anti-HBc, and anti-HBs is less than the immune level of 10 mIU/mL, you can give her one dose of HepB vaccine and test again in 1–2 months. If the anti-HBs is positive (10 mIU/mL or higher), she is immune. No further action is needed other than to document the results. If the anti-HBs is still negative, complete the vaccine series and test again 1–2 months after the last dose of vaccine.

Last reviewed: January 17, 2025

CDC recommends that you use only a temperature monitoring device (TMD) with a Certificate of Calibration Testing (also known as a Report of Calibration). This certificate provides the TMD’s level of accuracy compared to a recognized standard. This certificate comes with the TMD when it is purchased, and it is different than the manufacturer’s warranty. While all TMDs are calibrated during manufacturing, certified calibrated TMDs undergo a second individual calibration against a reference standard from an accredited testing laboratory. Calibration testing should be done every 2 to 3 years or according to the manufacturer’s suggested timeline to ensure the accuracy of the device continues to conform to nationally accepted standards. Additional information on this topic is available on page 11 of CDC’s Vaccine Storage and Handling Toolkit, available at www.cdc.gov/vaccines/hcp/admin/storage/toolkit/storage-handling-toolkit.pdf.

Last reviewed: July 26, 2023

Because HPV acquisition generally occurs soon after first sexual activity, vaccine effectiveness will be lower in older age groups as a result of prior infections. In general, exposure to HPV also decreases among individuals in older age groups. Evidence suggests that although HPV vaccination is safe for adults 27 through 45 years, population benefit would be minimal; nevertheless, some adults who are unvaccinated or incompletely vaccinated might be at risk for new HPV infection and might benefit from vaccination in this age range.

Last reviewed: March 2, 2024

NCVIA requirements apply to diphtheria, tetanus, pertussis, measles, mumps, rubella, polio, hepatitis A, hepatitis B, Haemophilus influenzae type b (Hib), varicella, seasonal influenza (inactivated and live attenuated), pneumococcal conjugate, meningococcal, rotavirus, and human papillomavirus (HPV) vaccine.

Last reviewed: February 16, 2025

In 2000, the first pneumococcal conjugate vaccine (PCV) was licensed in the U.S. This vaccine contained seven serotypes (4, 6B, 9V, 14, 18C, 19F, and 23F) of Streptococcus pneumoniae and became known as PCV7 (Prevnar by Wyeth, now Pfizer). Ten years later in February 2010, a new 13-valent product was licensed — PCV13 (Prevnar 13, Pfizer) — which added 6 new serotypes (1, 3, 5, 6A, 7F, and 19A). Together, these 13 serotypes accounted for the majority of invasive pneumococcal disease (IPD) in the U.S. at the time, including serotype 19A, which is the most common IPD-causing serotype in young children. In February 2010 ACIP recommended that healthcare providers transition from use of PCV7 to use of PCV13 for routine vaccination of children.

PCV7 was initially recommended for routine use in infants and children ages 2 through 59 months. The recommendations were expanded with the licensure of PCV13 to include vaccination of children age 60 through 71 months with underlying medical conditions, and also vaccination of older children, ages 6 through 18 years, with medical conditions placing them at increased risk of invasive pneumococcal disease.

PCVs were further updated with licensure for use in children of PCV15 in 2022 and PCV20 in 2023.

Last reviewed: November 13, 2024

Because of the strong association between the risk of severe RSV disease and age, ACIP recommends RSV vaccination of all adults age 75 years or older. ACIP has specified several conditions as reasons for RSV vaccination before age 75 years (age 60 through 74 years) due to their association with a high risk of hospitalization with severe RSV disease compared to otherwise healthy adults of the same age. These conditions are similar to, but not the same as, high-risk conditions specified for pneumococcal or influenza vaccination. An individual’s risk is increased further if they have more than one of the conditions.

  • Non-immunocompromising chronic health conditions:
    • Chronic cardiovascular disease (such as heart failure, coronary artery disease, or congenital heart disease [excluding isolated hypertension])
    • Chronic lung disease (such as chronic obstructive lung disease [COPD], emphysema, asthma, interstitial lung disease, or cystic fibrosis)
    • End-stage kidney disease or dependence on hemodialysis or other renal replacement therapy
    • Diabetes mellitus complicated by chronic kidney disease, neuropathy, retinopathy, or other end-organ damage, or requiring treatment with insulin or sodium-glucose cotransporter-2 (SGLT2) inhibitor
    • Severe obesity (measured as a body mass index of 40 kilograms per meter squared or greater)
    • Chronic liver disease (such as cirrhosis)
    • Neurologic or neuromuscular conditions causing impaired airway clearance or respiratory muscle weakness (such as poststroke dysphagia [swallowing dysfunction], amyotrophic lateral sclerosis [ALS], or muscular dystrophy [excluding history of stroke without impaired airway clearance])
    • Chronic blood disorders (such as sickle cell disease, thalassemia)
  • Moderate or severe immune compromise (due to a medical condition or due to immunosuppressive medications or treatment)
  • Overall frailty (based on an assessment of frailty)
  • Residence in a nursing home or other long-term care facility
  • Other chronic medical conditions or risk factors not specified in this list that a healthcare provider determines might increase the risk of severe disease due to RSV respiratory infection

People age 60 through 74 years who do not have a medical condition or risk factor that increases their risk of severe RSV disease are not recommended to receive RSV vaccine: they should wait to be vaccinated until a high-risk condition develops or until they turn 75, whichever comes first.

 

Last reviewed: August 25, 2024

Immunity is not considered lifetime, however, CDC does not currently have any recommendation related to revaccination with oral cholera vaccine. The duration of immunity beyond the 3-month period of clinical trial evaluation in people age 18 through 45 years following one dose is unknown. As more information becomes available, CDC will update its recommendations accordingly.

Last reviewed: June 6, 2023

Yes. Any occurrence of medical significance warrants a VAERS report. VAERS looks for trends, so such information is helpful. You can obtain more information about VAERS at vaers.hhs.gov or by calling (800) 822-7967.

Last reviewed: August 31, 2022

The rabies vaccine is not recommended for routine use in the general population. Anyone for whom the pre-exposure vaccine is recommended should not receive a dose when they are moderately or severely ill.

Last reviewed: May 14, 2023

There are no severe reactions known to occur following IPV.

Last reviewed: July 23, 2023

No. There are no acceptable serologic titers that can be used as evidence of protection against meningococcal A, C, W, and Y disease. In addition, the immunologic studies used for licensing purposes (serum bactericidal assay, SBA) are likely different from the serologic titers obtained at a doctor’s office (IgG antibody, for example). It is not clear what sort of testing is shown in the results you sent. However, even if SBA results are available, they cannot be used to assess whether there is a level of protection at the individual level.

Last reviewed: November 15, 2024

In the ten years following vaccine licensure in 1995, there was a significant decline in varicella disease, as well as varicella-related hospitalizations and deaths. Although a 1-dose regimen was estimated to be 80% to 85% effective, breakthrough disease was still occurring in highly vaccinated populations. A 2-dose regimen was adopted in 2006 to further reduce the risk of disease among vaccinated people whose numbers would accumulate over time, which could lead to varicella disease later in life when it can be more severe.

Last reviewed: May 16, 2023

In experimentally infected nonhuman primates, HAV has been detected in saliva during the incubation period; however, transmission by human saliva has not been reported.

Last reviewed: June 25, 2023

No. The 3-dose series (at 0, 1–2 and 6 months) is intended to rapidly induce immunity to serogroup B meningococcal bacteria. If a microbiologist or other person at increased risk has received 2 doses of Trumenba or Bexsero separated by 6 months, then their primary vaccine series is considered complete. This microbiologist will need his first booster dose 1 year after the final dose of the primary series, then a booster dose every 2 to 3 years, as long as he remains at increased risk. Use the same type of MenB vaccine for all primary series and booster doses.

Last reviewed: November 15, 2024

ACIP does not recommend routine Hib vaccination of healthy children 60 months of age or older, even if they have no prior history of Hib vaccination.

Last reviewed: January 21, 2025

Due to the variety of causes and consequences of altered immunocompetence, and limited studies of vaccination with these conditions, vaccination recommendations for primary and secondary immunodeficiencies are generally based upon expert opinion.

CDC’s “General Best Practices for Immunization” includes a subsection for vaccine recommendations for people with altered immunocompetence here: www.cdc.gov/vaccines/hcp/imz-best-practices/altered-immunocompetence.html. For a summary of specific vaccine recommendations for people with different types of primary and secondary immunodeficiencies, refer to Table 8-1 at that site.

Last reviewed: January 20, 2025


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Last reviewed: December 6, 2024

CDC specifies for RSV vaccination the same moderate to severe immunocompromising conditions that require additional doses of COVID-19 vaccines. Below is the CDC description from its website (www.cdc.gov/vaccines/covid-19/clinical-considerations/interim-considerations-us.html#immunocompromised).

Moderate and severe immunocompromising conditions and treatments include but are not limited to:

  • Active treatment for solid tumor and hematologic malignancies
  • Hematologic malignancies associated with poor responses to COVID-19 vaccines regardless of current treatment status (e.g., chronic lymphocytic leukemia, non-Hodgkin lymphoma, multiple myeloma, acute leukemia)
  • Receipt of solid-organ transplant or an islet transplant and taking immunosuppressive therapy
  • Receipt of chimeric antigen receptor (CAR)-T-cell therapy or hematopoietic cell transplant (HCT) (within 2 years of transplantation or taking immunosuppressive therapy)
  • Moderate or severe primary immunodeficiency (such as common variable immunodeficiency disease, severe combined immunodeficiency, DiGeorge syndrome, or Wiskott-Aldrich syndrome)
  • Advanced HIV infection (people with HIV and CD4 cell counts less than 200 per cubic milliliter, history of an AIDS-defining illness without immune reconstitution, or clinical manifestations of symptomatic HIV) or untreated HIV infection
  • Active treatment with high-dose corticosteroids (i.e., 20 mg or more of prednisone or equivalent per day when administered for 2 or more weeks), alkylating agents, antimetabolites, transplant-related immunosuppressive drugs, cancer chemotherapeutic agents classified as severely immunosuppressive, tumor necrosis factor (TNF) blockers, and other biologic agents that are immunosuppressive or immunomodulatory (e.g., B-cell-depleting agents)

Factors to consider in assessing the general level of immune competence in a patient include disease severity, duration, clinical stability, complications, comorbidities, and any potentially immune-suppressing treatment.

For additional information about the degree of immune suppression associated with different medical conditions and treatments, refer to the CDC General Best Practice Guidelines for Immunizations section on altered immunocompetence (www.cdc.gov/vaccines/hcp/imz-best-practices/altered-immunocompetence.html).

Last reviewed: August 25, 2024

No. RSV vaccination is not recommended for people his age with hypertension and no other risk conditions. People age 60 through 74 years who do not have a medical condition or risk factor that increases their risk of severe RSV disease are not recommended to receive RSV vaccination at this time.

Last reviewed: August 25, 2024

In response to public health emergencies and security dangers, the government supports the development of countermeasures. A countermeasure is a vaccine, medication, device, or other item used to prevent, diagnose, or treat a public health emergency or a security threat.

The Countermeasures Injury Compensation Program (CICP, www.hrsa.gov/cicp) provides compensation for covered serious injuries or deaths that occur as the result of the administration or use of certain countermeasures. Compensation may include unreimbursed medical expenses (expenses that health insurance did not cover), lost employment income, and the survivor death benefit. The Secretary of the Department of Health and Human Services has issued federal declarations under the Public Readiness and Emergency Preparedness Act (PREP Act) that list the countermeasures covered by the CICP. For a list of covered countermeasures and for information about filing a claim, visit www.hrsa.gov/cicp/covered-countermeasures.

Last reviewed: February 16, 2025


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Last reviewed: December 6, 2024

A buffered temperature probe is designed to prevent misleading and rapidly fluctuating readings by protecting the TMD from sudden changes in air temperature that can occur when opening a refrigerator door. A probe is “buffered” by immersing it in a vial filled with liquid (e.g., glycol, ethanol, glycerin), loose media (e.g., sand, glass beads), or a solid block of material such as Teflon or aluminum. Vaccine packaging is more thermostable than air because the temperature of solids and fluids change more slowly than air. Standard probes that measure air temperature can fluctuate with the defrost cycles of the unit, frequent opening and closing the door on busy workdays, air circulation patterns, etc. This could lead someone to inaccurately interpret changes in air temperature to mean that the vaccine temperature was out of range.

Last reviewed: July 26, 2023

All vaccines except the live, replication-competent smallpox vaccine (ACAM2000, Emergent Biosolutions) and yellow fever vaccine may be given to people who are breastfeeding.

ACAM2000 is contraindicated due to the theoretical risk of contact transmission of the vaccine virus from mother to child.

The only yellow fever (YF) vaccine licensed in the United States (YF-Vax, Sanofi) is contraindicated in people who are breastfeeding infants younger than 9 months of age. There have been three case reports of YF vaccine-associated encephalitis in infants under one month of age who were being exclusively breastfed at the time the mother received YF vaccine. ACIP currently recommends that people who are breastfeeding should be advised to postpone travel to YF endemic or epidemic regions; however, if travel cannot be avoided or postponed, the breastfeeding parent should receive YF vaccine. Although there are no data, some experts recommend that breastfeeding people who receive YF vaccine should temporarily suspend breastfeeding, pump, and discard pumped milk for at least 2 weeks after vaccination before resuming breastfeeding.

Last reviewed: August 29, 2022

CDC recommends that Dengvaxia should be used with precaution in breastfeeding individuals. There are no data in humans to evaluate the safety of Dengvaxia in infants who are breastfed. Providers and breastfeeding parents should weigh the benefits of breastfeeding and the risk of DENV infection in the mother and the infant.

Last reviewed: January 17, 2025

Simultaneous means the same day—the same clinic day. If someone receives a vaccine in the morning and then another that same afternoon, it would be considered simultaneous administration.

Last reviewed: December 28, 2022

MMR vaccine given within 72 hours of initial measles exposure can reduce the risk of getting sick or reduce the severity of symptoms. Another option for exposed, measles-susceptible individuals at high risk of complications who cannot be vaccinated is to give immunoglobulin (IG) within six days of exposure. Do not administer MMR vaccine and IG simultaneously, as the IG invalidates the vaccine.

Information on post-exposure prophylaxis for measles can be found in the 2013 ACIP guidance at www.cdc.gov/mmwr/pdf/rr/rr6204.pdf, page 24.

Last reviewed: June 19, 2023

No. The vaccine series need not be restarted if more than 6 months have elapsed since the first dose.

Last reviewed: March 9, 2022

For most people who need only 1 dose of influenza vaccine, vaccination should ideally be offered in September and October. For people not vaccinated by the end of October, vaccination efforts should continue as long as influenza viruses are circulating and unexpired vaccine is available.

Vaccination in July and August should be avoided for most groups unless there is concern that vaccination later in the season might not be possible. Early vaccination has been associated with waning of vaccine-induced immunity and decreased vaccine effectiveness before the end of the influenza season, particularly among older adults.

Vaccination in July and August may be considered for people in their third trimester of pregnancy, to allow time for protective maternal antibodies to transfer to the fetus, providing protection during early infancy. Children younger than age 9 years who need two doses of vaccine this season should receive their first dose as soon as possible so that they can get their second dose before the end of October. Children who need only one dose can be considered for vaccination in July or August.

Last reviewed: August 11, 2024

As of January 2020, ACIP recommends that Td or Tdap may be administered in any situation when only Td vaccine was previously recommended. Someone who received a dose of Tdap at age 11 or 12 years should receive a booster dose of Td or Tdap vaccine ten years later, unless tetanus prophylaxis is required sooner due to an injury or if Tdap vaccination is needed during pregnancy.

Last reviewed: March 31, 2022

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