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.

How to Find Your Answer

Note: Selecting a filter subcategory may also return results from the primary category. We are working with our vendor to resolve this error.

  • Some filter options may become disabled as you narrow your selections.
  • Filters are easily added and removed. Click or tap on the X to remove individual filters or choose “Reset All Filters” to remove all filters.
Results (1355)

You are correct that vaccinated people can still be infected with viruses or bacteria against which they are vaccinated. No vaccine is 100% effective. Vaccine effectiveness varies from greater than 95% (for diseases such as measles, rubella, and hepatitis B) to much lower (60% for influenza in years with a good match of circulating and vaccine viruses, and 70% for acellular pertussis vaccines in the 3-5 years after vaccination). More information is available for each vaccine and disease at www.cdc.gov/vaccines/by-disease/ and www.immunize.org/vaccines.

Last reviewed: June 19, 2023

A history of genital warts or clinically evident genital warts indicates previous infection with HPV, most often type 6 or 11, which cause 90% of genital warts. However, people with this history might not have been infected with both HPV 6 and 11 or with the other HPV types included in HPV vaccine. Vaccination will provide protection against infection with HPV serotypes the patient has not already acquired. Providers should advise their patients/clients that the vaccine will not have a therapeutic effect on existing HPV infection or genital warts. It is important, however, that patients receive a full age-appropriate series of HPV vaccine to get full protection from genital warts, in addition to the cancer-causing HPV types in the vaccine.

Last reviewed: March 2, 2024

Yes. MenB vaccines work differently and receiving mismatched MenB doses might result in inadequate protection. For this reason, documentation of the brand of vaccine (the two MenB products are Bexsero [MenB-4C] and Trumenba [MenB-FHbp]) is especially important. If a patient at high risk requires a booster dose and the brand of the primary series doses cannot be determined or is unavailable, then CDC recommends restarting the primary series with the available brand.

The first booster dose is recommended one year following completion of the primary series with subsequent booster doses every 2–3 years thereafter, as long as risk remains.

If a record shows that Penbraya (MenABCWY, Pfizer) was administered to a patient, this combination product contains MenB-FHbp (Trumenba) as its MenB component and subsequent doses should be Trumenba (or Penbraya, if indicated).

Last reviewed: March 24, 2024

People who have had PCV13 and PPSV23 after the 65th birthday are not routinely recommended to receive additional doses of pneumococcal vaccine; however, they may receive a dose of PCV20 or PCV21 at least 5 years after their most recent pneumococcal vaccination based on shared clinical decision-making. The benefit of PPSV23 wanes after about 5 or more years. Considerations for PCV20 or PCV21 in this situation include the patient’s overall health and risk of pneumococcal disease, their desire to be protected, and time since last pneumococcal vaccination.

Last reviewed: November 13, 2024

Yes. Breastfeeding is not a contraindication for any routine vaccination including FluMist (LAIV).

Last reviewed: August 11, 2024

Clinical trials of nirsevimab (Beyfortus, Sanofi) in infants less than 8 months old born during or entering their first RSV season showed that giving nirsevimab reduced the risk of RSV-associated lower respiratory tract infection (LRTI) requiring a medical visit or hospitalization by approximately 80 percent and reduced the risk of ICU admission for this reason by 90 percent.

Clinical trials did not study hospitalization rates among older infants and toddlers at high risk of severe RSV disease in their second RSV season. Instead, a study was done to measure blood levels of nirsevimab given to infants and toddlers at increased risk for severe RSV disease (certain preterm infants and those with serious heart or lung disease). The blood levels of nirsevimab were equivalent to the levels in healthy infants in the clinical trial who received nirsevimab in their first RSV season. Based on this finding, it is estimated that their protection from serious infection would also be similar.

Last reviewed: August 25, 2024


2:02

View All Video Questions

Last reviewed: May 9, 2023


1:21

View All Video Questions

Last reviewed: April 21, 2023

With rare exceptions, yes. Like other live vaccines, FluMist (LAIV) should not be administered to immunosuppressed people. ACIP has stated a preference for using injectable influenza vaccine for all close contacts of severely immunosuppressed individuals during those periods in which the immunosuppressed person requires care in a protective environment because of the theoretical risk that the live attenuated vaccine virus could be transmitted to the severely immunosuppressed individual and cause disease. Healthcare personnel or other people who have close contact with people with lesser degrees of immunosuppression (people who do not require a protective environment such as reverse isolation in a hospital setting) who are otherwise eligible for FluMist may receive it. No special precautions need to be taken by the vaccinated person.

Last reviewed: August 11, 2024


1:23

View All Video Questions

Last reviewed: May 9, 2023

Timing of vaccination should be evaluated on a case-by-case basis. When possible, patients should be vaccinated before becoming immunosuppressed. If vaccination before initiating immunosuppressive treatment is feasible, a shortened interval of 4 weeks between doses 1 and 2 may be considered. If vaccination before immunosuppression is not possible, providers should consider timing vaccination when the immune response is likely to be most robust.

For additional information about timing of vaccination and specific conditions, see CDC’s Clinical Considerations for the Use of Recombinant Zoster Vaccines in Immunocompromised Adults Aged ≥ 19 Years: www.cdc.gov/shingles/vaccination/immunocompromised-adults.html#clinical-guidance.

Last reviewed: March 9, 2022

Postvaccination serologic testing for varicella immunity is not recommended in any group, including healthcare personnel.

Last reviewed: May 16, 2023

It is acceptable to put the Beyond Use Date (BUD) on the packaging; this may help when reviewing inventory. But a provider should always read the label on the vial before administering a vaccine. It is possible for a vial to be placed in the wrong box. So, the vial label is the safest place to put the BUD. Vial labels are small, and it may require putting an extra sticky label on the vial.

Last reviewed: July 26, 2023

Twinrix is an inactivated combination vaccine containing both hepatitis A virus (HAV) and HBV antigens. The vaccine contains 720 EL.U. of hepatitis A antigen (half of the Havrix adult dose) and 20µg of hepatitis B antigen (the full Engerix-B adult dose). In the U.S., Twinrix is licensed for use in people who are age 18 years or older. It can be administered to people who are at risk for both hepatitis A and hepatitis B, such as certain international travelers, people with chronic liver disease, men who have sex with men, illegal drug users, or to people who simply want to be immune to both diseases. A Twinrix series consists of 3 doses given intramuscularly on a 0, 1, and 6 month schedule.

Last reviewed: July 15, 2023

Vaccines received before starting chemotherapy generally do not need to be repeated after chemotherapy is completed. Chemotherapy does not negate vaccine-induced immunity. However, revaccination is recommended for people who are recipients of a hematopoietic cell transplant (HCT), such as a bone marrow transplant, because immunity present before the transplant is lost and may not be replaced by donor cells. For more information on this issue please refer to the Altered Immunocompetence section of the ACIP “General Best Practices Guidelines for Immunization” at www.cdc.gov/vaccines/hcp/acip-recs/general-recs/immunocompetence.html.

Last reviewed: August 29, 2022

Updated ACIP recommendations for the use of Tdap were published in April 2018 (available at www.cdc.gov/mmwr/volumes/67/rr/pdfs/rr6702a1-H.pdf) and January 2020 (available at www.cdc.gov/mmwr/volumes/69/wr/pdfs/mm6903a5-H.pdf). ACIP recommends that all adults age 19 years and older who have not yet received a dose of Tdap receive a single dose. Tdap should be administered regardless of interval since the last tetanus or diphtheria toxoid-containing vaccine (e.g., Td). After receiving Tdap, people should receive Td or Tdap every 10 years for routine booster immunization against tetanus and diphtheria, according to previously published guidelines. A dose of Tdap should be administered during each pregnancy, preferably early in the 27 week through 36 week gestation time period.

Providers should not miss an opportunity to vaccinate adults age 65 and older with Tdap. Providers may administer any Tdap vaccine they have available. When feasible, providers should administer Boostrix (GSK) to adults age 65 and older as it is licensed for this age group. Adacel (Sanofi) is licensed for use in people age 10 through 64. However, ACIP concluded that either vaccine administered to a person age 65 or older is immunogenic and will provide protection. A dose of either vaccine is considered valid.

When a tetanus toxoid-containing vaccine is needed for wound management in a person who has not previously received Tdap, the use of Tdap is preferred over Td.

Last reviewed: March 31, 2022

The 2020 ACIP recommendations for the prevention of hepatitis A define a person experiencing homelessness as 1) a person who lacks housing (regardless of whether the person is a member of a family), including a person whose primary residence during the night is a supervised public or private facility (e.g., shelter) that provides temporary living accommodations and a person who is a resident in transitional housing, 2) a person without permanent housing who might: live on the streets, stay in a shelter, mission, single-room occupancy facility, abandoned building, vehicle, or any other unstable or nonpermanent situation, or 3) who is “doubled up”, a term that refers to a situation where persons are unable to maintain their housing situation and are forced to stay with a series of friends or extended family members. In addition, previously homeless persons who are to be released from a prison or a hospital might be considered homeless if they do not have a stable housing situation to which they can return. The instability of a person’s living arrangements is critical to the definition of homelessness.

Last reviewed: June 25, 2023

The January 2018 recommendations are available at www.cdc.gov/mmwr/volumes/67/rr/pdfs/rr6701-H.PDF.

Last reviewed: July 21, 2023

All live injected vaccines (MMR, varicella, and yellow fever) are recommended to be given subcutaneously (Subcut). In February 2023, FDA approved the administration of MMRII (Merck) brand of MMR by either Subcut or IM routes. The Priorix (GSK) brand of MMR is approved only for Subcut administration. Intramuscular (IM) administration of any of these live virus vaccines is not likely to decrease immunogenicity, and doses given IM do not need to be repeated. When administering MMRII by the IM route, select an appropriate needle length for the patient’s size. See Immunize.org’s clinical resource “Administering Vaccines: Dose, Route, Site, and Needle Size” at www.immunize.org/catg.d/p3085.pdf.

Last reviewed: June 19, 2023

The ACIP discourages the practice of prefilling vaccine into syringes, primarily because of the increased possibility of administration and dosing errors. An exception may be considered when only a single type of vaccine is to be administered during a clinic (e.g., influenza). Another reason to discourage the practice in general is that some vaccines have a very limited shelf life after reconstitution. If the reconstituted vaccine is not used within the designated time period, it must be discarded. A chart of the time allowed between reconstitution and use, “Vaccines with Diluents: How to Use Them,” is available at www.immunize.org/catg.d/p3040.pdf. For more information on prefilling syringes, please read www.immunize.org/technically-speaking/20110901.asp.

Last reviewed: December 28, 2022

ACIP recommends a routine 2-dose HPV vaccine schedule for adolescents who start the vaccination series before the 15th birthday. The two doses should be separated by 6 to 12 months. The minimum interval between doses is 5 calendar months.

A 3-dose schedule is recommended for people who start the series on or after the 15th birthday and for people with certain immunocompromising conditions (such as cancer, HIV infection, or taking immunosuppressive drugs), regardless of their age at the time of the first dose. The second dose should be given 1 to 2 months after the first dose and the third dose 6 months after the first dose. The minimum interval between the first and second doses of vaccine is 4 weeks. The minimum interval between the second and third doses of vaccine is 12 weeks. The minimum interval between the first and third doses is 5 calendar months. If the vaccination series is interrupted, the series does not need to be restarted.

Last reviewed: March 2, 2024

Administration of Dengvaxia to a person who has never been infected with DENV may result in an increased risk of hospitalization and severe dengue illness if they are infected with natural (wild type) DENV for the first time after vaccination.

Multiple complex mechanisms likely contribute to increased disease severity during a second DENV infection. The published ACIP recommendation provides a detailed description of these mechanisms at www.cdc.gov/mmwr/volumes/70/rr/pdfs/rr7006a1-H.pdf. In addition, CDC has developed simple illustrations and descriptions to explain this phenomenon at https://www.cdc.gov/dengue/hcp/vaccine/eligibility.html.

In a person who has never been infected with DENV, vaccination with Dengvaxia may “stand in” (immunologically) for the first natural infection, resulting in an increased risk of severe dengue in response to the first natural infection because the immune system responds as if that infection were the “second” infection.

Last reviewed: February 16, 2022

People should avoid contact with any person who is severely immunosuppressed for at least 7 days after receiving FluMist (LAIV). There are no restrictions on being in contact with any other patients.

Last reviewed: August 11, 2024

The nirsevimab (Beyfortus, Sanofi) clinical trials demonstrated effective protection lasted at least 5 months (150 days) in preventing severe RSV disease (disease requiring medical attention, hospitalization or ICU admission). Protection may persist longer than 5 months, but this was the period of time studied in the trials.

Last reviewed: August 25, 2024

Clinical trial results for the original monovalent Pfizer-BioNTech COVID-19 Vaccine (administered as a two-dose primary series) demonstrated that among vaccine recipients age 12–15 years, side effects during the 7 days after vaccination were commonly reported (90.9% of vaccine recipients reported a local reaction and 90.7% reported a systemic reaction). Most reactions were mild to moderate. Pain at the injection site was the most common local reaction. One in 10 reported a side effect that interfered with daily activities. Side effects usually resolved after 1–2 days. Systemic side effects (e.g., fever, fatigue, headache, muscle pain) were more commonly reported after the second dose than after the first dose. No specific safety concerns were identified among adolescent vaccine recipients.

The safety and side effects of the 2024–2025 formula approved in August 2024 are expected to be consistent with the previous formulations of the product.

Last reviewed: August 31, 2024

The patient may be given one dose of PCV20 or PCV21. CDC estimates that PCV20 targets serotypes that cause approximately 54% of invasive pneumococcal disease (IPD) in people age 65 years and older in the United States and that PCV21 targets serotypes that cause approximately 85% of IPD cases in that U.S. age group. In some parts of the Western United States, pneumococcal serotype 4 is known to be responsible for more than 30% of IPD cases and state or local public health officials may advise healthcare providers that a product that covers serotype 4 (PCV20) may provide broader coverage than national estimates suggest. CDC does not recommend additional doses of PPSV23.

Last reviewed: November 13, 2024

Recommendations to separate MenACWY and PCV under certain circumstances only applied to MenACWY-D (Menactra, Sanofi), which is no longer available in the United States. So, you may administer any available and recommended MenACWY and PCV vaccines at the same time. A 10-year-old with persistent complement component deficiency also should receive a 3-dose series (the same product for all doses) of MenB vaccine.

As long as the child remains at high risk of meningococcal disease due to complement inhibitor use, booster doses of both MenACWY and MenB are recommended. A MenACWY booster dose should be given every 5 years and a MenB booster dose should be given one year after the completion of the primary series, followed by a booster dose every 2–3 years thereafter. If using MenB-FHbp (Trumenba, Pfizer), you have the option to use MenABCWY (Penbraya, Pfizer) when both MenACWY and MenB vaccinations are due at the same visit, as long as doses of Penbraya are separated by at least 6 months.

Because patients treated with complement inhibitors can develop invasive meningococcal disease despite vaccination, clinicians using Soliris, Ultomiris, Enjaymo, or other complement inhibitors also may consider antimicrobial prophylaxis for the duration of complement inhibitor therapy.

Last reviewed: November 15, 2024

Asthma is a precaution, not a contraindication, for FluMist (LAIV) in people 5 years of age and older. FluMist is contraindicated for children 2 through 4 years old who have had a diagnosis of asthma or whose parents or caregivers report that a health care provider has told them during the preceding 12 months that their child had wheezing or asthma or whose medical record indicates a wheezing episode has occurred during the preceding 12 months.

Last reviewed: August 11, 2024

An antiviral drug active against influenza virus may reduce the effectiveness of FluMist by interfering with the vaccine viruses’ ability to replicate in the upper airway in order to produce protective immunity. To prevent interference, ACIP has recommended different intervals between the last dose of an antiviral medication and FluMist administration, based upon the half-life of the antiviral medication. The recommendations are as follows:

  • Oseltamivir or zanamivir: wait at least 48 hours after the last dose before administering FluMist
  • Peramivir: wait at least 5 days before administering FluMist
  • Baloxavir: wait at least 17 days before administering FluMist

If any influenza antiviral medication must be given within 14 days after FluMist administration, the patient should be revaccinated without delay with any age-appropriate injectable influenza vaccine. Inactivated influenza vaccines (IIVs) and recombinant influenza vaccine (RIV) may be administered at any time relative to antiviral medication.

Last reviewed: August 11, 2024

A half dose of FluMist (or any other vaccine) is a non-standard dose and generally should not be counted. If you were unable to give the second half of the vaccine on the same day, you will have to provide another full dose of influenza vaccine at another time. If you want to give FluMist again, you should wait four weeks because it is a live vaccine. Alternatively, you can give an injectable influenza vaccine any time after this partial dose.

Last reviewed: August 11, 2024

ACIP recommends annual influenza vaccination for all children age 6 months and older who do not have a contraindication to the vaccine.

Last reviewed: August 11, 2024

People who have neither experienced primary varicella infection (chickenpox), nor received live-attenuated varicella vaccine (vaccine strain VZV, contained in Varivax, ProQuad, and Zostavax, all by Merck) are not at risk for shingles. More than 99% of Americans born before 1980 have had chickenpox, even if they don’t remember it, so additional screening is not recommended for immunocompetent people born before 1980 who are due for routine shingles vaccination. Children and adolescents who have received live-attenuated varicella vaccines (Varivax or ProQuad) are at risk for shingles, although they are at lower risk for shingles than are those who experienced chickenpox.

Shingrix (RZV) is not indicated and has not been studied for the prevention of chickenpox. Receipt of Shingrix is not considered proof of varicella immunity, and Shingrix cannot be considered as either of the two doses of the varicella vaccine series. In addition, there are limited data on the use of Shingrix in people without a history of chickenpox, with or without a history of varicella vaccination.

The consequences of primary varicella infection in immunocompromised adults can be severe. For adults who are or will be immunocompromised, evidence of immunity to varicella (confirming need for RZV) includes:

  • Documentation of two doses of varicella vaccine, or
  • Laboratory evidence of immunity or laboratory confirmation of disease, or
  • Diagnosis or verification of a history of varicella or herpes zoster by a healthcare provider.

Protection from primary varicella infection (chickenpox) is a priority for an adult who is or will be immunocompromised with no evidence of immunity to chickenpox. Refer to the ACIP varicella vaccine recommendations for further guidance, including post-exposure prophylaxis guidance for immunocompromised adults: www.cdc.gov/mmwr/preview/mmwrhtml/rr5604a1.htm.

Last reviewed: March 9, 2022

Yes. ACIP recommends the 2-dose schedule for people starting the HPV vaccination series before the 15th birthday, as long as they are immunocompetent.

Last reviewed: March 2, 2024

Yes; people who are identified as being at risk for HBV infection during pregnancy should be vaccinated. They also should be counseled concerning other methods to prevent HBV infection. Providers should administer an age-appropriate 3-dose series of Twinrix, Engerix-B or Recombivax HB.

Until safety data are available for Heplisav-B or PreHevbrio administration during pregnancy, ACIP does not recommend the use of either of these products to vaccinate during pregnancy. Pregnancy testing prior to administration of these products is not recommended.

Last reviewed: July 21, 2023

The dose should be repeated. If the error was detected on the same clinic day, you can repeat the dose that day. If the error is detected more than one day later and if the expired dose is a live virus vaccine, you must wait at least 28 days after the previous (expired) dose was given before repeating it. If the expired dose is not a live vaccine, the dose should be repeated as soon as possible. An exception to this is for recombinant zoster vaccine (Shingrix, GSK); the repeat dose should be given 4 weeks after the invalid dose, to reduce the risk of side effects caused by the adjuvant used to enhance the effectiveness of this vaccine. If you prefer, you can perform serologic testing to check for immunity for certain vaccinations (e.g., measles, rubella, hepatitis A, diphtheria, varicella, and tetanus).

Last reviewed: July 26, 2023

The most frequently reported side effects among vaccine recipients in the clinical trials were headache (40%), injection site pain (32%), malaise (25%), fatigue (25%), and muscle aches (29%).

As with any vaccine, healthcare providers should report any clinically significant adverse event to the Vaccine Adverse Events Reporting System (VAERS) at www.vaers.hhs.gov. even if a causal relation to vaccination is unknown or not certain.

Last reviewed: February 16, 2022

Minimum intervals for Twinrix are 4 weeks between dose #1 and dose #2, and 5 months between dose #2 and dose #3.

Last reviewed: July 15, 2023

Yes. Household contacts and other close contacts of people who are immunocompromised (due to a disease, or treatment for a disease) should receive all routinely recommended vaccines, with the exception of smallpox vaccine. The live MMR, varicella, and rotavirus vaccines should be administered to susceptible household contacts and other close contacts of immunocompromised patients when indicated. MMR vaccine viruses are not transmitted to contacts, and transmission of vaccine strain varicella-zoster virus is rare. No specific precautions are needed unless the varicella vaccine recipient has a rash after vaccination, in which case direct contact with susceptible immunocompromised household contacts should be avoided until the rash resolves. All members of the household should wash their hands after changing the diaper of an infant who received rotavirus vaccine. This minimizes rotavirus transmission, as shedding may occur up to one month after the last dose.

Household and other close contacts of immunocompromised persons should receive annual influenza vaccination. Introduction of low levels of vaccine viruses into the environment likely is unavoidable when administering quadrivalent live attenuated influenza vaccine (LAIV4; Flumist, Medimmune). LAIV4 vaccine viruses are cold-adapted so they can replicate in the nose and generate an immune response without entering the lungs (that is, they are temperature sensitive and replicate poorly at core body temperatures). No instances have been reported of illness caused by attenuated vaccine virus infections among healthcare providers or immunocompromised patients. LAIV may be administered to healthy nonpregnant household and other close contacts of immunocompromised people unless the immunocompromised person is hospitalized in a protective environment, typically defined as a specialized patient-care area with a positive airflow relative to the corridor, high-efficiency particulate air filtration, and frequent air changes. A person who is administered LAIV4 should not have contact with an immunocompromised person in this type of protective environment for 7 days after administration.

Last reviewed: August 29, 2022

No. In March 2014, FDA lowered the age indication for Adacel brand Tdap vaccine (Sanofi) from age 11 years to age 10 years. Both Tdap products, Adacel and Boostrix (GSK), now have the same lower age indication.

Last reviewed: March 31, 2022

While a complete series of HepA is recommended for long-term protection, even a single dose of HepA vaccine has been demonstrated to provide protection against hepatitis A for more than 10 years and can prevent or control outbreaks of hepatitis A. People who are experiencing homelessness may have difficulty protecting themselves from exposure to HAV in other ways because of their living conditions. They should be vaccinated when possible and provided a record of immunization. Reporting the HepA vaccination to a state immunization information system also can facilitate immunization assessment at future healthcare encounters.

Last reviewed: June 25, 2023

Yes. A 5/8″ needle is recommended for subcutaneous injections for people of all sizes. See Immunize.org’s clinical resource “How to Administer Intramuscular and Subcutaneous Vaccine Injections” at www.immunize.org/catg.d/p2020.pdf.

Last reviewed: June 19, 2023

In general, a vaccine should not be prepared until the provider is ready to administer it to a patient. This is because once the syringe cap is removed or a needle is attached, the sterile seal is broken. However, if a sterile seal has been broken, staff should be sure to maintain the syringe at the appropriate temperature and either use it or discard it at the end of the clinic day. This issue is addressed in the CDC Storage and Handling Toolkit, available at www.cdc.gov/vaccines/hcp/admin/storage/toolkit/storage-handling-toolkit.pdf, page 20.

Last reviewed: December 28, 2022

Varicella postvaccination serologic testing is not recommended; however, if a person tests positive for varicella antibody 28 days or more after vaccination, the Advisory Committee on Immunization Practices (ACIP) considers the person to be immune. Studies have shown that a second dose boosts antibody titers and indicators of cell-mediated immunity significantly above the levels produced by a single dose. A second dose may be required to comply with school entry or institutional immunization requirements, regardless of serologic test results. You can access the ACIP varicella vaccine recommendations, which include evidence of immunity (page 16) at www.cdc.gov/mmwr/pdf/rr/rr5604.pdf.

Last reviewed: September 5, 2023

Yes, it is. Infants and toddlers eligible for the VFC program may receive nirsevimab (Beyfortus, Sanofi) when  recommended in the same way and in the same facilities where they receive VFC vaccines. Providers who participate in VFC should follow all VFC requirements for ordering, storage, and administration established by their state immunization program.

Last reviewed: August 25, 2024

Yes. The 2024–2025 formula Novavax vaccine is an option for any person age 12 years or older who is unvaccinated or was previously vaccinated with any COVID-19 vaccine and is due for a 2024–2025 updated vaccination. Any person age 12 years or older who has never had a dose of any COVID-19 vaccine should receive two doses of Novavax vaccine, administered 3 to 8 weeks apart, as a primary series.

Adults age 65 years or older who are not immunocompromised and who did not require a 2-dose primary series with the current 2024–2025 Formula are NOT recommended to receive any additional doses of the current 2024–2025 Formula at this time.

Novavax recipients with moderate to severe immunocompromise being vaccinated for the first time may receive a third dose at least 2 months following the second dose in their primary series and may receive subsequent additional doses at the discretion of their healthcare provider, in consideration of their individual circumstances.

Additional details from FDA are available: www.fda.gov/vaccines-blood-biologics/coronavirus-covid-19-cber-regulated-biologics/novavax-covid-19-vaccine-adjuvanted.

Last reviewed: August 31, 2024

No. All adults age 50 years and older without a prior PCV vaccination are now routinely recommended to receive PCV20 or PCV21 alone or a 2-dose series of PCV15 followed by PPSV23 one year later. People in this age group with an immunocompromising condition, cochlear implant, or cerebrospinal fluid leak who are given PCV15 may receive PPSV23 as little as 8 weeks later. PCV13 is no longer recommended for adults; however, CDC states that in rare situations where no PCV15, PCV20, or PCV21 is available and a patient is otherwise unlikely to be vaccinated at all, an available dose of PCV13 may be used.

Last reviewed: November 13, 2024

Yes. Studies from the United States, South Africa, and the United Kingdom have shown that people with HIV infection have a risk of invasive meningococcal disease that is 11–24 times higher than the general population. In the United States, this excess risk is specifically for serogroups C, W, and Y. ACIP recommends routine MenACWY vaccination of all HIV-infected people 2 months of age and older. Children younger than age 2 years should be vaccinated using a multidose schedule based upon age (see the Immunize.org document “Meningococcal ACWY Vaccine Recommendations by Age and Risk Factor,” available at www.immunize.org/catg.d/p2018.pdf for details).

People age 2 years and older with HIV infection who have not been previously vaccinated should receive a 2-dose primary series of MenACWY (doses separated by at least 8 weeks). People with HIV infection who have previously received one dose of MenACWY should receive a second dose at the earliest opportunity (at least 8 weeks after the previous dose) and then receive booster doses at the appropriate intervals. ACIP does not recommend routine meningococcal serogroup B vaccination of people with HIV infection.

Last reviewed: November 15, 2024


3:18

View All Video Questions

Last reviewed: May 23, 2023

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

There are five injectable inactivated influenza vaccine (IIV) options for children. Four egg-based IIVs and one cell culture-based (ccIIV), all given as intramuscular (IM) injections, are approved for children age 6 months and older:

  • Afluria (CSL Seqirus): 0.25 mL/dose for age 6 through 35 months; 0.5 mL/dose for age 3 years and older
  • Fluarix (GSK): 0.5 mL/dose for age 6 months and older
  • FluLaval (GSK): 0.5 mL/dose for age 6 months and older
  • Fluzone (Sanofi): 0.25 mL or 0.5 mL per dose for age 6 through 35 months; 0.5 mL/dose age 3 years and older
  • Flucelvax (ccIIV, CSL Seqirus) cell-based (no egg antigen): 0.5 mL/dose for age 6 months and older

One egg-based live attenuated nasal spray vaccine, FluMist (LAIV, AstraZeneca), is an option for healthy, non-pregnant people age 2 years and older: 0.2 mL (intranasal, 0.1 mL in each nostril).

Last reviewed: August 11, 2024

There are insufficient data available to inform assessment of Heplisav-B or PreHevbrio vaccine-associated risks during pregnancy.

Dynavax has established a Heplisav-B Vaccination in Pregnancy Registry in order to understand the effect (if any) of Heplisav-B vaccination during pregnancy. Individuals who receive Heplisav-B within 28 days before pregnancy or at any time during pregnancy are encouraged to participate in the registry by calling 1-844-443-7734 (toll-free).

VBI has established a registry that monitors pregnancy outcomes in mothers exposed to PreHevbrio during pregnancy. Individuals who receive PreHevbrio during pregnancy are encouraged to contact 1-888-421-8808 (toll-free).

Last reviewed: July 21, 2023

No, do not restart the series. You should continue where the patient left off and complete the series.

Last reviewed: March 2, 2024

An adult who has documentation of one dose of varicella vaccine is potentially at risk for chickenpox (from exposure to a person with chickenpox) AND herpes zoster (either from a possible previous unrecognized case of chickenpox or from the vaccine strain of the virus).

CDC subject matter experts advise that clinical management of a person with no proof of a past primary varicella infection and a history of only one varicella vaccination who is or will be immunocompromised depends upon the degree of immunocompromise of the patient:

  • If varicella vaccine is not already contraindicated due to significant immunocompromise, give the second varicella vaccine dose. Depending on the patient’s immunocompromising condition or therapy, the clinician may then consider initiating the Shingrix series at least 8 weeks after the second varicella vaccine dose to reduce the risk of herpes zoster.
  • If the patient already has significant immunocompromise and the second varicella vaccine dose is contraindicated, the clinician should:
    • Consider the patient’s herpes zoster risk (based on their immunocompromising condition or therapy). On a case-by-case basis and if the clinician determines it is indicated, administer the Shingrix series to reduce the risk of herpes zoster.
    • Be prepared to administer varicella immune globulin (VariZIG, Saol Therapeutics) in the event that the patient has a recognized exposure to a person with chickenpox, regardless of whether or not the patient received RZV.

For more information, see www.cdc.gov/shingles/vaccination/immunocompromised-adults.html.

Last reviewed: March 9, 2022

Test pregnant people who lack either (1) documentation of receipt of 2 doses of varicella vaccine or (2) healthcare provider diagnosis or verification of varicella or herpes zoster disease. Those who are not immune should begin the 2-dose vaccination series immediately postpartum.

Last reviewed: May 16, 2023

No. A number of studies have shown that HCP are not at significantly increased risk of HAV infection because of their occupation. However, if HCPs are going to work (or vacation) in a country with a high or intermediate endemic rate of HAV infection, they are at risk of HAV infection and should be vaccinated. The only occupational indications for routine HepA vaccination are work with non-human primates or live HAV in a laboratory setting.

Last reviewed: June 25, 2023

In clinical trials and in postlicensure safety surveillance, the most common local adverse events within 7 days of receiving MenB were injection site pain, swelling or redness and the most common systemic symptoms were headache, fatigue and body aches. In general, these types of self-limited reactions are reported more frequently than with MenACWY vaccination.

Last reviewed: March 24, 2024

There are various requirements for the use of vaccines after reconstitution. Some manufacturers’ package inserts require that the vaccine be used or discarded in varying time frames ranging from 24 hours after reconstitution to “immediately” after reconstitution. While the specific timeframes are simple to interpret, there can be some confusion as to what the requirement of “immediately” actually means.

CDC considers “immediately” to be the reasonable time it takes to prepare and transport the vaccine to the patient to be administered. This would include any limited documentation that may be related to this process. It is up to the judgment of a provider to determine if a vaccine has not been used in the appropriate time. Some manufacturers have indicated to providers that “immediately” can be up to 30 minutes. The definition of “immediately” varies from manufacturer to manufacturer. Some do not have the data to put forth a general timeframe as to what “immediately” means. CDC recommends that the provider contact the manufacturer if any question arises about whether or not a vaccine dose has been used in the appropriate timeframe.

Last reviewed: July 26, 2023

Syncope (fainting) can occur before or after vaccination because of a vasovagal response to needles. Children should be seated or lying down during vaccination. Consider observing patients (with the patient seated or lying) for 15 minutes after vaccination to decrease the risk for injury should the patient faint. If syncope develops, the patient should be observed until the symptoms resolve.

Last reviewed: February 16, 2022

Yes. This was a vaccine administration error since Twinrix, a combination hepatitis A/hepatitis B vaccine, is not licensed for people younger than 18. However, the hepatitis A and hepatitis B components can be counted as valid doses. The third dose of the Twinrix series should be given at least five months after the second dose.

Last reviewed: July 15, 2023

Antibody titers to vaccine-preventable diseases decline during the 1-4 years after HCT, if the recipient is not revaccinated. HCT recipients are at increased risk for certain vaccine-preventable diseases, including those caused by encapsulated bacteria. In short, all HCT recipients should begin revaccination with inactivated vaccines 6 months after HCT. Three doses of pneumococcal conjugate vaccine (PCV) should be given 6 months following transplant followed by a dose of pneumococcal polysaccharide vaccine (PPSV) at least 8 weeks later. HCT recipients should receive 3 doses of Hib vaccine starting 6 to 12 months after successful transplant, regardless of vaccination history; doses should be administered at least 4 weeks apart. Immunocompetent people should receive MMR vaccine 24 months after transplant. For a complete discussion of the indications and schedule of vaccination, refer to the sub-section on recipients of HCT in the Altered Immunocompetence section of ACIP’s “General Best Practices Guidelines for Immunization” available at www.cdc.gov/vaccines/hcp/acip-recs/general-recs/immunocompetence.html.

Last reviewed: August 29, 2022

Tdap vaccination for adolescents is recommended at age 11–12 years. A 10-year-old who is already up to date on diphtheria/tetanus/pertussis vaccines and gets a Tdap vaccine for any reason does not need to receive another Tdap at age 11–12 years.

Last reviewed: March 31, 2022

Removing the protective cap increases the likelihood the septum or stopper could be punctured. The puncture may not be visible. It is important to ensure that the rubber seal on single-dose vials is not punctured because single-dose vials do not contain a preservative. Once the protective cap has been removed, the vaccine should be discarded at the end of the workday because it may not be possible to determine if the rubber seal has been punctured. For additional details, see CDC’s Vaccine Storage & Handling Toolkit at www.cdc.gov/vaccines/hcp/admin/storage/toolkit/storage-handling-toolkit.pdf.

Last reviewed: December 28, 2022

Children age 6 months through 8 years should receive a second influenza vaccine dose 4 weeks or more after the first dose if they meet one of the following three criteria: 1) they are receiving influenza vaccine for the first time, or 2) they have not received a total of at least two doses of any seasonal influenza vaccine before July 1 of the current year, or 3) their vaccination history is unknown. The two previous doses need not have been received during the same season or consecutive seasons.

A child who is 8 years old and is recommended to receive two doses during the current season and turns 9 during the current season before receiving dose 2, should still receive dose 2.

Immunize.org’s handout titled “Guide for Determining the Number of Doses of Influenza Vaccine to Give to Children Age 6 Months Through 8 Years” provides additional guidance on this issue; it is available at www.immunize.org/catg.d/p3093.pdf.

Last reviewed: August 11, 2024

ACIP recommends one dose of nirsevimab (Beyfortus, Sanofi) preventive antibody for all infants less than 8 months and 0 days of age who are born during or are entering their first RSV season.

ACIP also recommends one dose of nirsevimab for specific groups of infants and children age 8 through 19 months who are entering their second RSV season and at increased risk for severe RSV disease. These include the following:

Children 8 through 19 months at high risk and ineligible for palivizumab:

  • American Indian or Alaska Native children entering their second RSV season. This is especially important for those who are in remote regions or in communities known to have increased rates of severe RSV disease in children.

Children age 8 through 19 months at high risk and eligible for palivizumab (Synagis, AstraZeneca):

  • Children with chronic lung disease of prematurity who require medical support during the six months before the start of their second RSV season
  • Children who are severely immunocompromised
  • Children with evidence of severe cystic fibrosis (previous hospitalization for pulmonary exacerbation in the first year of life or abnormalities on chest imaging that persist when stable) or that have weight-for-length that is less than the 10th percentile

If nirsevimab is given to a child eligible for palivizumab, do not give palivizumab. If nirsevimab is unavailable, CDC recommends that palivizumab (a short-acting RSV monoclonal antibody) should be administered per AAP recommendations (see https://doi.org/10.1542/peds.2023-061803). Because palivizumab is effective for 30 days, if nirsevimab becomes available during the RSV season, aim to administer nirsevimab at the end of the 30-day period following the dose of palivizumab. Do not give palivizumab during the season after administering nirsevimab. In February 2024, AAP published updated guidance on prevention of RSV disease and the use of palivizumab when nirsevimab is unavailable: https://publications.aap.org/redbook/resources/25379/AAP-Recommendations-for-the-Prevention-of-RSV.

The full ACIP recommendation is available at www.cdc.gov/mmwr/volumes/72/wr/pdfs/mm7234a4-H.pdf.

Find further clinical considerations and information at CDC’s web page for healthcare providers on RSV immunization for infants and young children: www.cdc.gov/vaccines/vpd/rsv/hcp/child.html.

Last reviewed: August 25, 2024

Yes. Evidence continues to demonstrate that COVID-19 vaccination is safe and effective during any stage of pregnancy; the benefits of vaccination clearly outweigh any known or potential risks of COVID-19 vaccination during pregnancy. The currently licensed or authorized COVID-19 vaccines are non-replicating vaccines and cannot cause infection in either the pregnant person or the fetus. No evidence exists of risk to the fetus from vaccinating pregnant people with non-replicating vaccines in general.

Data from the Vaccine Adverse Events Reporting System (VAERS), the V-safe surveillance system, and the V-safe pregnancy registry have not signaled any safety concerns for pregnant people who were vaccinated or their infants.

All people who are pregnant are recommended to receive a 2024–2025 Formula COVID-19 vaccine, as licensed or authorized by FDA, if they have not already received one.

Last reviewed: August 31, 2024

No. All adults for whom pneumococcal vaccination is recommended due to age (50 or older) or an underlying condition (age 19 through 49) are now recommended to receive a pneumococcal conjugate vaccine. When PCV20 or PCV21 is given, no further pneumococcal vaccination is recommended. If PCV15 is given to an adult, PPSV23 is recommended one year later (minimum interval of 8 weeks). Prior recipients of PPSV23 alone may now receive PCV15, PCV20, or PCV21 at least 1 year after the dose of PPSV23.

Last reviewed: November 13, 2024

This page was updated on .

Our Affiliated Sites

For the Public: VaccineInformation.org
For Coalitions: ImmunizationCoalitions.org
65+ Flu Defense
Protect vulnerable, older adult patients from influenza.
Give2MenACWY.org
Improve protection from meningococcal serogroups ACWY.
Mass Vaccination Resources
Access guidance documents, toolkits, and helpful resources.
NAIIS
Home of the National Adult and Influenza Immunization Summit.