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 (1372)

CDC has included in the Vaccine Storage and Handling Toolkit an addendum that contains additional details concerning special considerations for COVID-19 and mpox vaccines. This is available at www.cdc.gov/vaccines/hcp/admin/storage/toolkit/storage-handling-toolkit.pdf.

Last reviewed: July 26, 2023

Eculizumab (Soliris) and related long-acting compounds, such as ravulizumab (Ultomiris) and sutimlimab (Enjaymo), inhibit the terminal complement pathway. People with persistent complement component deficiency due to an immune system disorder or use of a complement inhibitor are at increased risk for meningococcal disease even if fully vaccinated. This patient should be given a 2-dose primary series of MenACWY vaccine (2 doses separated by at least 8 weeks) and a 3-dose series of MenB vaccine (0, 1-2 months, and 6 months). The patient should receive regular booster doses of MenACWY and MenB as long as he remains at risk: a booster dose of MenACWY every 5 years and a booster dose of MenB one year after completion of the primary series, followed by a booster dose of MenB every 2–3 years thereafter. Because MenB products are not interchangeable, all MenB doses should contain the same type of MenB vaccine (either MenB-4C, which is in Bexsero [GSK], or MenB-FHbp, which is in Trumenba and Penbraya [Pfizer]). If the brand of the primary series is not known or not available, CDC recommends restarting the primary series with the available product.

Penbraya (MenABCWY, Pfizer) contains MenB-Fhbp (Trumenba, Pfizer) and is given as two doses, 6 months apart, when vaccination against all 5 serogroups is needed. For people age 10 years or older at increased risk of meningococcal disease, like this patient, Penbraya may be used for MenACWY and MenB (Trumenba) doses (including booster doses) if both vaccines would be given on the same clinic day and at least 6 months have elapsed since most recent Penbraya dose.

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

Last reviewed: November 15, 2024

Because more than one type or subtype of influenza virus can circulate in any given influenza season, providers should offer influenza vaccination to unvaccinated people throughout the influenza season, including people who may have had an influenza illness already in the season.

Last reviewed: August 11, 2024

Varicella vaccine is most effective in preventing chickenpox or reducing the severity of the disease if used within 72 hours (3 days), and may still be helpful up to 5 days after exposure. However, not every exposure to varicella leads to infection, so for future immunity, varicella vaccine should be given to a person age 12 months or older who does not have a contraindication to vaccination, even if more than 5 days have passed since an exposure.

Last reviewed: May 16, 2023

Infliximab is an IgG monoclonal antibody that neutralizes the biological activity of tumor necrosis factor-alpha. Like other IgG antibodies infliximab crosses the placenta. Infliximab has been detected in the blood of infants up to 6 months following birth. Consequently, these infants may be at increased risk of serious infection.

Neither ACIP nor CDC provides specific guidance on this issue because there are few data on safety or efficacy in children exposed to potentially immunosuppressive biologics during pregnancy. As noted above, practitioners should consider the potential risks and benefits of administering rotavirus vaccine to infants with known or suspected altered immunocompetence. Consultation with an immunologist or infectious diseases specialist is advised.

The manufacturer recommends that live vaccines (rotavirus and BCG) be deferred for at least six months after birth for infants whose mothers received infliximab during pregnancy. Hence, if a practitioner follows the manufacturer’s recommendation the child would not be eligible to receive rotavirus vaccine because according to ACIP guidelines the rotavirus vaccine series should not to be started after age 15 weeks 0 days.

Inactivated vaccines should be given on schedule.

Last reviewed: June 7, 2023

Hib meningitis incidence historically peaked at a younger age (4–6 months) among AI/AN infants than among other U.S. infant populations (6–7 months). Vaccination with a primary series of PedvaxHib (PRP-OMP, Merck) is preferred for AI/AN infants because this vaccine can produce a protective antibody response after the first dose.

At the current time, it is unknown whether Vaxelis (DTaP-IPV-Hib-HepB), which contains a smaller quantity of PRP-OMP than PedvaxHib, produces a similar protective antibody response after the first dose. Therefore, Vaxelis is not preferred for AI/AN infants at this time.

Last reviewed: July 31, 2022

ACIP recommends a 3-dose Dengvaxia vaccine schedule, with doses administered at 0, 6 months, and 12 months.

Last reviewed: January 17, 2025

No. ACIP does not recommend aspiration when administering vaccines because no data exist to justify the need for this practice. There are data that show that aspiration is more painful for the vaccine recipient. IM injections are not given in areas where large vessels are present. Given the size of the needle and the angle at which you inject the vaccine, it is difficult to cannulate a vessel without rupturing it and even more difficult to actually deliver the vaccine intravenously. We are aware of no reports of a vaccine being administered intravenously and causing harm in the absence of aspiration.

Last reviewed: December 28, 2022

Yes. Adults with a history of herpes zoster should receive Shingrix. If a person is experiencing an episode of zoster, vaccination should be delayed until the acute phase of the illness is over and symptoms abate.

Last reviewed: March 9, 2022

No. There is no federal requirement for signed consent for any dose of a vaccine licensed for use by the FDA. The federal requirement is to provide all adult patients or parents/legal representatives of minor children with the appropriate VIS for each dose of vaccine administered. Some clinics, agencies, and/or state immunization programs may have requirements for signatures. Contact information for your state health department is available at www.immunize.org/coordinators.

Last reviewed: June 6, 2023

Begin by asking a general question about whether the person has an allergy to any food, medication, or vaccine. If they report an allergy to gelatin or foods that contain gelatin, you could follow up by asking if they can eat Jell-O™ and gelatin-type products. Gelatin allergies are extremely rare. Only severe, life-threatening (anaphylactic) allergy is a contraindication to vaccination.

Last reviewed: August 29, 2022

Historically, AI/AN infants were more likely than other U.S.-born infants to develop Hib meningitis before being old enough to complete a primary series of Hib-containing vaccine. ACIP prefers that AI/AN infants be vaccinated with PedvaxHIB because it can stimulate protective levels of antibodies after the first dose.

Vaxelis contains the same Hib vaccine components as PedvaxHIB, but in smaller quantities. At the time ACIP approved Vaxelis, no data were available on the immune response to the Hib component of Vaxelis after the first dose, so ACIP did not make a preferential recommendation for Vaxelis in AI/AN infants. ACIP stated it would re-evaluate its decision if new information becomes available.

Last reviewed: July 15, 2023

Congratulations on your hard work! You would be surprised at the number of people who, just like you, do a careful job of recording temperatures, but then they fail to act on them when the temperatures go out of range. Always take immediate action when you notice an out-of-range temperature. You may need to move the vaccines temporarily to a more reliable storage unit and determine the source of the problem. It may be something quite fixable (e.g., excessive lint or dust on the coils), and you will be back in business after you determine that the temperature is back in range after a few hours.

Above all, don’t chart an out-of-range temperature and not act on it! Immunize.org has created temperature recording logs and a troubleshooting record to document unacceptable vaccine storage events. The CDC Storage and Handling Toolkit contains detailed guidance on the management of a temperature excursion. See pages 15–17 at www.cdc.gov/vaccines/hcp/admin/storage/toolkit/storage-handling-toolkit.pdf. Refer to the addendum to the toolkit for specific guidance on COVID-19 and mpox vaccines.

Last reviewed: July 26, 2023

There is no ACIP recommendation for additional doses of 9vHPV for people who started the series with 2vHPV or 4vHPV and completed the series with 9vHPV.

Last reviewed: March 2, 2024

As of 2024, there are two options for MenACWY vaccination. In 2020, MenQuadfi (Sanofi) was approved for use in all people ages 2 years and older. If MenQuadfi is not available and vaccination is needed, you may administer Menveo.

Last reviewed: November 15, 2024

PPSV23 is not effective in children less than 24 months of age. PPSV23 given to children younger than 2 years old should not be considered part of the pneumococcal vaccination series. PCV15 or PCV20 should be administered as soon as the error is discovered. Any time the wrong vaccine is given, the parent/patient should be notified. The facility staff should review their vaccination training and clinical procedures to prevent future vaccine administration errors.

Last reviewed: November 13, 2024

Recommendations to separate MenACWY and PCV only applied to MenACWY-D (Menactra, Sanofi), which is no longer available in the United States. You may administer PCV vaccines and MenQuadfi, Menveo, or Penbraya (if this MenABCWY is indicated) at the same time. A 10-year-old with persistent complement component deficiency also should be vaccinated against MenB with an appropriate 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.

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

Last reviewed: November 15, 2024

No. RSV vaccination during pregnancy is only recommended for pregnant people who have not previously received an RSV vaccine and who are at the recommended stage of pregnancy (32 weeks through 36 weeks 6 days’ gestation) during the recommended time of year (typically September through January). In regions with seasonal patterns of RSV that differ from the continental United States, such as Alaska, Hawaii, or subtropical parts of Florida, follow state or territorial public health guidance on timing, which may differ.

Last reviewed: August 25, 2024

In the 2013 revision of its MMR vaccine recommendations ACIP expanded the use of post-exposure IG prophylaxis for measles. Intramuscular IG (IGIM) should be administered to all infants younger than 12 months who have been exposed to measles. The dose of IGIM is 0.5 mL/kg of body weight; the maximum dose is 15 mL. Alternatively, MMR vaccine can be given instead of IGIM to infants age 6 through 11 months, if it can be given within 72 hours of exposure.

In addition to infants under the age of 12 months, immune globulin may be used as measles post-exposure prophylaxis for susceptible pregnant people or susceptible people who are severely immunocompromised. For details on the dosage and use of immune globulin, please refer to the measles control section in Chapter 7 of the CDC Manual for the Surveillance of Vaccine-Preventable Diseases:  https://www.cdc.gov/surv-manual/php/table-of-contents/index.html.

IG is not indicated for people who have received 1 dose of measles-containing vaccine at age 12 months or older unless they are severely immunocompromised. IG should not be used to control measles outbreaks. IG has not been shown to prevent mumps or rubella infection after exposure and is not recommended for that purpose.

Last reviewed: June 19, 2023

Novavax COVID-19 Vaccine, Adjuvanted contains the Omicron JN.1 subvariant SARS-CoV-2 spike protein and Matrix-M adjuvant. The saponin-based adjuvant is made from extracts of the bark of the Soapbark tree native to Chile. It is added to enhance the immune response of the vaccine recipient. The spike protein is produced in insect cells.

It is authorized for emergency use in people age 12 years or older as a two-dose primary series for previously unvaccinated individuals (whether or not they are immunocompromised), with the doses given at least 3 to 8 weeks apart. Previously unvaccinated people age 65 years and older and previously unvaccinated people age 12 years and older who have moderate or severe immunocompromise should receive an additional dose 6 months after dose 2 (minimum interval 2 months). People with moderate or severe immunocompromise may receive additional doses of COVID-19 vaccine (minimum interval 2 months) as determined by their healthcare team, their personal preference, and specific circumstances. 

Individuals age 12 years through 64 years who have had one or more doses of any previous authorized or approved COVID-19 vaccine formulation are recommended to receive only one dose of the current 2024–2025 Novavax formulation. People age 65 years and older and people age 12 years and older with moderate or severe immunocompromise who have received one or more doses of a previous season’s COVID-19 vaccine and receive a dose of the 2024–2025 Formula Novavax vaccine should receive an additional dose of any 2024–2025 COVID-19 vaccine 6 months (minimum interval 2 months) following the first dose. Those with moderate or severe immunocompromise may receive additional doses as determined by their healthcare team, their personal preference, and specific circumstances. 

Last reviewed: November 16, 2024

There are two different DTaP products currently used in the U.S. for the primary series for children ages 2 months through 6 years (Daptacel [Sanofi] and Infanrix [GSK]). ACIP has recommended that, whenever feasible, healthcare providers should use the same brand of DTaP vaccine for all doses in the vaccination series. If vaccination providers do not know or have available the type of DTaP vaccine previously administered to a child, any DTaP vaccine may be used to continue or complete the series. For vaccines in general, vaccination should not be deferred because the brand used for previous doses is not available or is unknown (see the ACIP’s General Best Practices Guidance for Immunization at www.cdc.gov/vaccines/hcp/imz-best-practices/timing-spacing-immunobiologics.html).

Last reviewed: March 31, 2022

The schedule for HepB vaccination depends on the brand in use. Heplisav-B is administered intramuscularly on a 2-dose schedule with doses separated by 1 month (4 weeks). Routine primary vaccination with PreHevbrio (no longer available), Engerix-B, Recombivax HB, or Twinrix consists of three intramuscular doses administered on a 0-, 1-, and 6-month schedule.

Alternative vaccination schedules for Engerix-B and Recombivax HB (for example, 0, 1, and 4 months or 0, 2, and 4 months) have been demonstrated to elicit dose-specific and final rates of seroprotection similar to those obtained on a 0-, 1-, and 6-month schedule. Increasing the interval between the first 2 doses has little effect on immunogenicity or the final antibody concentration. The third dose confers the maximum level of seroprotection and provides long-term protection.

Recombivax HB may be administered in a 2-dose schedule at 0 and 4–6 months for adolescents age 11 through 15 years using the adult formulation (1.0 mL). Pediarix (GSK) and Vaxelis (MCM) combination vaccines are administered at age 2, 4, and 6 months; they are not used for the birth dose. Twinrix may be administered on an accelerated 4-dose schedule at 0, 7, and 21–30 days, followed by a dose at 12 months.

HepB vaccination of adult (age 20 years and older) hemodialysis patients consists of high-dose (40 µg) Recombivax HB administered on a 0-, 1-, and 6-month schedule or high-dose (2 mL) Engerix-B administered on a 0-, 1-, 2-, and 6-month schedule. Heplisav-B has not been studied in patients on hemodialysis.

Last reviewed: January 17, 2025

In general, vaccination series should be completed with the same product. However, CDC guidance states that you may complete a hepatitis B vaccination series with any available, age-appropriate hepatitis B product if the brand of the previous dose is unknown or unavailable.

One hepatitis B vaccine (Heplisav-B, Dynavax) is recommended as a 2-dose series, with doses administered at least 4 weeks apart. All other hepatitis B vaccine product options for adults (Engerix-B, GSK; Recombivax HB, Merck; Twinrix [HepA-HepB], GSK; and the discontinued product, PreHevbrio, VBI) are routinely recommended on a 3-dose schedule: 0, 1-2 months, and 6 months; dose 2 may be given a minimum of 4 weeks after dose 1 and dose 3 may be given a minimum of 8 weeks after dose 2 and 16 weeks after dose 1. The table below does not address the accelerated, 4-dose Twinrix (combination HepA-HepB) schedule option (doses given on days 0, 7, 21, and 12 months), nor does it address completion of the hepatitis A component of Twinrix.

The table below displays the options and timing for hepatitis B vaccination with a mixed-product series. All mixed-product options require 3 doses because the only 2-dose option is two doses of Heplisav-B. PreHevbrio (VBI) is no longer available for use in the United States; however, it is listed in order to guide completion of series initiated with PreHevbrio.

Timing of completion of a routine adult hepatitis B vaccination schedule with a single product or mixed product series:

Dose 1 Dose 2
(at least 4 weeks after dose 1)		 Dose 3
(at least 8 weeks after dose 2 and 16 weeks after dose 1)
Routine, single product schedule H* H —
E, P, R, or T* Same product as dose 1 Same product as dose 2
If different products are used E, P, R, or T E, P, R, or T E, P, R, or T
H E, P, R, or T E, P, R, or T
E, P, R, or T H E, P, R, or T
E, P, R, or T E, P, R, or T H
H E, P, R, or T H
E, P, R, or T H H**

* H = Heplisav-B; E = Engerix-B; P = PreHevbrio [no longer available]; R = Recombivax HB; T = Twinrix
** If two doses of H are used to complete a series started with E, P, R, or T, the final dose may be administered 4 weeks after dose 2 (for a complete H series). A 3-dose series containing 2 doses of H administered at least 4 weeks apart is valid, irrespective of the interval from doses of E, P, R, or T.

Last reviewed: January 17, 2025

There is no waiting period in such a situation. Shingles is not caused by exposure to another person with shingles. Shingles is caused by the reactivation of varicella zoster virus (VZV) in people who have had a prior VZV infection or varicella vaccination. However, exposure to someone with shingles can possibly cause chickenpox in a person with no immunity to varicella zoster virus (VZV) from either vaccination or prior chickenpox infection.

Last reviewed: March 9, 2022

The only way to determine whether the rash is caused by wild-type varicella or vaccine virus is to try to isolate virus from the rash and send it to a laboratory that is capable of differentiating wild and vaccine-type virus. This is generally not practical. Given the history, the conservative approach is to assume she has an active case of chickenpox and act according to your infection control guidelines.

Last reviewed: May 16, 2023

If the DTaP brand used for previous doses is not known or not in stock, use whatever DTaP vaccine you have available for all subsequent doses.

Last reviewed: March 31, 2022

CDC currently has no plans to develop VISs for Pediarix, Twinrix, Kinrix, Quadracel, or Pentacel. When administering these combination vaccines, use the VISs for all component vaccines. For certain combination vaccines given to children, you can use the multi-vaccine VIS (which includes DTaP, Hib, HepB, polio, and PCV) and check the appropriate box(es), just as you would if you were administering the individual vaccines. If the multi-vaccine VIS is unavailable, you should use the individual vaccine VISs. A VIS was developed for MMRV (ProQuad, by Merck) because of its unique adverse reaction profile.

Last reviewed: June 6, 2023

No. You should not use it until you know more. If you find that a vaccine has been exposed to an inappropriate temperature, try to determine the reason for the temperature excursion, mark the vaccine “Do Not Use,” and contact the manufacturer or the state or local health department to determine if the vaccine may be used without concern that its effectiveness has been diminished.

Do not leave vaccines in a storage unit that does not maintain temperatures within the recommended range. If you are unable to stabilize the temperature in your unit within the required range, or temperatures in the unit are consistently at the extreme high or low end of the range, identify an alternative unit with appropriate temperatures and sufficient storage space until the primary unit can be repaired or replaced.

Last reviewed: July 26, 2023

Having an immunocompromised household contact is not usually a reason for delaying routine vaccination for others in the household. Rotavirus vaccine should be administered to susceptible household contacts and other close contacts of immunocompromised patients when indicated. All members of the household should wash their hands after changing the diaper of an infant. This minimizes rotavirus transmission from an infant who received rotavirus vaccine. Additional information on this topic can be found in the ACIP “General Best Practice Guidelines for Immunization”, available at www.cdc.gov/vaccines/hcp/imz-best-practices/altered-immunocompetence.html.

Last reviewed: June 7, 2023

All Hib-containing vaccines should be administered by the intramuscular route.

Last reviewed: July 31, 2022

The effectiveness of Novavax COVID-19 Vaccine against currently circulating variants of SARS-CoV-2 is not precisely known. Clinical trials of this vaccine were conducted against earlier variants no longer in circulation; however, the vaccine showed very good effectiveness against moderate to severe disease during clinical trials. Testing conducted on antibodies in the serum of Novavax vaccine recipients suggests that vaccination provides substantial protection against severe disease and death caused by currently circulating variants, consistent with other available COVID-19 vaccines.

Last reviewed: November 16, 2024

Although aspiration is not recommended, if you do aspirate and get a flash of blood, then the procedure is to withdraw the needle and start over. The syringe, needle, and contaminated dose of vaccine should be discarded in a sharps container, and a new syringe and needle should be used to draw up and administer another dose of vaccine. This is a waste of expensive vaccine that could be avoided by simply not aspirating.

Last reviewed: December 28, 2022

Fever after vaccination was more common, reported in almost half of infants, compared to about one-third of infants who received Pentacel (DTaP-IPV/Hib). However, the rates of fever-related medical visits or febrile seizures were similar in both groups.

Last reviewed: July 15, 2023

No. Vaccines available in the United States do not contain peanut products.

Last reviewed: August 29, 2022

The recommended interval is 6 calendar months between each dose, and the minimum interval is 5 calendar months between each dose. In accordance with CDC’s general best practice guidelines, a dose administered up to 4 days before the minimum interval may be counted as valid. If a dose is given too early, the recommendation is to repeat the dose at the minimum interval of 5 months.

Last reviewed: January 17, 2025

The Advisory Committee on Immunization Practices (ACIP) recommends routine HepA vaccination for the following groups:

  • All children at age 1 year (12–23 months)
  • All children and adolescents age 2 through 18 years who have not previously received HepA should be vaccinated (i.e., routine catch-up vaccination)
  • People living with HIV infection
  • Travelers age 12 months and older to areas of the world with intermediate or high hepatitis A virus (HAV) endemicity. Low endemicity regions include the United States, Canada, Western Europe, Japan, New Zealand, and Australia. For more information, see the CDC travel health website for current information about specific countries at https://wwwnc.cdc.gov/travel or the CDC Yellow Book. (wwwnc.cdc.gov/travel/yellowbook/2020/travel-related-infectious-diseases/hepatitis-a). When in doubt, vaccinate.
  • Infants age 6 through 11 months traveling outside the United States should receive 1 dose when protection against HAV infection is recommended. The travel dose does not count toward the routine HepA series which should be initiated at age 1 year with the appropriate dose and schedule. In these instances, the child will receive a total of 3 doses of HepA vaccine.
  • Men who have sex with men
  • Users of illegal drugs, injectable or noninjectable
  • People who are homeless or in unstable living arrangements, including shelters
  • Previously unvaccinated people who anticipate having close personal contact with an international adoptee from a country of high or intermediate endemicity during the first 60 days following the adoptee’s arrival in the U.S.
  • People who work with HAV-infected nonhuman primates or with HAV in a research laboratory setting
  • People with chronic liver disease (including but not limited to people with hepatitis B infection, hepatitis C infection, cirrhosis, fatty liver disease, alcoholic liver disease, autoimmune hepatitis, or an ALT or AST level persistently greater than twice the upper limit of normal)
  • People identified during pregnancy to be at risk for HAV infection due to presence of a specific risk factor for exposure or at risk for severe outcome from HAV infection (for example, those with chronic liver disease or with HIV infection).
  • During an outbreak, any unvaccinated person who is identified as at risk for HAV infection or at risk for severe disease from HAV
  • Any person who wishes to be immune to hepatitis A

HepA vaccination is not routinely recommended for healthcare personnel, food handlers, sewage workers, or day care providers because there is no evidence that their occupational risks of HAV exposure are significantly higher than the general population. However, any person who desires protection from HAV infection may be vaccinated.

For details about CDC recommendations for the prevention of hepatitis A, see the 2020 recommendations of the Advisory Committee on Immunization Practices (ACIP): www.cdc.gov/mmwr/volumes/69/rr/pdfs/rr6905a1-H.pdf.

Last reviewed: June 25, 2023

ACIP and CDC do not recommend revaccination with 9vHPV of people who have completed a recommended series of another HPV vaccine given at appropriate dosing intervals.

Last reviewed: March 2, 2024

Only the Menveo two-vial formulation requiring reconstitution (MenACWY-CRM) should be used for children age 2 through 23 months. MenQuadfi (MenACWY-TT) is approved for people age 24 months or older. The one-vial formulation of Menveo that does not require reconstitution is approved for children and adults age 10 through 55 years. Penbraya (MenABCWY), may be an option for people age 10 years or older when both MenACWY and MenB (Trumenba) vaccination is needed at the same visit. Unlike MenB vaccines, when more than one brand of MenACWY vaccine is age-appropriate, they are interchangeable.

Last reviewed: November 15, 2024

Protection from influenza vaccine wanes after vaccination (the amount of protection and the speed of waning varies by strain and by recipient age), but generally persists for at least 5–6 months.

Last reviewed: August 11, 2024

Yes. Pfizer’s RSV vaccine (Abrysvo) may be administered to a previously unvaccinated pregnant person from 32 weeks through 36 weeks and 6 days’ gestation. RSV vaccine should not be administered to someone at 37 weeks’ gestation or beyond.

RSV vaccine should be administered at least 2 weeks before delivery to allow time for the maternal immune system to create antibodies and transfer sufficient antibodies to the fetus for adequate protection after birth. If the gestational age is appropriate, but clinical judgment is that delivery is likely to occur within 2 weeks, it is reasonable to defer vaccination and plan to administer nirsevimab RSV preventive antibody (Beyfortus, Sanofi) to the infant after delivery. Infants born less than 14 days after maternal RSV vaccination are recommended to receive nirsevimab after birth to ensure adequate protection.

Last reviewed: August 25, 2024

Single antigen vaccine is no longer available in the U.S.; the student should get the combined MMR vaccine. If a college student or other person at increased risk of exposure cannot produce written documentation of either immunization or disease, and titers are negative, they should receive two doses of MMR.

Last reviewed: June 19, 2023

For all ages, when the HepB schedule is interrupted, the vaccine series does not need to be restarted. If the Heplisav-B series is interrupted, the second (final) dose should be given as soon as possible. For Engerix-B, Recombivax HB, and PreHevbrio (no longer available), if the series is interrupted after the first dose, the second dose should be administered as soon as possible, and the second and third doses should be separated by at least 8 weeks. If only the third dose has been delayed, it should be administered as soon as possible.

Last reviewed: January 17, 2025

ACIP recommends vaccination with Shingrix for adults age 19 years or older who are immunodeficient or immunosuppressed due to disease or therapy. Repeated shingles episodes are often associated with immunocompromise. If your patient’s recurrent shingles episodes are evaluated and clinically concluded to be the result of immunodeficiency or immunosuppression, he should be vaccinated with a two-dose series of Shingrix.

Last reviewed: March 9, 2022

No. Self-reported doses and history of vaccination provided by a parent or other caregiver are not considered to be valid. You should only accept a written, dated record as evidence of vaccination.

Last reviewed: June 19, 2023

There is currently no information on the effect of varicella vaccine on reactivity to a tuberculin skin test (TST). Until information is available, it is prudent to apply the same rules to varicella vaccine as are applied to MMR: a TST (i.e., PPD) may be applied before (preferably) or simultaneously with varicella vaccine. If vaccine has been given, delay the TST for at least 4 weeks.

Last reviewed: May 16, 2023

If Tdap was inadvertently administered to a child under age 7 years, it should not be counted as either the first, second, or third dose of DTaP. The dose should be repeated with DTaP. Continue vaccinating on schedule. If the dose of Tdap was administered for the fourth or fifth DTaP dose, the Tdap dose can be counted as valid. Please remind your staff to always check the vaccine vial at least 3 times before administering any vaccine.

Last reviewed: March 31, 2022

This is a complex question that requires case-by-case review. First, while you’re assessing the situation, return the vaccine to proper storage temperatures and mark it “Do Not Use.” Then, contact your state or local immunization program or the appropriate vaccine manufacturer(s) to discuss the potential usability of the vaccine. They will need to consider several variables related to vaccine storage conditions. For example, their guidance will be affected by the type and accuracy of the temperature monitoring device, whether the temperature probe was in a liquid or was reading the temperature of the air, the type of vaccine involved, the length of time of the excursion, etc.

In general, if it can be reliably determined that the vaccine in question was not stored below 32°F and the manufacturer’s stability data concurs, most immunization programs and vaccine manufacturers would not recommend wasting the vaccine or revaccinating recipients.

Last reviewed: July 26, 2023

In the RotaTeq clinical trials in the first week after any dose vaccine recipients had a small but statistically significant increased rate of diarrhea (18.1% in the RotaTeq group, 15.3% in the placebo group) and vomiting (11.6% in the RotaTeq group, 9.9% in the placebo group). During the 42-day period following any dose, statistically significantly greater rates of diarrhea, vomiting, otitis media, nasopharyngitis and bronchospasm occurred in RotaTeq recipients compared with placebo recipients.

In the Rotarix clinical trials, in the first week after vaccination, Grade 3 (i.e., those that prevented normal everyday activities) cough or runny nose occurred at a slightly but statistically higher rate in the Rotarix group (3.6 %) compared with placebo group (3.2%). During the 31-day period after vaccination, these unsolicited adverse events occurred at a statistically higher incidence among vaccine recipients: irritability (11.4% in Rotarix group, 8.7% in placebo group) and flatulence (2.2% in Rotarix group, 1.3% in placebo group).

In clinical trials of both vaccines the occurrence of intussusception was studied very carefully; see the separate question and answer on this topic.

Last reviewed: June 7, 2023

Yes. Allergy to bee venom is not a contraindication for any vaccine.

Last reviewed: August 29, 2022

Not necessarily. Providers do not need to discard their existing printed VIS stocks when nothing but the VIS format has been changed. CDC posts information on its website to alert healthcare providers when the older version of a VIS should not be used. This information is available on CDC’s web section titled “What’s New with VISs”, available at www.cdc.gov/vaccines/hcp/vis/what-is-new.html.

Last reviewed: June 6, 2023
  • [added] All children ages 2 through 18 years not previously vaccinated
  • [added] All people age 1 year or older living with HIV infection
  • [added] People identified to be at risk for HAV infection during pregnancy
  • [removed] People with clotting factor disorders
Last reviewed: June 25, 2023

Yes.

Last reviewed: March 2, 2024

CDC has developed a “one-stop” product-specific webpage for each COVID-19 vaccine with all of the important details that immunization providers need to know: www.cdc.gov/vaccines/covid-19/info-by-product/index.html.

Last reviewed: November 16, 2024

In general, no. Occupational Safety and Health Administration (OSHA) regulations do not require the wearing of gloves when administering vaccinations, unless the person administering the vaccine is likely to come into contact with potentially infectious body fluids or has an open lesion on their hand. If a healthcare worker chooses to wear gloves, he or she must change them between each patient encounter.

In 2020, in response to the COVID-19 pandemic, CDC temporarily recommended the use of gloves when administering oral and intranasal vaccines to patients in communities where SARS-CoV-2, the virus that causes COVID-19, is circulating. Gloves were recommended to prevent contact with the recipient’s potentially infectious mucous membranes or respiratory secretions. In the setting of widely available and effective COVID-19 vaccines and treatments, CDC resumed recommending standard pre-pandemic infection control practices during vaccination.

Last reviewed: December 28, 2022

Dengvaxia is administered as a 3-dose series, spaced 6 months apart (0, 6, and 12 months). Each dose is 0.5 mL in volume, administered subcutaneously. The vaccine comes in powder form (lyophilized) in single dose vials. Each lyophilized vaccine vial should be mixed with the supplied diluent, a vial of saline diluent (0.4% NaCl). To reconstitute Dengvaxia, withdraw 0.6 ml from the diluent vial and inject it into the lyophilized vaccine vial. Swirl the vial gently. After reconstitution, the suspension is colorless and may develop trace amounts of white to translucent particles.

After reconstitution, 0.5 mL of Dengvaxia should be withdrawn and immediately administered subcutaneously. If not used immediately, the reconstituted vaccine should be refrigerated at 36°F–46°F (2°C–8°C) and used within 30 minutes. Do not use the vaccine more than 30 minutes after reconstitution.

Dengvaxia is for subcutaneous use only. Dengvaxia should not be administered by intramuscular injection; however, if administered intramuscularly in error, the dose does not need to be repeated.

CDC has a web page dedicated to the storage and reconstitution of Dengvaxia: https://www.cdc.gov/dengue/hcp/vaccine/storage-handling.html.

Last reviewed: January 17, 2025

First, injectable influenza vaccines cannot cause influenza because they contain only parts of the virus. The live attenuated nasal spray vaccine is modified so that it cannot cause influenza because it cannot replicate at human body temperature. Fewer than 1% of vaccinated people might develop flu-like symptoms, such as mild fever and muscle aches, after vaccination. These vaccine side effects are not the same as having influenza, but people may confuse the side effects with illness.

Other reasons a person might have had influenza illness or an illness that they thought might be “the flu” after vaccination include:

  • Protective immunity doesn’t develop until 1–2 weeks after vaccination. Some people who get vaccinated after influenza viruses are already circulating may be infected with influenza before the vaccination can stimulate protective immunity.
  • For many people, “the flu” is any illness with fever, cold symptoms or gastrointestinal symptoms. If they get any viral illness, they may blame it on influenza vaccine or think they got “the flu” despite being vaccinated. Influenza vaccine only protects against specific influenza viruses, not all viruses.
  • Vaccinated people can get influenza illness despite vaccination. Influenza vaccination is our best available protection against influenza disease; however, vaccination reduces the risk of infection, it does not prevent all infections.

Vaccine effectiveness (VE) varies by age and by season, depending upon the circulating viruses. In most recent seasons, influenza vaccination has reduced the risk of illness by between roughly 40% and 60% in the vaccinated population (including all ages) during seasons when most circulating influenza viruses are well-matched to the vaccine. VE is generally lower for adults age 65 years and older. Influenza vaccination has also been shown to reduce influenza disease severity even if someone does get sick after vaccination, and vaccination reduces the risk of influenza hospitalization and deaths in children and adults. Influenza vaccination also reduces the risk of stroke and acute cardiac events, like heart attack and heart failure, among people with heart disease.

For more information on this topic, go to: www.cdc.gov/flu-vaccines-work/index.html.

Last reviewed: August 11, 2024

Many pregnant people will have a choice about whether to get Abrysvo during pregnancy or to give nirsevimab (Beyfortus, Sanofi) to their infant after birth. Those who are previously unvaccinated and between 32 and 36 weeks 6 days’ gestation between September and January, may be vaccinated with Abrysvo or have their infant receive nirsevimab soon after birth (preferably within the first week of life if born during a month when nirsevimab administration is recommended).

It is important to note that both Abrysvo RSV vaccine and nirsevimab products may not be available or an option for all people in all settings. In some facilities or circumstances, only one option might be available: those offered Abrysvo during pregnancy may not wish to defer that option unless they are confident that nirsevimab will be available for their infant. Conversely, if the pregnant person received RSV vaccine before the current pregnancy, only nirsevimab administered after birth is recommended for RSV prevention. All infants up to 8 months 0 days of age whose mothers were not vaccinated may be given nirsevimab when feasible, before or during their first RSV season.

Last reviewed: August 25, 2024

Selective IgA deficiency is a B-cell immunodeficiency, so additional pneumococcal vaccination beyond the routine age-based schedule is indicated for this 6-year-old with an immunocompromising condition. Because the child received a complete PCV13 series, the current recommendation is to administer a single dose of PCV20 or PPSV23 at least 8 weeks following the most recent PCV dose. If PCV20 is given, no further doses of pneumococcal vaccine are recommended. If PPSV23 is given now, then at least 5 years later give a dose of PCV20 or a second dose of PPSV23. See CDC’s recommendations at: www.cdc.gov/pneumococcal/hcp/vaccine-recommendations/risk-indications.html. 

Last reviewed: November 13, 2024

Either Trumenba (MenB-FHbp) or the Bexsero MenB vaccine brand (MenB-4C) may be used for people with HIV infection. People with HIV infection do not appear to be at higher risk for meningococcal serogroup B disease, and ACIP does not specify use of the 3-dose schedule for people with HIV. Booster doses of MenB are not recommended for people with HIV in the absence of another indication for MenB vaccination.

Penbraya (MenABCWY, Pfizer) is an option for people age 10 years and older only when both MenACWY and MenB (Trumenba) vaccines are due at the same visit and at least 6 months have elapsed since the most recent dose of Penbraya. An adolescent with HIV should receive a 2-dose primary MenACWY series (with the doses given 8 weeks apart), followed by MenACWY booster doses every 5 years. If this teen needs the MenACWY primary series vaccination and also chooses to receive Trumenba, Penbraya may only be used for one of the doses because dose 2 in the MenACWY primary series is due 8 weeks after dose 1 and the minimum interval between Penbraya doses is 6 months.

Last reviewed: November 15, 2024

For people who are age 2 years or older, a 2-dose series of MenACWY, spaced 8–12 weeks apart, is recommended if they have functional or anatomic asplenia, HIV infection, persistent complement component deficiency (an immune disorder including C3, C5–C9, properdin, factor H, and factor D deficiency), or if they take a complement inhibitor (for example, eculizumab [Soliris], ravulizumab [Ultomiris], or sutimlimab [Enjaymo]). People with these high-risk medical conditions also need booster doses of MenACWY.

Last reviewed: November 15, 2024

The minimum interval between the two doses of Heplisav-B is 4 weeks. For the 3-dose series vaccines, Engerix-B, PreHevbrio (no longer available), and Recombivax HB, the minimum interval between the first and second doses is 4 weeks. The final dose of vaccine must be administered at least 8 weeks after the second dose and should follow the first dose by at least 16 weeks. Vaccine doses administered 4 or fewer days before the minimum interval or age are considered valid. Doses received 5 or more days before the minimum interval or age should be repeated using the correct schedule. Because of the unique accelerated schedule for Twinrix, the 4-day “grace period” does not apply to the first three doses of this vaccine when administered on a 0-, 7-, 21–30-day, and 12-month schedule.

Last reviewed: January 17, 2025

No. No additional doses of pneumococcal vaccine are recommended.

Last reviewed: November 13, 2024

Do not restart the series or give additional doses. The previously administered doses of PCV13 are valid. Complete the pneumococcal conjugate vaccination series with either PCV15 or PCV20 in accordance with the routine schedule.

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.