Ask the Experts: All Questions

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

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Results (1317)

No, gestational diabetes is not classified as a risk factor for acute hepatitis B infection. The increased risk of acute hepatitis B infection has been associated with type 1 and type 2 diabetes; however, all people age 59 years or younger are now recommended to be vaccinated against hepatitis B.

Last reviewed: July 21, 2023

No. The Shingrix vaccine does not count as a vaccination against primary varicella infection (chickenpox). The first varicella vaccine dose can be given at any time after the Shingrix dose. The second dose of varicella vaccine should be given 4 to 8 weeks after the first dose. You should always check the label 3 times to ensure you are administering the product intended.

Last reviewed: March 9, 2022

At this time, ACIP does not recommend revaccination with a second dose of PPSV23 for adults younger than 65 with asplenia who receive PCV15 (Vaxneuvance, Merck) followed by PPSV23.

If the adult patient with asplenia had received PCV13 (Prevnar 13, Pfizer) followed by PPSV23 (instead of Vaxneuvance), then CDC recommends one of two vaccine schedules:

  • Option 1: Administer a dose of PCV20 at least 5 years after the dose of PPSV23. No further doses of pneumococcal vaccine are recommended.
  • Option 2: Administer PPSV23 at least 5 years following the first PPSV23 dose. Plan to review CDC recommendations for pneumococcal vaccination at the time the patient turns 65 because additional doses might be recommended at that point.
Last reviewed: April 5, 2024

Yes, COVID-19 vaccines and other routine vaccines, including influenza and RSV vaccines, may be coadministered on the same day, given in different syringes and at different anatomical sites. COVID-19 vaccines may also be given at any interval before or after any other vaccination.

Of note, there is no required minimum interval between receiving a dose of any COVID-19 vaccine and an orthopoxvirus vaccine, either Jynneos or ACAM2000 vaccine (e.g., for mpox prevention), regardless of which vaccine is administered first. However, use of Jynneos vaccine should be prioritized over ACAM2000 when co-administering a COVID-19 vaccine and an orthopoxvirus vaccine.

People, particularly adolescent or young adult males, who are recommended to be vaccinated against both mpox and COVID-19 might consider waiting 4 weeks between vaccines. This is because of the observed risk for myocarditis and pericarditis after receipt of ACAM2000 orthopoxvirus vaccine and COVID-19 vaccines, and the hypothetical risk for myocarditis and pericarditis after Jynneos vaccine. However, if a patient’s risk for mpox or severe disease due to COVID-19 is increased, administration of mpox and COVID-19 vaccines should not be delayed.

Additional information is available from CDC: www.cdc.gov/vaccines/covid-19/clinical-considerations/interim-considerations-us.html#timing-spacing-interchangeability.

Last reviewed: March 19, 2024

Nirsevimab comes in two single-dose manufacturer-filled syringe (MFS) formulations: 50-mg and 100-mg. Nirsevimab should be stored in the refrigerator between 36°F to 46°F (2°C to 8°C). It may be kept at room temperature 68°F to 77°F (20°C to 25°C) for a maximum of 8 hours. After removal from the refrigerator, nirsevimab must be used within 8 hours or discarded. Store nirsevimab in the original carton to protect it from light until time of use. Do not freeze. Do not shake. Do not expose to heat.

Last reviewed: January 22, 2024

Yes. ACIP recommends a dose of Tdap during each pregnancy irrespective of the patient’s prior history of receiving Tdap. To maximize the maternal antibody response and passive antibody transfer to the infant, optimal timing for Tdap administration is between 27 and 36 weeks’ gestation (preferably early in that window). For more information, see www.cdc.gov/mmwr/volumes/67/rr/pdfs/rr6702a1-H.pdf, pages 22–23.

Last reviewed: March 31, 2022

Since January 2007 the Joint Commission has required accredited organizations to offer annual influenza vaccination to staff, volunteers, and licensed independent practitioners who have close patient contact.

Last reviewed: September 10, 2023

There is no evidence that healthy full-term infants born to women in whom varicella occurs more than 48 hours after delivery are at increased risk for serious complications such as pneumonia or death. Varicella zoster immune globulin, VariZIG, can be given up to 10 days after exposure but is only recommended for newborn infants whose mothers have signs and symptoms of varicella around the time of delivery (5 days before to 2 days after), hospitalized premature infants born at 28 or more weeks of gestation whose mothers do not have evidence of immunity to varicella, or hospitalized premature infants born at less than 28 weeks of gestation or who weigh 1,000 grams or less at birth regardless of their mothers’ evidence of immunity to varicella. Assuming this is an infant at home, VariZIG would not be recommended. Varicella, if it develops, would be managed as for any child.

Last reviewed: May 16, 2023

Although the MMR vaccine package insert recommends a 3-month deferral of pregnancy after MMR vaccination, CDC and ACIP recommend deferral of pregnancy for 4 weeks.

Last reviewed: June 19, 2023

Yes. Data have shown that people acquire hepatitis A virus infection even in such places as 4-star hotels located in Latin America.

Last reviewed: June 25, 2023

A dose less than the full 0.5 mL dose is not valid and should be repeated. If the patient is still in the office the dose can be repeated immediately. If the repeat dose cannot be given on the same day CDC recommends that it should be given 4 weeks after the invalid dose.

Last reviewed: December 28, 2022

The deltoid muscle is recommended for routine intramuscular (IM) vaccination among adults. The anterolateral thigh also can be used. The gluteus muscle should not be used as a site for administering HepB. Please refer to the Immunize.org document Administering Vaccines to Adults: Dose, Route, Site, and Needle Size (available at www.immunize.org/catg.d/p3084.pdf) for complete information on this issue.

Last reviewed: July 21, 2023

A dose less than the full 0.5 mL dose is generally not considered valid and should generally be repeated. If the patient is still in the office the dose can be repeated immediately. If the repeat dose cannot be given on the same day CDC recommends that it should be given 4 weeks after the invalid dose. The provider does have discretion as to whether the amount of vaccine lost is negligible, to make a decision not to repeat the dose of vaccine.

Last reviewed: March 9, 2022

Serologic testing for immunity after HepB vaccination is recommended only for people whose subsequent clinical management depends on knowledge of their immune status. Testing is not necessary after routine vaccination of adults.

Post-vaccination anti-HBs testing of certain adults is recommended for the following reasons:

  • To determine the need for revaccination and the type of follow-up testing:
    • HCP and public safety workers at risk for blood or body fluid exposure
    • Hemodialysis patients (and others who might require outpatient hemodialysis)
    • People with HIV, and other immunocompromised people (e.g., hematopoietic stem-cell transplant recipients or people receiving chemotherapy)
  • To determine the need for revaccination and for other methods of protection against HBV infection:
    • Sex partners or needle-sharing partners of HBsAg-positive people

Testing should be performed 1 to 2 months after the last dose of vaccine.

Last reviewed: July 21, 2023

Either a second PPSV23 or a dose of PCV20 should be given 5 years after the first dose of PPSV23 for people age 19 through 64 years who were vaccinated with PCV13 (Prevnar 13, Pfizer) and PPSV23 and who have one of the following immunocompromising conditions:

  • Kidney disease and on maintenance dialysis
  • Kidney disease with nephrotic syndrome
  • Asplenia or splenic dysfunction
  • Congenital or acquired immunodeficiency, including B-(humoral) or T-lymphocyte deficiency; complement deficiencies, particularly C1, C2, C3, and C4 deficiency; and phagocytic disorders (excluding chronic granulomatous disease)
  • Treatment with immunosuppressive drugs or radiation therapy (including treatment for Hodgkin disease, leukemias, lymphomas, malignant neoplasm, and solid organ transplant)
  • HIV infection
  • Sickle cell disease or other hemoglobinopathies
Last reviewed: April 5, 2024

Every year more healthcare facilities are adopting mandatory vaccination policies for their employees. Immunize.org has included more than 1,330 of these on its Honor Roll for Patient Safety, which gives special recognition to institutions that enforce mandatory vaccination for all personnel who are in the vicinity of a patient (including volunteers and housekeeping staff). To read about the policies of the various facilities included in the Honor Roll, go to www.immunize.org/honor-roll/influenza-mandates/honorees.asp. In addition, the National Adult and Influenza Immunization Summit (NAIIS) has developed tools to assist post-acute and long-term care facilities that plan to implement influenza vaccination requirements for HCP at www.izsummitpartners.org/naiis-workgroups/influenza-workgroup/tools-for-ltcf/. We hope reviewing these policies and tools will give you the information you need to assist in developing a policy for your facility.

Last reviewed: September 10, 2023

No. Seasonal influenza vaccines are reformulated each year; for this reason, all unused seasonal influenza vaccines expire and should be discarded no later than the end of June each season. RSV products (vaccines and preventive antibody) do not change each season and products in your storage unit now may not expire until sometime during or after the next season.

Unless public health authorities advise otherwise, RSV vaccine should not be given during pregnancy after January. Likewise, nirsevimab should not be given to infants after March or before October (unless specifically instructed by public health authorities). Recommendations for timing of RSV vaccination of adults age 60 or older is less precisely defined because vaccination is expected to protect the recipient through two season; however, demand is likely to be lower in spring and summer months. Properly store and clearly label unexpired products remaining in your storage unit during periods when they are not in use and train staff on the timing of these products. Consider storage and labeling that minimizes the risk of mishandling or administration outside the times when the product is recommended to be used.

Last reviewed: January 22, 2024

No. Tdap is an inactivated vaccine and may be administered at the same time as Rhogam (in a separate site with a separate syringe).

Last reviewed: March 31, 2022

No. Just give the final dose of HepA vaccine prior to travel.

Last reviewed: June 25, 2023

Live varicella-containing vaccines (varicella, MMRV) must be stored in a freezer at a temperature between -50°C and -15°C (between -58°F and +5°F) until reconstitution and administration. These vaccines can deteriorate rapidly after they are removed from the freezer. A separate stand-alone freezer or a combination refrigerator-freezer purpose-built for vaccine storage (sometimes called “pharmaceutical grade”) should be used to store frozen vaccines that require storage temperatures between -50°C and -15°C (between -58°F and +5°F). A stand-alone storage unit that is frost-free or has an automatic defrost cycle is preferred. Frozen vaccines should not be stored in the freezer compartment of a household-type combination unit because household freezers in combination units cannot reliably maintain proper storage temperatures for frozen vaccines. This applies to both temporary and long-term storage of frozen vaccines. The diluents should be kept separately in the refrigerator or at room temperature. Live varicella-containing vaccines must be administered within 30 minutes of reconstitution.

Last reviewed: May 16, 2023

ACIP recommends that people capable of bearing children be asked if they are currently pregnant or attempting to become pregnant. Vaccination should be deferred for those who answer “yes.” Those who answer “no” should be advised to avoid pregnancy for 4 weeks following vaccination. Pregnancy testing is not necessary.

Last reviewed: June 19, 2023

The CDC zoster subject matter experts recommend that in this situation you should wait 4 weeks before giving a repeat dose.

Last reviewed: December 28, 2022

The CDC zoster subject matter experts recommend that in this situation you should wait 4 weeks before giving a repeat dose.

Last reviewed: March 9, 2022

Your patient may choose to receive the vaccines at the same visit or separately, without regard to the timing interval. In general, when deciding whether to coadminister other vaccines with COVID-19 vaccine, you should consider whether the patient is behind or at risk of becoming behind on recommended vaccines, their risk of vaccine-preventable disease (e.g., during an outbreak or occupational exposures), and the reactogenicity profile of the vaccines.

When multiple vaccines are administered at a single visit, administer each injection in a different syringe and at a different injection site. For adolescents and adults, the deltoid muscle may be used for more than one injection, though injection sites should be at least one inch apart. It is generally preferable to administer reactogenic vaccines such as Shingrix and COVID-19 vaccine in different arms, if possible. If the patient prefers both injections in the same deltoid, that is also acceptable.

Immunize.org has developed a one-page guide to administering multiple intramuscular vaccinations to an adult at one visit: www.immunize.org/catg.d/p2030.pdf.

Last reviewed: March 19, 2024

Perhaps. CDC recommends two options for people age 65 or older who have immunocompromising conditions, a cochlear implant, or a cerebrospinal fluid (CSF) leak and received PCV13 and either one or two doses of PPSV23 before age 65:

  • Option 1: Give a dose of PCV20 at least 5 years after the last pneumococcal vaccine dose
  • Option 2: Give a dose of PPSV23 at least 8 weeks after PCV13 and at least 5 years after the previous PPSV23 dose

A patient age 65 or older who received one or two doses of PPSV23 before age 65 but has not received any PCV product, or their history of PCV vaccination is unknown, is recommended to receive a single dose of either PCV15 or PCV20 at least one year after the last dose of PPSV23.

Last reviewed: April 5, 2024

No specific action needs to be taken other than to reassure the pregnant person that no adverse outcomes are expected as a result of this vaccination. MMR vaccination during pregnancy is not a reason to terminate the pregnancy. You should consult with others in your healthcare setting to identify ways to prevent such vaccination errors in the future. Detailed information about MMR vaccination in pregnancy is included in the 2013 MMR ACIP statement, available at www.cdc.gov/mmwr/pdf/rr/rr6204.pdf.

Last reviewed: June 19, 2023

Children, age 7 years and older, and adults who have never received tetanus-containing vaccines, or whose vaccination history is unknown, should receive the 3-dose series. In this situation, ACIP recommends Tdap for dose #1, followed 4 weeks later by Td or Tdap for dose #2, followed at least 6 months later by Td or Tdap for dose #3. The amount of protection provided by one or more doses of Tdap in a person who has not previously received pertussis vaccine is not known. Following the primary series, booster doses of Td or Tdap should be given every 10 years thereafter.

Last reviewed: March 31, 2022

Possibly. Since IG protects against hepatitis A infection for only 1 to 2 months, depending on the dosage given, additional IG may be needed if the infant is not yet age 6 months. Once the child has reached six months of age, HepA vaccine should be given.

Last reviewed: June 25, 2023

Though vaccination is the most effective means of protecting your patients from influenza, there may be instances where employees are not vaccinated for medical or personal reasons. In these instances, you may want to consider reassigning unvaccinated workers to non-patient areas or requiring that they wear masks throughout the influenza season.

Last reviewed: September 10, 2023

Vaccine may lose potency rapidly if not stored according to the manufacturer’s instructions. However, it may still be permissible to use vaccine that has not been properly stored. Put the affected vaccine vials into the freezer after you have marked them so they are not confused with the unaffected vials, then call the manufacturer at 1-800-9-VARIVAX (1-800-982-7482) for further guidance about whether the vaccine is still usable. Unreconstituted varicella vaccine may be stored in the refrigerator for up to 72 hours before use. If refrigerated varicella vaccine is not used within 72 hours, it should be discarded.

If you have inadvertently left your vaccine at room temperature instead of in the freezer or have experienced a power failure, label the affected vaccine to keep it separated from unaffected vaccine and return it to recommended storage conditions in a freezer promptly, then contact the manufacturer for further guidance. Do not administer the vaccine until you have consulted with Merck.

Last reviewed: May 16, 2023

Any RZV, either antigen or diluent, that is exposed to freezing temperature should not be used. If a dose exposed to freezing temperature is given to a patient the dose should be considered invalid and should be repeated 4 weeks after the invalid dose.

Last reviewed: December 28, 2022

Sexually transmitted infections, including hepatitis B, can be transmitted by sexual assault. Unless the victim has a documented history of completed HepB vaccination, a series of HepB alone (2 or 3 doses depending on brand) should be administered with the first dose as soon as possible after the assault. Administration of hepatitis B immune globulin (HBIG) is not necessary.

Last reviewed: July 21, 2023

Any Shingrix, either antigen or diluent, that is exposed to freezing temperature should not be used. If a dose exposed to freezing temperature is given to a patient the dose should be considered invalid and should be repeated 4 weeks after the invalid dose.

Last reviewed: March 9, 2022

The vaccine manufacturer does not recommend transporting varicella-containing vaccines (varicella, MMRV). If these vaccines must be transported (for example during an emergency), CDC recommends use of a portable vaccine freezer unit or qualified container and packout that maintains temperatures between -50°C and -15°C (- 8°F and +5°F). Do not use dry ice, even for temporary storage. Dry ice might expose the vaccines to temperatures colder than -50°C (-58°F), resulting in compromise of the vial stopper material.

Follow these steps for transporting frozen vaccines:

  • Place a temperature monitoring device (preferably with a buffered probe) in the container as close as possible to the vaccines.
  • Immediately upon arrival at the destination, unpack the vaccines and place them in a freezer at a temperature range between -50°C and -15°C (-58°F and +5°F). Any stand-alone freezer or freezer purpose built for vaccine storage that maintains these temperatures is acceptable.
  • Record the time vaccines are removed from the storage unit and placed in the transport container, the temperature during transport, and the time at the end of transport when vaccines are placed in a stable storage unit.

If necessary, varicella-containing vaccines may be transported or stored at refrigerator temperature between 2°C and 8°C (between 36°F and 46°F) for up to 72 continuous hours prior to reconstitution. To do so, follow the steps above using a portable vaccine refrigerator unit or a qualified container and packout designed to maintain vaccine storage temperatures between 2°C and 8°C (between 36°F and 46°F).

Transport of varicella-containing vaccine at temperatures other than the recommended range between -50°C and -15°C (-58°F and +5°F) is considered a temperature excursion, so contact Merck at (800) 982-7482 for further guidance. Do not discard vaccines without contacting the manufacturer and/or your immunization program for guidance.

For additional guidance, see the CDC Vaccine Storage and Handling Toolkit at www.cdc.gov/vaccines/hcp/admin/storage/toolkit/storage-handling-toolkit.pdf.

Last reviewed: May 16, 2023

If a vaccine is covered under the National Childhood Vaccine Injury Act—and almost all vaccines routinely administered to adults are (with the exception of PPSV and zoster)—it is mandatory under federal law to give the VIS for that vaccine to the vaccinee. Therefore, when you give influenza vaccine to employees and staff, you are required by law to provide them with a VIS.

Last reviewed: September 10, 2023

No. ACIP does not recommend revaccination with PPSV23 for any adult who has received a dose of PPSV23 after turning 65. However, this patient should receive a dose of either PCV15 or PCV20 now.

Last reviewed: April 5, 2024

The timing of CDC-recommended vaccination is unaffected by the receipt of COVID-19 monoclonal antibodies or convalescent plasma.

Last reviewed: March 19, 2024

The fourth dose of DTaP may be given as early as age 12 months if at least 6 months have passed since the third dose.

Last reviewed: March 31, 2022

No. ACIP recommends that anyone capable of bearing children be asked if they are currently pregnant or attempting to become pregnant. Vaccination should be deferred for those who answer “yes.” Those who answer “no” should be advised to avoid pregnancy for one month following vaccination.

Last reviewed: June 19, 2023

Yes. ACIP recommends that all children age 1 year through 18 years should be vaccinated against hepatitis A. VFC HepA vaccine may be administered to any eligible child, including those recommended for vaccination at 6 through 11 months of age as a result of travel to an HAV-endemic area.

Last reviewed: June 25, 2023

Neither the Advisory Committee on Immunization Practices (ACIP) nor the manufacturers address the timing of vaccination and dialysis. People with end-stage renal disease including predialysis, hemodialysis, peritoneal dialysis, and home dialysis should be tested for hepatitis B surface antibody (anti-HBs) 1–2 months after vaccination, and annually. If the anti-HBs level is below 10mIU/mL, they should be revaccinated.

Last reviewed: July 21, 2023

Both lyophilized Shingrix and the adjuvant solution diluent must be stored at refrigerator temperature, between 2° and 8°C (between 36° and 46°F). Protect the vials from light. Do not freeze. Vaccine or adjuvant solution that has been frozen must be discarded. If vaccine that was frozen was administered, the dose does not count and should be repeated. The repeat dose should be administered 4 weeks after the frozen dose. After reconstitution, administer Shingrix immediately or store refrigerated between 2° and 8°C (between 36° and 46°F) and use within 6 hours. Discard reconstituted vaccine if not used within 6 hours.

Last reviewed: March 9, 2022

Shingrix is stored at refrigerator temperature. Transport of refrigerated vaccines is described in detail in the CDC Storage and Handling Toolkit, available at www.cdc.gov/vaccines/hcp/admin/storage/toolkit/storage-handling-toolkit.pdf, pages 22–24. Providers should also review the vaccine package inserts for the specific vaccines being transported.

Last reviewed: March 9, 2022

Yes. There are more than 100 known serotypes of pneumococcus. Infection with one serotype does not necessarily produce immunity to other serotypes. As a result, if the person is a candidate for vaccination, they should receive it even after one or more episodes of pneumococcal disease.

Last reviewed: April 5, 2024

You should try to achieve at least 4 total doses. Give additional doses of DTaP with 4-week intervals until you achieve 3 total doses. Then, if 6 months pass and the child has not turned seven years old, give the 4th dose of DTaP: if the child has turned seven years old, you may administer a dose of Tdap vaccine at that time.

Last reviewed: March 31, 2022

It depends on whether that person has a history of HAV infection. Unless there are medical records that document prior HAV infection, serologic testing for immunity (positive test for total anti-HAV) is the only way to determine if vaccination is necessary. For people from countries with high rates of HAV infection, such as Vietnam and Mexico, serologic testing might be done to prevent unnecessary vaccination. The cost effectiveness of serologic testing, however, should be balanced against the possibility of delaying needed vaccination while awaiting test results.

Last reviewed: June 25, 2023

Yes. According to the manufacturer, unreconstituted varicella vaccine may be stored at refrigerator temperature (2°C to 8°C, 36°F to 46°F) for up to 72 continuous hours prior to reconstitution. Vaccine stored at 2°C to 8°C that is not used within 72 hours of removal from -15°C (+5°F) storage should be discarded. See www.merck.com/product/usa/pi_circulars/v/varivax/varivax_pi.pdf.

Last reviewed: May 16, 2023

Some studies have shown an increase in HCP influenza vaccine acceptance when decliners are required to sign such a statement. In addition, such statements can help a vaccination program assess the reasons for declination and plan future educational efforts. Immunize.org has posted the following suggested declination form for healthcare workers at www.immunize.org/catg.d/p4068.pdf.

Last reviewed: September 10, 2023

Yes. Measles, mumps, and rubella vaccine viruses are not transmitted from the vaccinated person, so MMR vaccination of a household contact does not pose a risk to a pregnant household member.

Last reviewed: June 19, 2023

Recommendations for immunocompromised people, such as hemodialysis patients, are different than those for immunocompetent people. Hemodialysis patients who do not respond to an initial vaccine series should be revaccinated with two to four additional doses of HepB (depending on the brand). Hemodialysis patients are considered immune as long as they have adequate anti-HBs (at least 10 mIU/mL). For hemodialysis patients who have responded with adequate anti-HBs (postvaccination testing should be done 1 to 2 months after the vaccine series) to HepB vaccination, no HBsAg testing is needed but anti-HBs should be done annually. If anti-HBs declines below 10 mIU/mL, a booster dose of HepB should be given and annual anti-HBs testing should be continued. Retesting immediately after the booster dose is not necessary.

Last reviewed: July 21, 2023

There are many professional associations that have issued policy statements supporting mandatory healthcare worker influenza vaccination. You can find information about these organizations as well as a list of more than 1,330 healthcare settings that have implemented mandatory vaccination programs on Immunize.org’s website at Immunize.org’s Influenza Vaccination Honor Roll web section at www.immunize.org/honor-roll/influenza-mandates/.

Last reviewed: September 10, 2023

In 2013, ACIP updated its recommendation for this situation (see www.cdc.gov/mmwr/pdf/rr/rr6204.pdf, pages 18–20). It is recommended that people capable of bearing children who have received 1 or 2 doses of rubella-containing vaccine and have rubella serum IgG levels that are not clearly positive should be administered 1 additional dose of MMR vaccine (maximum of 3 doses) and do not need to be retested for serologic evidence of rubella immunity. MMR should not be administered to a pregnant person.

Last reviewed: June 19, 2023

Although the child would be considered complete for tetanus and diphtheria toxoids, she is not complete for pertussis vaccine. DTaP vaccines are FDA-approved only through age 6 years so no more DTaP doses are recommended.

However, ACIP recommends that children age 7–10 years who are not fully vaccinated against pertussis (defined as 5 doses of DTaP or 4 doses of DTaP if the fourth dose was administered on or after the fourth birthday) and who do not have a contraindication to pertussis vaccine should receive a single dose of Tdap to provide protection against pertussis. If the child in this case is age 7–9 years at the time of Tdap vaccination, the next dose due will be the routine adolescent dose of Tdap at age 11 or 12 years. If the child is age 10, the dose counts as the adolescent dose and no additional dose at age 11 or 12 years is recommended.

Last reviewed: March 31, 2022

No, as long as there are medical records that document that the person was previously infected with HAV (i.e., positive test for total anti-HAV). If there is any doubt that the person actually was infected with HAV, HepA vaccine and/or IG should be given. The vaccine or IG will not harm a person who is already immune.

Last reviewed: June 25, 2023

Influenza virus is easily spread from healthcare workers to their patients, and infection usually leads to clinical illness. Pneumococcus is probably not spread from healthcare workers to their patients as easily as is influenza, and infection with pneumococcus does not necessarily lead to clinical illness. Host factors (such as age, underlying illness) are more important in the development of invasive pneumococcal disease than nasopharyngeal colonization with the organism.

Last reviewed: April 5, 2024

There is no maximum number of HepB booster doses a dialysis patient can receive. Serology should be performed once a year and a booster dose given if serology is negative (less than 10 mIU/mL). Serology is not recommended more frequently than once a year, so boosters wouldn’t be given more than once a year.

Last reviewed: July 21, 2023

Contraindications to egg-based inactivated influenza vaccines (IIV) are a severe allergic reaction to a prior dose of any influenza vaccine (any egg-based IIV, ccIIV, RIV, or LAIV of any valency) or a severe allergy to an influenza vaccine component (except egg). ACIP recommends that people with egg allergy of any severity may receive any influenza vaccine appropriate for their age and health status.

Precautions to egg-based IIV include moderate or severe acute illness, and history of Guillain-Barré syndrome within 6 weeks after a dose of influenza vaccine.

Contraindications to ccIIV4 are a history of a severe allergic reaction or any component of ccIIV4.

Precautions to ccIIV4 are moderate or severe acute illness, a history of Guillain-Barré syndrome within 6 weeks after a dose of influenza vaccine, and a history of a severe allergic reaction to a previous dose of any other influenza vaccine (e.g., any egg-based IIV, RIV, or LAIV).

Contraindications to RIV4 are a history of a severe allergic reaction or any component of RIV4.

Precautions to RIV4 are moderate or severe acute illness, a history of Guillain-Barré syndrome within 6 weeks after a dose of influenza vaccine, and a history of a severe allergic reaction to a previous dose of any other influenza vaccine (e.g., any egg-based IIV, ccIIV, or LAIV).

Last reviewed: September 10, 2023

Yes. If given on the same day as separate injections in separate sites, two injections of Engerix-B 20 mcg can be counted as the equivalent of one Recombivax HB 40-mcg dose. According to the package insert, Engerix-B is licensed for use in this manner (vaccine package inserts for all vaccines are available at www.immunize.org/fda). Note that an all-Engerix-B or mixed-brand dialysis schedule is a 4-dose series (doses at 0, 1, 2, and 6 months). Vaccination using only Recombivax HB dialysis formulation is a 3-dose schedule (doses at 0, 1, and 6 months). Heplisav-B and PreHevbrio have not been evaluated for use in dialysis patients.

Last reviewed: July 21, 2023

PCV vaccines are conjugated to a type of diphtheria toxoid. If someone has a past history of anaphylaxis following diphtheria-containing vaccine, it might be due to the diphtheria toxoid, and the cause of the anaphylactic allergy should be identified before the administration of a PCV vaccine. This could be difficult since no single-antigen diphtheria toxoid is available in the U.S. Fortunately, true anaphylactic allergy to diphtheria-containing vaccine is rare.

Last reviewed: April 5, 2024

Yes, they may be vaccinated with any FDA-licensed or FDA-authorized updated (2023–2024 Formula) COVID-19 vaccine (Moderna, Pfizer, or Novavax) as long as they do not have a contraindication to vaccination. Antibody testing is not recommended to assess for immunity to SARS-CoV-2 following COVID-19 vaccination.

Recipients should be counseled about the unknown and variable effectiveness of COVID-19 vaccination in immunocompromised populations and the potential for reduced immune responses. They may consider other practices to reduce their risk of infection. CDC has published additional information about respiratory virus prevention for people with weakened immune systems: www.cdc.gov/respiratory-viruses/risk-factors/weakened-immune-systems.html.

CDC has developed an infographic for use with patients who have moderate to severe immunocompromise when determining what updated (2023–2024 Formula) COVID-19 vaccine is due based on the individual’s age and past COVID-19 vaccination history: www.cdc.gov/vaccines/covid-19/downloads/COVID19-vaccination-recommendations-immunocompromised.pdf.

CDC provides detailed considerations for vaccination of people with moderate or severe immunocompromise here: www.cdc.gov/vaccines/covid-19/clinical-considerations/interim-considerations-us.html#immunocompromised.

Last reviewed: March 19, 2024

If DTaP #4 is given with at least a 4-month interval after DTaP #3, it does not need to be repeated. The minimum age of 12 months for the fourth dose must be met. Decreasing the interval to less than 6 months, however, is not recommended.

Last reviewed: March 31, 2022

A severe allergic reaction to any influenza vaccine is a contraindication to receiving additional doses of the same vaccine or receiving any egg-based influenza vaccines. The following table summarizes the contraindications and precautions for different types of influenza vaccine and is adapted from table 3 of the 2022–23 influenza ACIP recommendations at www.cdc.gov/mmwr/volumes/71/rr/pdfs/rr7101a1-H.pdf:

Vaccine (of any valency) associated with previous serious or anaphylactic reaction Available 2022–23 influenza vaccines
Egg-based IIV4s
and LAIV4		 Cell-culture- based IIV4: ccIIV4 (Flucelvax) Recombinant IIV4: RIV4 (Flublok)
Any egg-based IIV or LAIV Contraindication Precaution † Precaution †
Any ccIIV Contraindication Contraindication Precaution †
Any RIV Contraindication Precaution † Contraindication
Unknown influenza vaccine Allergist consultation recommended

† Note regarding patients having either of the above precautions for either ccIIV or IIV: use of ccIIV4 and RIV4 in such instances should occur in an inpatient or outpatient medical setting under the supervision of a healthcare provider (HCP) who can recognize and manage severe allergic reaction; HCPs can also consider consulting with an allergist to help identify the vaccine component responsible for the reaction.

Last reviewed: September 10, 2023

ACIP recommends that vaccinated people of childbearing age who have received one or two doses of rubella-containing vaccine and have a rubella serum IgG levels that is not clearly positive should be administered one additional dose of MMR vaccine (maximum of three doses). Repeat serologic testing for evidence of rubella immunity is not recommended. See www.cdc.gov/mmwr/pdf/rr/rr6204.pdf, pages 18–20, for more information on this issue.

MMR vaccines should not be administered to people known to be pregnant or attempting to become pregnant. Because of the theoretical risk to the fetus when the mother receives a live virus vaccine, people capable of bearing children should be counseled to avoid becoming pregnant for 28 days after receipt of MMR vaccine.

Last reviewed: June 19, 2023

This page was updated on .

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