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 (1374)

All foreign-born people (including immigrants, refugees, asylum seekers, and internationally adopted children) born in Asia, the Pacific Islands, Africa, and other regions with high or intermediate endemicity of HBV infection should be tested for HBsAg, regardless of vaccination status. Initiating HepB vaccination of immigrant children should not be delayed while awaiting HBsAg test results: you may draw blood for testing then administer the first dose of vaccine at the same visit. All people found to be HBsAg-positive should have ongoing medical management by a physician knowledgeable about hepatitis B and its complications.

Last reviewed: January 17, 2025

A person who is not moderately or severely immunocompromised and received a single dose of Novavax COVID-19 vaccine more than 2 months ago may receive a single dose of any licensed or authorized 2024–2025 Formula COVID-19 vaccine, including Novavax.

Last reviewed: November 16, 2024

In April 2022, CDC published updated recommendations from the Advisory Committee on Immunization Practices (ACIP) for the use of hepatitis B vaccine (HepB) in adults. In addition to routine universal childhood HepB vaccination, CDC now recommends catch-up vaccination of all adults younger than age 60 years not previously vaccinated. CDC also recommends that healthcare providers offer HepB vaccination to all adults age 60 or older and routinely given to any adult in this age group known to be at risk. Access the ACIP recommendation: www.cdc.gov/mmwr/volumes/71/wr/pdfs/mm7113a1-H.pdf.

Last reviewed: January 17, 2025


1:17

View All Video Questions

Last reviewed: December 7, 2023

In March 2023, CDC published updated hepatitis B screening and testing guidelines for all adults age 18 years or older. In brief, it is recommended that all adults should be serologically screened for hepatitis B at least one time using a triple panel test, regardless of vaccination history. The triple panel includes antibody
to hepatitis B surface antigen (anti-HBs), total core antibody (anti-HBc), and surface antigen (HBsAg). Pregnant people should be tested for HBsAg during each pregnancy, regardless of testing or vaccination history. After the one-time screening, unvaccinated, susceptible individuals at ongoing risk should be tested periodically for infection. In addition, anyone who requests testing should be tested. Access the CDC recommendations: www.cdc.gov/mmwr/volumes/72/rr/pdfs/rr7201a1-H.pdf.

Last reviewed: January 17, 2025

Anyone can be infected with hepatitis B. Everyone can benefit from knowing their status and being protected. The majority of adults reported to CDC in recent years with acute hepatitis B have no reported risk factor for infection. Risk factors for exposure are so numerous and diverse that most adults, even those who don’t think of themselves as at risk, may find themselves at risk at some point in their lives.

Infants and children have been routinely vaccinated since the 1990s. As a result, we see very little hepatitis B in the routinely vaccinated age groups; however, rates have been steady or rising in unvaccinated older adults. CDC recommends extending this vaccine protection to all adults in a catch-up vaccination program. This is a crucial step toward the goal of eliminating hepatitis B and the liver disease and cancer it causes.

Last reviewed: January 17, 2025


1:47

View All Video Questions

Last reviewed: December 7, 2023

According to the American Pharmacist Association, all states allow pharmacists to administer zoster vaccine. Not all pharmacists provide vaccination services, and of those who do, not all administer zoster vaccine. It is best to call the pharmacy ahead of time to find out if they have Shingrix to administer to your patients. The vaccine must be administered in the pharmacy. Do NOT instruct the patient to transport the vaccine from the pharmacy back to your office. This could damage the potency of the vaccine.

Last reviewed: March 9, 2022

Varicella zoster immune globulin (VariZIG, Saol Therapeutics) is a human blood product prepared from plasma obtained from healthy, volunteer blood donors identified by routine screening to have high antibody titers to varicella-zoster virus. The first varicella zoster immune globulin, VZIG, became available in 1978. In a study of immunocompromised children who were administered VZIG within 96 hours of exposure, approximately one in five exposed children developed clinical varicella, and one in 20 developed subclinical disease compared with 65%—85% attack rates among historical controls. In 2006, VZIG was discontinued and a new product, VariZIG, became available.

Last reviewed: May 16, 2023

No, it is not recommended to give another dose of Tdap in such cases. Optimal timing for Tdap administration is between 27 and 36 weeks’ gestation because that stage of pregnancy is best for transplacental antibody movement to the fetus.

More information is available at www.cdc.gov/mmwr/volumes/67/rr/pdfs/rr6702a1-H.pdf, pages 22–23.

Last reviewed: March 31, 2022

Hepatitis A vaccination is recommended for people age 6 months or older who are traveling to or working in an area of the world at intermediate or high risk of hepatitis A transmission. Areas of low risk include the United States, Canada, Japan, New Zealand, Australia and Western Europe. Visit the CDC’s Traveler Health website for more information about specific destinations and current outbreaks or travel notices (https://wwwnc.cdc.gov/travel/). When in doubt, vaccinate.

Last reviewed: June 25, 2023

PPSV23 is not effective in children younger than 24 months of age. PPSV23 given at this age should not be considered to be part of the pneumococcal vaccination series. Pneumococcal conjugate vaccine should be administered as soon as the error is discovered. Any time the wrong vaccine is given, the parent/patient should be notified.

Last reviewed: December 28, 2022

Yes. Breastfeeding does not interfere with the response to MMR vaccine. Vaccination of a woman who is breastfeeding poses no risk to the infant being breastfed. Although it is believed that rubella vaccine virus, in rare instances, may be transmitted via breast milk, the infection in the infant is asymptomatic.

Last reviewed: June 19, 2023

We encourage HCPs to stay home from work when they are sick. Unfortunately, by the time a HCP has symptoms of influenza, they may have already exposed many patients since the virus is shed for 1–2 days before symptoms begin. Further, many studies show that HCP often go to work while they are sick and may be infectious to others. Start planning early to make sure all employees in your work setting receive annual influenza vaccination before the influenza season begins.

Last reviewed: August 11, 2024

Yes. V-safe is a vaccine safety monitoring system that lets recipients of certain new vaccines share with CDC how they feel after vaccination by receiving and responding to a series of periodic text messages. This is a voluntary system and individual recipients must register to participate V-safe. V-safe is available to Arexvy (GSK) and Abrysvo (Pfizer) RSV vaccine recipients.  At this time, V-safe is not being used for mResvia (Moderna) or for nirsevimab preventive antibody (Beyfortus, Sanofi). For information, or to register, visit CDC’s V-safe website at: www.cdc.gov/vaccine-safety-systems/v-safe/index.html.

Last reviewed: August 25, 2024

Recommendations for adult dialysis patients vary by age and pneumococcal conjugate (PCV) or polysaccharide (PPSV23) vaccination history:

  • Adult dialysis patients who have not previously received pneumococcal vaccination should receive either PCV20 or PCV21 alone or a series of PCV15 followed by PPSV23 at least 8 weeks later. No further pneumococcal vaccines are recommended. 
  • Adult dialysis patients who are age 19 through 49 and have already received one dose of PPSV23 may receive one dose of any currently recommended PCV (PCV15, PCV20, or PCV21) one year after the dose of PPSV23; no further doses of PPSV23 are recommended. 
  • Adult dialysis patients who are 50 or older and who have received PCV13 and PPSV23 in the past should receive one dose of PCV20 or PCV21 at least 5 years after the last pneumococcal vaccination.  
  • Adult dialysis patients who received PCV13 at any point and also received a PPSV23 vaccination after turning 65 are not routinely recommended to receive any additional doses of pneumococcal vaccine. They have the option to receive a dose of PCV20 or PCV21 at least 5 years after their most recent pneumococcal vaccination on the basis of shared clinical decision-making, based upon their risk of pneumococcal disease and desire for additional protection. 
Last reviewed: November 13, 2024

Heplisav-B (Dynavax, 2-dose series), and Twinrix (GSK, combination HepA-HepB, 3-dose series) are approved for adults age 18 years and older. Engerix-B (GSK) and Recombivax HB (Merck), both administered as a 1.0 mL 3-dose series, are approved for adults age 20 years and older; young adults who are age 19 receive the 0.5 mL pediatric dose of Engerix-B and Recombivax HB. PreHevbrio (VBI, 3-dose series), was available and used in adults age 18 years and older between 2021 and 2024 before it was removed from the market following the bankruptcy of its manufacturer.

Last reviewed: January 17, 2025

CDC recommends that if a provider mistakenly administers varicella vaccine to a person for whom zoster vaccine is indicated, no specific safety concerns exist, but the dose should not be considered valid. You should administer a dose of Shingrix to the patient during that same visit (same day). If the error is not detected and corrected on the same day, Shingrix should be administered at least 8 weeks after receipt of the varicella vaccine. However, if Shingrix is administered less than 8 weeks after the varicella vaccine, it does not need to be repeated. A second dose of Shingrix should be given 2–6 months after the first dose of Shingrix.

These events should be documented and procedures put in place, such as checking the vial label 3 times to be sure you are administering the product you intend, to prevent this from happening again.

Last reviewed: March 9, 2022

Yes, but there should be sufficient time between the blood product and the MMR to reduce the chance of interference. The interval depends on the blood product received. See Table 3-6 of ACIP’s “General Best Practice Guidelines for Immunization” for more information, available at www.cdc.gov/vaccines/hcp/acip-recs/general-recs/timing.html.

Last reviewed: June 19, 2023

Although PCV and PPSV23 should not be administered at the same visit, CDC does not recommend repeating either vaccine dose should this occur. You should inform the patient of the error and let them know that they will not need to repeat either dose.

Last reviewed: December 28, 2022

ACIP does not recommend repeated doses of Tdap for fathers or other family members or caregivers of infants during every pregnancy. The recommendation for Tdap vaccination with each pregnancy to optimize immunity for the infant applies only to the pregnant mother.

The practice of “cocooning” infants by making a particular effort to vaccinate caregivers who have not received Tdap vaccination has been recommended by ACIP since 2005; however, the practice has been difficult to implement fully and may not be effective alone as a strategy for protecting newborns from pertussis exposure. The combined strategy of Tdap vaccination during each pregnancy, cocooning, and administering the childhood DTaP series on schedule provides the best protection to the infant.

Last reviewed: March 31, 2022

For details on preexposure protection of international travelers age 12 months and older, refer to Appendix A on page 35 of the current ACIP recommendations for the prevention of hepatitis A: www.cdc.gov/mmwr/volumes/69/rr/pdfs/rr6905a1-H.pdf.

Healthy people age 12 months through 40 years who are planning travel to an area with high or intermediate HAV endemicity and have not received HepA vaccine should receive a single dose of HepA vaccine as soon as travel is considered and should complete the 2-does series according to the routine schedule.

People with chronic liver disease as well as adults older than 40 years of age, immunocompromised people, and people with other chronic medical conditions planning to depart to an area with high or intermediate HAV endemicity in less than 2 weeks should receive the initial dose of HepA vaccine and may also simultaneously be administered immune globulin (IG) at a separate anatomic injection site (for example in separate limbs).

ACIP revised its recommendations for preexposure hepatitis A vaccination for travelers in 2018 to include vaccination of infants 6 through 11 months of age. All infants of this age traveling internationally should be given a dose of measles, mumps, rubella vaccine (MMR) before travel. Due to the potential interference of hepatitis A IG with MMR vaccine effectiveness, an off-label dose of HepA vaccine is recommended instead of IG in this situation. The travel-related dose for infants 6–11 months of age should not be counted toward the routine 2-dose series. The routine 2-dose HepA and MMR vaccination series should be initiated at age 12 months according to the routine, age-appropriate vaccination schedule.

Infants younger than 6 months and travelers who elect not to receive vaccine or for whom vaccine is contraindicated should receive a single 0.1 mL/kg dose of IG before travel when protection against HAV is recommended. If travel is for more than 1 month, a dose of 0.2 mL/kg should be administered. A 0.2 mL/kg dose can be repeated every 2 months for travel of more than 2 months duration.

Last reviewed: June 25, 2023

Because HCP provide care to patients at high risk for complications of influenza, they should be considered a high-priority group for receiving vaccination. Achieving high rates of vaccination among HCP will protect staff and their patients and reduce disease burden and healthcare costs.

In 2011, ACIP published “Immunization of Health-Care Personnel,” which includes information about all recommended vaccines (see www.cdc.gov/mmwr/pdf/rr/rr6007.pdf).

Last reviewed: August 11, 2024

Nirsevimab (Beyfortus, Sanofi) is contraindicated in persons with a history of severe allergic reactions (e.g., anaphylaxis) after a previous dose or to a product component. As with any injection, when administering nirsevimab to children with increased risk for bleeding, providers should follow ACIP’s general best practice guidelines for immunization.

Last reviewed: August 25, 2024

CDC’s guidance is to ignore the remote history of PCV7 and evaluate the patient as if he has never had pneumococcal vaccination. The patient should receive PCV20 or PCV21 alone or PCV15 in series with PPSV23 given at least one year later. If using PCV15, and if the high-risk condition is immunocompromising or if the patient has a cochlear implant or cerebrospinal fluid leak, you may consider administering the PPSV23 as soon as 8 weeks after PCV15.

Last reviewed: November 13, 2024

Everyone age 6 months and older is recommended to receive at least one dose of 2024–2025 Formula COVID-19 vaccine, regardless of past vaccination history. Any 2024–2025 Formula COVID-19 vaccine received in another country that is listed for emergency use by the World Health Organization (WHO-EUL) or authorized or licensed for use by the FDA counts toward fulfilling this recommendation. If you cannot determine whether the dose received was a 2024–2025 Formula COVID-19 vaccine, then do not count the dose and proceed with vaccination.

CDC has provided additional details based upon age and immunocompromised status at its website: www.cdc.gov/vaccines/covid-19/clinical-considerations/interim-considerations-us-appendix.html#appendix-a.

A list of the vaccines that have already received WHO-EUL status is available here: https://extranet.who.int/prequal/vaccines/covid-19-vaccines-who-emergency-use-listing.

Last reviewed: November 16, 2024

In general, one HepB series is needed in a lifetime, with rare exceptions described at the end of this answer.

As of April 2022, CDC recommends HepB vaccination of all adults age 60 or older who are in any of the following risk groups (vaccination also may be offered and administered to anyone age 60 and older, regardless of risk):

  • All adults age 60 years and older with risk factors for hepatitis B:
    • People at risk for infection by sexual exposure
      • Sex partners of people testing positive for HBsAg
      • Sexually active people who are not in a long-term, mutually monogamous relationship (e.g., those with more than one sex partner during the previous 6 months)
      • People seeking evaluation or treatment for a sexually transmitted infection
      • Men who have sex with men
    • People at risk for infection by percutaneous or mucosal exposure to blood
      • People with current or recent injection drug use
      • Household contacts of people testing positive for HBsAg
      • Residents and staff members of facilities for people with developmental disabilities
      • Healthcare and public safety personnel with reasonably anticipated risk for exposure to blood or blood-contaminated body fluids
      • People on maintenance dialysis, including in-center or home hemodialysis and peritoneal dialysis, and people who are predialysis
      • People with diabetes, at the discretion of the treating clinician
    • Others
      • International travelers to countries with high or intermediate levels of endemic hepatitis B virus (HBV) infection (HBsAg prevalence of 2% or higher)
      • People with hepatitis C virus infection
      • People with chronic liver disease (including, but not limited to, people with cirrhosis, fatty liver disease, alcoholic liver disease, autoimmune hepatitis, and an alanine aminotransferase or aspartate aminotransferase level greater than twice the upper limit of normal)
      • People with HIV infection
      • People who are incarcerated

The official CDC recommendations for HepB vaccination of adults are available at www.cdc.gov/mmwr/volumes/71/wr/pdfs/mm7113a1-H.pdf. Immunize.org has developed a standing order template for adult HepB vaccination: www.immunize.org/catg.d/p3076.pdf.

In general, people who have documented completion of a HepB series at any point or who have a history of previous HBV infection should not receive additional HepB vaccination, although there is no evidence that additional vaccination is harmful. In settings where the patient population has a high rate of previous HBV infection, prevaccination testing, which may be performed at the same visit when the first dose of vaccine is administered, might reduce costs by avoiding complete vaccination of people who are already immune. However, prevaccination testing is not required and should not create a barrier to vaccination.

Revaccination may be indicated for certain high-risk adults, including healthcare workers who are documented non-responders to an initial HepB series, and certain people who receive dialysis or who are immunocompromised. For specific revaccination guidance, see the 2018 ACIP recommendations for the prevention of hepatitis B at www.cdc.gov/mmwr/volumes/67/rr/pdfs/rr6701-H.pdf (pages 23–24).

Last reviewed: January 17, 2025

Prior vaccine recommendations put the burden on the patient to ask for HepB vaccination if they wanted it. The recommendations published in 2022 make vaccinating adults much easier because CDC recommends that healthcare providers routinely offer HepB vaccine to ALL adult patients, including those over 60 without known risk factors. The idea of this change is to shift the burden of requesting vaccination off the patient and instead allow the provider to offer the vaccine routinely.

Last reviewed: January 17, 2025

The HepB series is now recommended for all people age 59 years and younger. Among older age groups the risk of acute hepatitis B is lower: HepB may be administered to unvaccinated adults with diabetes age 60 years and older at the discretion of the treating clinician.

In 2011, CDC first published ACIP recommendations that HepB vaccine be given to adults with diabetes because of studies showing that adults with diabetes and no other hepatitis B risk factors had twice the odds of developing acute hepatitis B compared to adults without diabetes or other risk factors. There also have been a number of outbreaks of HBV infection in settings that provide assisted blood glucose monitoring for people with diabetes.

No serologic testing or additional HepB vaccination is recommended for adults who have documentation of receiving a complete HepB series at any time in the past. For those who did not complete the vaccination series, no maximum interval between doses exists that would make the HepB vaccination series ineffective or that would require restarting the series.

Last reviewed: January 17, 2025

There is no waiting period. The varicella vaccine dose can be given at any time after the Shingrix dose. Review your procedures to prevent this from happening again. Always check the label 3 times to ensure you are administering the product intended. Such an error also should be reported to the Vaccine Adverse Event Reporting System (VAERS) by phone 1-800-822-7967 or online at https://vaers.hhs.gov.

Last reviewed: March 9, 2022

It is important to vaccinate all healthcare personnel, including paid and unpaid workers who may be exposed to patients or infectious materials. This includes direct patient care staff (e.g., physicians, nurses, and therapists), and staff and volunteers in pharmacy, radiology, laboratory, human resources, facilities management (housekeeping), food services, and laundry. Vaccination should include healthcare staff in all settings, such as hospitals, outpatient clinics, pharmacies, emergency response, nursing homes and assisted living facilities, and home care.

Last reviewed: August 11, 2024

Yes. Receipt of RhoGam is not a reason to delay vaccination. For more information see the ACIP “General Best Practice Guidelines for Immunization”, available at www.cdc.gov/vaccines/hcp/acip-recs/general-recs/timing.html.

Last reviewed: June 19, 2023

Varicella zoster immune globulin, VariZIG (Saol Therapeutics), is recommended for patients without evidence of immunity to varicella who are at high risk for severe varicella and complications, who have been exposed to varicella or herpes zoster, and for whom varicella vaccine is contraindicated. Patient groups recommended by CDC to receive VariZIG include the following:

  • Immunocompromised patients without evidence of immunity
  • Newborn infants whose mothers have signs and symptoms of varicella around the time of delivery (i.e., 5 days before to 2 days after)
  • Hospitalized preterm infants born at 28 weeks or more of gestation whose mothers do not have evidence of immunity to varicella
  • Hospitalized preterm 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
  • Pregnant people without evidence of immunity

CDC recommends administration of VariZIG as soon as possible after exposure to varicella-zoster virus, ideally within 96 hours, but not beyond 10 days after exposure. The most recent recommendations for the use of VariZIG were published in 2013 and are available at www.cdc.gov/mmwr/pdf/wk/mm6228.pdf on pages 574—576.

Last reviewed: May 16, 2023

To maximize maternal antibody response and passive antibody transfer to the infant, the optimal time to administer Tdap is between 27 and 36 weeks’ gestation, preferably during the early part of that window. However, Tdap can be administered at any time during pregnancy.

Last reviewed: March 31, 2022

CDC recommends that if a provider mistakenly administers varicella vaccine to a person for whom zoster vaccine is indicated, no specific safety concerns exist, but the dose should not be considered valid. You should administer a dose of Shingrix to the patient during that same visit (same day). If the error is not detected and corrected on the same day, Shingrix should be administered at least 8 weeks after receipt of the varicella vaccine. However, if Shingrix is inadvertently administered less than 8 weeks after the varicella vaccine, CDC experts state that the Shingrix dose does not need to be repeated if given at least 24 days after the varicella vaccine (in other words, 4 weeks minus the 4-day grace period). A second dose of Shingrix should be given 2–6 months after the first dose of Shingrix.

These events should be documented and procedures put in place, such as checking the vial label 3 times to be sure you are administering the product you intend, to prevent this from happening again.

Last reviewed: December 28, 2022

RSV vaccines are contraindicated for and should not be administered to persons with a history of severe allergic reaction, such as anaphylaxis, to any component of the vaccine. People experiencing moderate or severe acute illness with or without fever should delay RSV vaccination until they are improved, as a precaution.

Last reviewed: August 25, 2024

No. As of October 2024, CDC recommends that adults with immunocompromising conditions who received a dose of PPSV23 in the past and were previously recommended to receive a second PPSV23 dose at least 5 years after that initial PPSV23 dose should now complete their pneumococcal immunization schedule with PCV20 or PCV21 at least 5 years after the PPSV23 dose. 

Last reviewed: November 13, 2024

Yes. If time allows, use the standard Twinrix schedule of 3 doses given intramuscularly on a 0-, 1-, and 6-month schedule. If travel is imminent the accelerated 4-dose Twinrix schedule can be used: 3 doses given on days 0, 7, and 21-30 days and a booster dose at 12 months.

Last reviewed: January 27, 2025

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: January 17, 2025

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

All people working in long-term care facilities who do not have a valid contraindication should receive annual influenza vaccination.

Last reviewed: August 11, 2024

VariZIG is supplied in 125-IU vials and should be administered intramuscularly as directed by the manufacturer. The recommended dose is 125 IU/10 kg of body weight, up to a maximum of 625 IU (five vials). The minimum dose is 62.5 IU (0.5 vial) for patients weighing 2.0 kg or less and 125 IU (one vial) for patients weighing 2.1–10.0 kg. VariZIG is available from Saol Therapeutics. For ordering information see varizig.com/liquid-product_info.html.

Last reviewed: September 5, 2020

While the mother should have been given Tdap rather than Td, the Tdap dose may be given at any interval since the Td dose was given and preferably between 27 and 36 weeks’ gestation.

Last reviewed: March 31, 2022

There is no waiting period. The varicella vaccine dose can be given at any time after the RZV dose.

Last reviewed: December 28, 2022

No. There is no recommendation for a booster dose of HepA if a patient has completed the 2-dose series at any age.

Last reviewed: June 25, 2023

People with HIV infection are at increased risk for severe complications if infected with measles. It is safe to vaccinate people with HIV infection who are not severely immunosuppressed. The current criteria for safe MMR vaccination of people with HIV infection are shown below, from the CDC General Best Practices Guidelines (see the section on altered immunocompetence, www.cdc.gov/vaccines/hcp/imz-best-practices/altered-immunocompetence.html):

Two doses of MMR vaccine are recommended for all HIV-infected people age 12 months or older who do not have evidence of current severe immunosuppression (individuals age 5 years or younger must have CD4+T lymphocyte [CD4+] percentages at least 15% for at least 6 months, and individuals older than age 5 years must have CD4+ percentages at least 15% and CD4+ cell counts of at least 200 lymphocytes/mm3 for at least 6 months) and do not have current evidence of measles, rubella, and mumps immunity.

In cases when only CD4+ cell counts or only CD4+ percentages are available for those older than age 5 years, the assessment of severe immunosuppression can be based on the CD4+ values (count or percentage) that are available. In cases when CD4+ percentages are not available for those age younger than 5 years, the assessment of severe immunosuppression can be based on age-specific CD4+ counts at the time CD4+ counts were measured; i.e., absence of severe immunosuppression is defined as at least 6 months above age-specific CD4+ count criteria: CD4+count greater than 750 lymphocytes/mm3 while age 12 months or younger, and CD4+count at least 500 lymphocytes/mm3 while age 1 through 5 years. Similarly, repeat doses of MMR vaccination are recommended for individuals with perinatal HIV infection who were vaccinated before establishing effective combination antiretroviral therapy (cART). They should receive 2 appropriately spaced doses of MMR vaccine once effective cART has been established (individuals age 5 years or younger must have CD4+ percentages of at least 15% for at least 6 months; individuals older than 5 years of age must have CD4+ percentages at least 15% and CD4+ counts of at least 200 lymphocytes/mm3 for at least 6 months) unless they have other acceptable current evidence of measles, rubella, and mumps immunity.

HIV-infected people who are receiving regular doses of IGIV are unlikely to respond to varicella vaccine or MMR vaccine because of the presence of passively acquired antibody. However, because of the potential benefit, MMR and varicella vaccines should be considered approximately 14 days before the next scheduled dose of IGIV (if not otherwise contraindicated), although an optimal immune response might not occur depending on the presence of neutralizing antibodies against the vaccine virus. Vaccination should be repeated (if not otherwise contraindicated) after the recommended interval (see Table 3-6 in the Timing and Spacing of Immunobiologics of this document). In most cases, this is after the therapy has been discontinued.

Administer the first dose at 12 through 15 months and the second dose to children age 4 through 6 years, or as early as 28 days after the first dose.

Last reviewed: June 19, 2023

Both protein-based vaccines (Abrysvo, Pfizer; Arexvy, GSK) are stored in the refrigerator. RSVPreF3 (Arexvy) is supplied as a single-dose vial of lyophilized antigen component (powder) and a single-dose vial of adjuvant suspension component (liquid). Both the liquid and the powder should be stored refrigerated between 2°C and 8°C (36°F and 46°F) in the original package in order to protect vials from light. Do not freeze. Discard if either component has been frozen.

After reconstitution, administer immediately or store in the refrigerator between 2°C and 8°C (36°F to 46°F) or at room temperature (defined for this vaccine as up to 25°C [77°F]) for up to 4 hours before use. Discard reconstituted vaccine if not used within 4 hours.

Last reviewed: August 25, 2024

An asymptomatic person who is scheduled for COVID-19 vaccination and is exposed to SARS-CoV-2 virus may be vaccinated; however, COVID-19 vaccination after exposure is not recommended as post-exposure prophylaxis, so vaccination should not be expected to prevent illness caused by past exposure. A person who is currently sick with a respiratory virus should defer vaccination until at least the recovery from the acute illness, and consider additional measures to prevent spread, in accordance with current CDC guidance. Healthcare facilities may have specific policies in place to reduce the risk of spread of respiratory viruses to healthcare staff and other patients.

CDC summarizes its current guidance on respiratory viruses (updated March 2024) here: http://www.cdc.gov/respiratory-viruses/guidance/index.html.

People who recently had SARS-CoV-2 infection and are due for a COVID-19 vaccine may consider delaying the dose by up to 3 months from symptom onset or positive test (if infection was asymptomatic). According to CDC, increasing the time between infection and vaccination may result in an improved immune response to vaccination. At this time, there is evidence of a low risk of reinfection in the weeks following infection. A recipient’s individual risks for severe disease and current COVID-19 conditions in the community should be taken into account when deciding whether to delay vaccination up to 3 months after infection.

Last reviewed: November 16, 2024

In October 2024, CDC updated its guidance to state that an adult who received PCV13 should receive PCV20 or PCV21at least 1 year later. PPSV23 is no longer recommended as an option following PCV13.

Last reviewed: November 13, 2024

Both protein-based RSV vaccines (Abrysvo, Pfizer; Arexvy, GSK) are stored in the refrigerator. RSVpreF (Abrysvo) is supplied in a kit that includes a vial of lyophilized antigen component (a white powder), a prefilled syringe with a sterile water diluent, and a vial adapter. Store at refrigerated temperatures between 2°C and 8°C (36°F and 46°F) in the original carton. Do not freeze. Discard if frozen. Follow reconstitution guidelines at www.fda.gov/media/168889/download.

After reconstitution, administer immediately or store at room temperature (defined for this vaccine as 15ºC to 30ºC [59°F to 86°F]) for up to 4 hours. Do not store reconstituted Abrysvo vaccine in the refrigerator or freezer. Discard reconstituted vaccine if not used within 4 hours.

Last reviewed: August 25, 2024

The mRNA RSV vaccine (mResvia, Moderna) is supplied as a manufacturer-filled syringe (MFS) that contains a frozen suspension that must be thawed before administration either in the refrigerator or at room temperature. Vaccine should not be refrozen once thawed. Do not shake any mRNA vaccine because shaking can damage the potency of the vaccine by breaking up the small bubbles of fat (lipid) that contain the mRNA.

  • Freezer storage: The frozen vaccine in the plastic MFS can be stored in the freezer between -40°C to -15°C (-40°F to 5°F) until the expiration date printed on its packaging.
  • Refrigerator storage: The thawed plastic MFS may be stored refrigerated between 2°C to 8°C (36°F to 46°F) for up to 30 days before being used. If stored in the refrigerator, place a label on the vaccine indicating when it was placed in the refrigerator and its ‘use by date’, which is 30 days later. Discard an MFS that has been in the refrigerator beyond its 30-day use-by date.
  • Room temperature storage: The thawed plastic MFS may be stored between 8°C to 25°C (46°F to 77°F) for a total of 24 hours after removal from refrigerated conditions. Discard the MFS if not used within this time. Do not return an MFS to the refrigerator after it has been thawed at room temperature.
  • Refer to the mResvia package insert for specific instructions and additional details on storage and thawing: www.fda.gov/media/179005/download.
Last reviewed: August 25, 2024

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: January 17, 2025

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

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: August 11, 2024

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

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

Nirsevimab (Beyfortus, Sanofi) 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: August 25, 2024

ACIP and CDC do not recommend revaccination with a second dose of PPSV23 for adults 19 through 49 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 administration of a dose of PCV20 or PCV21 at least 5 years after the dose of PPSV23.

Last reviewed: November 13, 2024

Yes, COVID-19 vaccines and other routine immunizations, including influenza and RSV vaccines and nirsevimab (RSV preventive antibody for infants), 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 about simultaneous administration with other vaccines is available from CDC: www.cdc.gov/vaccines/covid-19/clinical-considerations/interim-considerations-us.html#age-transitions.

Last reviewed: November 16, 2024

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

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

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.