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.
There is a rare risk of myocarditis (inflammation of the heart muscle) and/or pericarditis (inflammation of the tissue surrounding the heart) following receipt of any COVID-19 vaccine. This rare risk is greatest in biological males age 12 through 39 years. Despite this risk, evaluation conducted in past seasons demonstrated that the benefits of vaccination clearly outweigh the risks in all age groups. SARS-CoV-2 virus infection poses a substantially higher risk of myocarditis or pericarditis than COVID-19 vaccination.
The risk after vaccination appears related to age (12 through 39 years), biological sex (male), and the short (3- to 4-week) interval between initial series doses. For the 2025–2026 formulations, an initial series is no longer recommended except in infants and toddlers younger than age 2 years or in people with moderate or severe immunocompromise. These groups have not historically been associated with an increased risk of pericarditis or myocarditis following COVID-19 vaccination. Extending the interval between doses to 8 weeks in infants and toddlers may reduce the rare risk of myocarditis following the second dose; however, this is not recommended if delaying vaccination poses an unacceptable risk of severe COVID-19 illness.
Most patients diagnosed with myocarditis after mRNA COVID-19 vaccination have been hospitalized for short periods, with most completely recovering from their acute symptoms. Post-vaccination myocarditis is milder than myocarditis following viral infection. CDC continues to assess long-term outcomes in people with myocarditis after mRNA COVID-19 vaccination.
People who receive COVID-19 vaccines, especially males age 12 through 39, should be counseled about the risk of myocarditis or pericarditis and advised to seek medical attention promptly if they develop chest pain, shortness of breath, or feelings of a fast, fluttering, or pounding heartbeat.
Cases of myocarditis and pericarditis were identified in clinical trials of the adjuvanted protein subunit COVID-19 vaccine (now with brand-name Nuvaxovid) and have also been reported during post-authorization use outside the United States.
CDC’s complete interim clinical considerations for COVID-19 vaccination and myocarditis or pericarditis are available here: www.cdc.gov/covid/hcp/vaccine-considerations/safety-considerations.html#cdc_vaccine_special_topics_research-covid-19-vaccination-and-myocarditis-and-pericarditis.
CDC also has published additional clinical considerations for the evaluation and care of patients with myocarditis or pericarditis following mRNA vaccination: https://www.cdc.gov/vaccines/covid-19/clinical-considerations/myocarditis.html (CDC Archive).
Yes. Pneumococcal vaccines are all inactivated vaccines, which means you can give all other recommended vaccines at the same visit (using separate syringes) or at any later time with no waiting period following the vaccination. All currently available meningococcal vaccines in the United States may be administered without regard to the timing of pneumococcal vaccination.
No. Only the number of doses indicated in the manufacturer’s package insert should be withdrawn from the vial. For a 5.0 mL vial of Fluzone this is 10 doses. For Afluria 5.0 mL multidose vial, the package insert states that the stopper can be punctured up to 20 times, allowing up to 20 doses of 0.25 mL dose for children age 6–35 months old. After the maximum number of doses has been withdrawn or number of punctures of the stopper has met the FDA-recommended limit, the vial should be discarded, even if there is vaccine remaining in the vial and the expiration date has not been reached.
This issue will be uncommon in 2025–26 because of the ACIP vote in 2025 to recommend use of single-dose influenza vaccine formulations for people of all ages. Availability of multidose vials in 2025–26 varies by manufacturer.
Serious allergic reactions, such as anaphylaxis, in the minutes following vaccination are rare but are possible with any vaccine. Every vaccination site should have staff available who are trained and equipped to recognize and respond to signs of anaphylaxis in a vaccine recipient. See this CDC website for additional information about preparing for the management of anaphylaxis following COVID-19 vaccination: www.cdc.gov/vaccines/covid-19/clinical-considerations/managing-anaphylaxis.html?anaphylaxis-management.html.
Anaphylaxis following vaccination with mRNA COVID-19 vaccines is reported at a rate of approximately 5 cases per million doses administered.
An immediate severe allergic reaction to any component or previous dose of any mRNA COVID-19 vaccine is a contraindication to vaccination with all mRNA COVID-19 vaccine formulations; however, such a reaction is generally a precaution (not a contraindication) to the use of the adjuvanted protein subunit vaccine (Nuvaxovid, Sanofi-Novavax). The CDC’s COVID-19 interim clinical considerations section on contraindications and precautions for details: www.cdc.gov/covid/hcp/vaccine-considerations/contraindications-precautions.html#cdc_vaccine_special_topics_research-considerations-for-people-with-a-history-of-allergies-or-allergic-reactions.
Children age 7–10 years should receive Tdap if they are not fully vaccinated for prevention of pertussis. Otherwise they may receive Td or Tdap. If additional doses are necessary for full tetanus protection, they may be administered as Td or Tdap. Adolescents, and adults age 11 years and older should receive a single dose of Tdap, if they have not received a dose of Tdap after the 11th birthday, otherwise they may receive Td or Tdap. If additional doses are necessary for full tetanus protection, they may be administered as Td or Tdap.
Anti-HBs testing for HCP who receive both hepatitis B immune globulin (HBIG) and hepatitis B vaccine can be conducted as soon as 6 months after receipt of the HBIG.
No. The available data have been interpreted that any changes in antibody response to either vaccine’s components were clinically insignificant. If PCV20 and influenza vaccine are both indicated and recommended, they may be administered at the same visit.
The dose does not need to be repeated. However, this is a vaccine administration error. Clinicians should carefully select an influenza vaccine and vaccine dose that is licensed for the age group of the person being vaccinated. The error should be conveyed to the child’s parent or guardian and reported to Vaccine Adverse Events Reporting System (VAERS) at www.vaers.hhs.gov. Actions should be taken to limit vaccine administration errors at the clinic where the error occurred. Immunize.org’s educational piece “Influenza Vaccine Products for the 2025-2026 Influenza Season” (available at www.immunize.org/catg.d/p4072.pdf) provides helpful information on the wide variety of influenza vaccines in use this season.
In accordance with general best practices for vaccination, all people should be observed for at least 15 minutes after vaccination for signs of an immediate allergic reaction.
If you vaccinate a person who has an allergy-related precaution to COVID-19 vaccination with the same type of COVID-19 vaccine associated with the precaution, you should consider a 30-minute observation period following vaccination. See CDC’s detailed considerations for people with a history of allergies or allergic reactions: www.cdc.gov/covid/hcp/vaccine-considerations/contraindications-precautions.html#cdc_vaccine_special_topics_research-considerations-for-people-with-a-history-of-allergies-or-allergic-reactions.
ACIP has not addressed this issue specifically. Puncture wounds, however, should be attended to as soon as possible. The decision to delay a booster dose of tetanus toxoid-containing vaccine following an injury should be based on the nature of the injury and likelihood that the injured person is susceptible to tetanus. The more likely the person is to be susceptible, the more quickly that tetanus prophylaxis should be administered. A person with a tetanus-prone wound (e.g., punctures, wounds contaminated with soil or fecal material) and who has no history of tetanus immunization must be vaccinated and given tetanus immune globulin (TIG) as soon as possible. A person with a documented series of at least three tetanus toxoid-containing products, with a booster dose within the previous 10 years ago is less likely to be susceptible to tetanus, and the need for a booster dose is not as urgent, particularly if the wound can be thoroughly cleaned. The more likely a person is to be completely susceptible to tetanus (i.e., unvaccinated or incompletely vaccinated), the sooner that TIG and Td/Tdap should be administered, even if it means a trip to the emergency department.
No. HCP with written documentation of receipt of a complete, properly spaced HepB series AND a positive anti-HBs can be considered immune to HBV and require no further testing or vaccination. Testing unvaccinated or incompletely vaccinated HCP (including those without written documentation of vaccination) is not necessary and is potentially misleading because anti-HBs of 10 mIU/mL or higher as a correlate of vaccine-induced protection has only been determined for persons who have completed a HepB vaccination series. Persons who cannot provide written documentation of a complete HepB vaccination series should complete the series, then be tested for anti-HBs 1 to 2 months after the final dose.
RIV is not licensed for people younger than 9 years of age, so there are no data regarding safety and efficacy in this age group. However, no serious side effects would be expected. The dose does not need to be repeated and should be considered valid. Even if no adverse reaction occurs, vaccine administration errors like this should be reported to the Vaccine Adverse Events Reporting System (VAERS) at www.vaers.hhs.gov.
Pneumococcal vaccination recommendations are complex, especially as newer conjugate vaccines are licensed and added to recommended options. Assessing what is needed for an individual patient of any age requires their age, pneumococcal vaccination history, and knowledge of any relevant high-risk conditions. There are several resources available from CDC and Immunize.org that can help:
CDC Resources:
Immunize.org Resources:
No. There are no data on the effectiveness of pneumococcal conjugate vaccine given by the intravenous route. The patient has renal disease, so it is important to ensure that the dose they receive is effective. CDC recommends repeating the dose using the correct route of administration (intramuscular).
One dose of tetanus toxoid-containing vaccine (Tdap or Td) provides little or no protection. That is why tetanus immune globulin (TIG) is also recommended in this situation. See the Tetanus Prophylaxis for Wound Management section of the current ACIP statement, available at www.cdc.gov/mmwr/volumes/67/rr/pdfs/rr6702a1-H.pdf, pages 27–28. As far as timing, the toxoid and TIG should be given as soon as possible.
No. HCP who have documentation of receiving a complete HepB series and who tested positive for anti-HBs (defined as anti-HBs of 10 mIU/mL or higher) are considered to be immune to hepatitis B. Immunocompetent persons have long-term protection against HBV and do not need further testing or vaccine doses. Some immunodeficient persons (including those on hemodialysis) may need periodic booster doses of hepatitis B vaccine.
TIG is recommended for any wound other than a clean minor wound if the person’s vaccination history is either unknown, or the person has not had a full series of 3 doses of tetanus-containing vaccine. People with HIV infection or severe immunodeficiency who have contaminated wounds (including minor wounds) should also receive TIG, regardless of their history of tetanus immunizations. TIG should be given as soon as possible after the injury. The dose is 250 IU administered intramuscularly. See CDC’s web page for details: www.cdc.gov/tetanus/hcp/clinical-guidance/index.html.
For all licensed COVID-19 vaccines (Moderna [mNexspike, Spikevax], Sanofi-Novavax [Nuvaxovid], Pfizer-BioNTech [Comirnaty]) healthcare providers are strongly encouraged to report to the Vaccine Adverse Event Reporting System (VAERS) the following:
Information on how to submit a report to VAERS is available at https://vaers.hhs.gov or by calling 1-800-822-7967.
PPSV23 may be administered by intramuscular (IM) or subcutaneous (Subcut) routes. Pneumococcal conjugate vaccines are administered IM. Immunize.org has produced a simple handout that summarizes the dose, route, site, and needle length for administration of all recommended vaccines to adults and children: www.immunize.org/catg.d/p3085.pdf.
No. The series should not be restarted. Continue the series from where you left off.
All pneumococcal vaccines should be refrigerated at temperatures between 2°C (36°F) and 8°C (46°F). Do not freeze these vaccines. Vaccine exposed to freezing temperature should not be administered. For details of vaccine storage and handling, see the CDC Vaccine Storage and Handling Toolkit: www.cdc.gov/vaccines/hcp/downloads/storage-handling-toolkit.pdf.
If the error is discovered on the same clinic day you can administer the other “half” of the FluLaval dose on the same day. If the error cannot be corrected on the same day, the partial dose should not be counted. The child should be recalled to the office as soon as possible and given a full age-appropriate repeat dose, either a 0.5 mL dose of FluLaval, a 0.5 mL dose of Fluarix, a 0.25 or 0.5 mL dose of Fluzone, a 0.25 mL dose of Afluria, or a 0.5 mL dose of Flucelvax.
Multiple national surveillance systems are used to monitor the safety of COVID-19 vaccines in different ways. CDC provides information about vaccine safety surveillance systems, with links to information about the safety of COVID-19 vaccines, here: www.cdc.gov/vaccine-safety/vaccines/covid-19.html.
The incubation period of tetanus ranges from 3 to 21 days, averaging about 10 days. In general, the further the injury site is from the central nervous system, the longer the incubation period. In the opinion of the tetanus experts at the CDC, for a person who has been vaccinated but is not up to date, there is probably little benefit in giving TIG more than a week or so after the injury. For a person believed to be completely unvaccinated, it is suggested to increase this interval to 3 weeks (i.e., up to day 21 post injury). Td or Tdap should be given concurrently with TIG.
Because there is no documentation of vaccination, a vaccination series should be administered and postvaccination testing should be performed 1–2 months after the final dose of vaccine. There is no harm in receiving extra doses of vaccine. Postvaccination anti-HBs testing results should also be documented, including the date testing was performed. All healthcare settings should develop policies or guidelines to assure valid hepatitis B immunization.
V-safe is a safety monitoring system that vaccine recipients can use to share with CDC how they feel after vaccination. It was created initially for COVID-19 vaccines. Currently, recipients of RSV vaccines also may register for V-safe. To learn more about the program and how to guide vaccine recipients who wish to participate, visit CDC’s website: www.cdc.gov/vaccine-safety-systems/v-safe/index.html.
Each of these products must be stored at 2° to 8°C (36° to 46°F). They should not be frozen or exposed to freezing temperatures.
All influenza vaccines (inactivated, recombinant, and live attenuated vaccines) should be stored at refrigerator temperature of 2° through 8°C (36° through 46°F). No influenza vaccine should be frozen. Influenza vaccine exposed to freezing temperature should not be used.
No. A positive anti-HBs indicates that the vaccinated person is immune at the time the person was tested but does not assure that the person has long-term immunity. Long-term immunity has been demonstrated only for people attaining an adequate anti-HBs result of at least 10 mIU/mL after completing a full vaccination series. The most direct way to deal with this is to vaccinate the employee with a series of hepatitis B vaccine; test for anti-HBs in 1–2 months and document the result in the employee’s health record. An adequate anti-HBs result from a documented vaccine series would assure not only seroprotection, but long-term protection.
No. COVID-19 vaccines are not currently part of the VICP, although a transition to the VICP is anticipated in the future. The COVID-19 vaccines are currently part of a similar program called the Countermeasures Injury Compensation Program (CICP). For more information, visit this web page: www.hrsa.gov/cicp.
Do nothing. Data show that vaccine-induced anti-HBs levels might decline over time; however, immune memory (anamnestic anti-HBs response) remains intact following immunization. People with anti-HBs concentrations that decline to less than 10 mIU/mL are still protected against HBV infection. For healthcare professionals with normal immune status who have demonstrated adequate anti-HBs (at least 10 mIU/ mL) following full vaccination, booster doses of vaccine or periodic anti-HBs testing are not recommended.
No. There are no regulations that require removal from job situations where exposure to bloodborne pathogens could occur; this is an individual policy decision within the organization. OSHA regulations require that employees in jobs where there is a reasonable risk of exposure to blood be offered HepB vaccine. In addition, the regulation states that adequate personal protective equipment be provided and that standard precautions be followed. Check your state OSHA regulations regarding additional requirements. If there are no state OSHA regulations, federal OSHA regulations should be followed. Adequate documentation should be placed in the employee record regarding non-response to vaccination. HCP who do not respond to vaccination should be tested for HBsAg and total anti-HBc to determine if they have chronic HBV infection. If the HBsAg and total anti-HBc tests are positive, HCP should receive appropriate counseling for preventing transmission to others as well as referral for ongoing care to a specialist experienced in the medical management of chronic HBV infection. People who are HBsAg-positive and who perform exposure-prone procedures should seek counsel from a review panel comprised of experts with a balanced perspective (for example, infectious disease specialists and their personal physician[s]) regarding the procedures that they can perform safely. They should not be excluded from work. People who test negative for HBsAg should be considered susceptible to HBV infection and should be counseled about precautions to prevent HBV infection and the need to obtain HBIG prophylaxis for any known or likely exposure to HBsAg-positive blood (see Table).
For details, refer to the specific vaccine’s package insert.
Immunize.org has assembled links to key COVID-19 vaccine resources, including package inserts, in the Checklist of Current Versions of U.S. COVID-19 Vaccination Guidance and Clinic Support Tools: www.immunize.org/catg.d/p3130.pdf.
Although routine transportation of vaccines to different facilities is not generally recommended, there are times when this is necessary. CDC recommends transporting COVID-19 vaccine in unopened vials or manufacturer-filled syringes (MFS) and always with a continuous temperature monitoring device to ensure adherence to authorized storage times and temperatures. See the product package insert for details on permissible conditions for transport.
Yes. HCP should not be discriminated against because of their hepatitis B status. All HCP should practice standard precautions, which are designed to prevent HBV transmission, both from patients to HCP and from HCP to patient. There is, however, one caveat concerning HBV-infected HCP. Those who have HBV levels 1000 IU/mL or 5000 genomic equivalents/mL or higher should not perform exposure-prone procedures (for example, gynecologic, cardiothoracic surgery) unless they have sought counsel from an expert review panel and been advised under what circumstances, if any, they may continue to perform these procedures. For more information on this issue, see “Updated CDC Recommendations for the Management of Hepatitis B Virus–Infected Health-Care Providers and Students,” MMWR, 2012; 61(RR03):1–12. This document is available at www.cdc.gov/mmwr/pdf/rr/rr6103.pdf.
Yes. HepB vaccines have been demonstrated to be safe when administered to infants, children, adolescents, and adults. Since 1982, well over 100 million people, including infants, children, and adults living in the United States have received at least one dose of HepB vaccine; more than a billion doses of HepB vaccine have been given worldwide. Vaccination causes a sore arm occasionally, but serious reactions are very rare.
Many years of experience with Engerix-B and Recombivax HB vaccines and recent studies of Heplisav-B indicate no apparent risk for adverse events to a developing fetus. Current vaccines contain noninfectious HBsAg and pose no risk to the fetus. If the mother is being vaccinated because of a risk factor for HBV infection (for example, a healthcare worker, a person with a sexually transmitted disease, an injection drug user, a person with multiple sex partners), vaccination should be initiated as soon as the risk factor is identified during the pregnancy. HBV infection during pregnancy might result in severe disease for the mother and chronic infection for the newborn.
Any of the available HepB vaccines (Engerix-B, Heplisav-B, Recombivax HB) or the HepA-HepB combination vaccine, Twinrix, may be used during pregnancy.
No. Administration of HepB soon after birth has not been associated with an increased rate of elevated temperatures or subsequent evaluations for possible sepsis in the first 21 days of life.
A serious allergic reaction to a prior dose of HepB or a vaccine component is a contraindication to further doses of HepB. Engerix-B, Recombivax HB, Twinrix, and Heplisav-B are synthesized in yeast cells into which a plasmid containing the gene for HBsAg has been inserted. People with a severe allergic reaction to yeast should not be vaccinated with vaccines produced in yeast cells.
As with other vaccines, vaccination of people with moderate or severe acute illness, with or without fever, should be deferred until the illness improves. Vaccination is not contraindicated in people with a history of multiple sclerosis, Guillain-Barré syndrome, or autoimmune diseases such as systemic lupus erythematosus or rheumatoid arthritis.
All hepatitis B-containing vaccines should be stored at refrigerator temperature at 2°C to 8°C (36°F to 46°F). The vaccines must not be frozen. Any vaccine exposed to freezing temperature should not be used. Do not use these or any other vaccines after the expiration date shown on the packaging. Any vaccine administered after its expiration date should be repeated.
