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Ask the Experts: COVID-19: Vaccine Safety

Results (12)

Recipients of mRNA COVID-19 vaccines often experience local (e.g., pain, swelling, redness at the injection site, localized swollen lymph nodes in the armpit of the vaccinated arm) or systemic (e.g., fever, fatigue, headache, chills, body and joint aches) post-vaccination symptoms. Depending on vaccine product (Pfizer-BioNTech vs. Moderna), age group, and vaccine dose, in clinical trials, approximately 80–91% of vaccinated people develop at least one local symptom and 55–91% develop at least one systemic symptom following vaccination.

Most systemic post-vaccination symptoms are mild to moderate in severity, occur within the first three days of vaccination, and resolve within 1–3 days of onset.

Among children ages 6 months through 4 years (Pfizer-BioNTech) or 6 months through 5 years (Moderna), pain or tenderness at the injection site was the most frequent local reaction. The most common systemic symptom in older children was fatigue; in younger children (ages 6 through 23 months), irritability/crying and drowsiness/sleepiness were most common. Most systemic symptoms were mild to moderate in severity, typically began 1 to 2 days after vaccination, and resolved after 1 to 2 days.

Last reviewed: October 26, 2023

In clinical trials of Novavax COVID-19 Vaccine, pain or tenderness at the injection site was the most frequently reported local reaction among vaccine recipients; redness and swelling were reported less frequently. Fatigue, headache, and muscle pain were the most commonly reported systemic reactions. Most symptoms were mild to moderate in severity and resolved within 1 to 3 days. Overall, symptoms were more frequent in people ages 18 through 64 years compared to people ages 65 years and older and more frequent after dose 2 than dose 1.

Last reviewed: October 26, 2023

Vaccine safety monitoring in the United States indicated an increased risk of GBS within 42 days of vaccination with the Janssen COVID-19 Vaccine, with the highest risk among people ages 40 through 64. Most reports were in males. Janssen COVID-19 Vaccine is no longer available in the United States.

Any FDA-authorized or FDA-licensed updated (2023–2024 Formula) COVID-19 vaccine may be given to individuals with a history of GBS.

Last reviewed: October 26, 2023

There is no evidence that any of the COVID-19 vaccines affect current or future fertility.

Last reviewed: October 26, 2023

A rare risk for myocarditis (inflammation of the heart muscle) and/or pericarditis (inflammation of the tissue surrounding the heart) has been observed following receipt of mRNA COVID-19 vaccines and Novavax COVID-19 Vaccine. Despite this observation, evaluation demonstrates that the benefits of vaccination clearly outweigh the risks in all age groups.

Among mRNA vaccine recipients, these rare cases of myocarditis or pericarditis have occurred most frequently in adolescent and young adult males within the first week after receiving the second dose of an mRNA COVID-19 vaccine primary series. Myocarditis is even more rare in children younger than age 12 years after COVID-19 vaccination. This risk appears related to age, biological sex, and the short (3- to 4-week) interval between primary series doses. Extending the interval to 8 weeks for some people for whom a vaccination series is recommended may reduce the rare risk of myocarditis following the second dose.

Most patients diagnosed with myocarditis after mRNA COVID-19 vaccination have been hospitalized for short periods, with most completely recovering from their acute symptoms. CDC is assessing long-term outcomes in people with myocarditis after mRNA COVID-19 vaccination.

People receiving 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 Novavax COVID-19 Vaccine and have also been reported during post-authorization use outside the United States. These findings suggest that an increased risk for these conditions may be present after receiving Novavax COVID-19 vaccine.

Current recommendations are for a single dose of any FDA-licensed or FDA-authorized updated (2023–2024 Formula) COVID-19 vaccine for most people age 5 years and older, even if the individual is previously unvaccinated. Previously unvaccinated individuals who receive Novavax vaccine are recommended to receive two doses, given three to 8 weeks apart.

CDC’s complete interim clinical considerations for COVID-19 vaccination and myocarditis or pericarditis are available here:

CDC also has published additional clinical considerations for the evaluation and care of patients with myocarditis or pericarditis following mRNA vaccination:

Last reviewed: October 26, 2023

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:

Anaphylaxis following vaccination with mRNA COVID-19 vaccines is reported at a rate of approximately 2 to 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 both the Pfizer-BioNTech and Moderna vaccines (all formulations); however, such a reaction is generally a precaution to the use of the Novavax vaccine; see the CDC’s COVID-19 interim clinical considerations section on contraindications and precautions for details:

CDC also provides specific COVID-19 vaccination guidance for people with a history of allergies or allergic reactions:

Last reviewed: October 26, 2023

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 a precaution to COVID-19 vaccination, 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:

Last reviewed: October 26, 2023

Visit this CDC website for information for the public concerning allergic reactions and COVID-19 vaccines:

For information about how to evaluate and manage people with a history of allergy who present for COVID-19 vaccination, see CDC’s additional considerations for people with a history of allergies or allergic reactions:

Last reviewed: October 26, 2023

Adverse events that occur in a recipient following COVID-19 vaccination should be reported to VAERS. Vaccination providers are required by FDA to report the following that occur after COVID-19 vaccination:

  • Vaccine administration errors whether or not associated with an adverse event
  • Serious adverse events, irrespective of attribution to vaccination
  • Cases of Multisystem Inflammatory Syndrome (MIS) in adults and children
  • Cases of myocarditis after a Pfizer-BioNTech or a Moderna vaccine
  • Cases of pericarditis after a Pfizer-BioNTech or a Moderna vaccine
  • Cases of COVID-19 that result in hospitalization or death

Reporting is encouraged for any other clinically significant adverse event, even if it is uncertain whether the vaccine caused the event. Information on how to submit a report to VAERS is available at or by calling 1-800-822-7967.

Last reviewed: October 26, 2023

Multiple national surveillance systems are used to monitor the safety of COVID-19 vaccines in different ways. Please see this CDC website for additional information on how they help ensure the safety of COVID-19 vaccines in the United States:

Last reviewed: October 26, 2023

CDC’s v-safe program for COVID-19 vaccination, a voluntary smartphone-based tool that used text messaging and web surveys for personalized health check-ins after a COVID-19 vaccination, provided timely information about COVID-19 vaccine safety. The program closed enrollment on May 19, 2023.

Last reviewed: October 26, 2023

No. The 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:

Last reviewed: October 26, 2023

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