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Safety Monitoring Updates (March 1, 2021)

At the March 1, 2021 meeting of the Centers for Disease Control and Prevention (CDC) Advisory Committee on Immunization Practices (ACIP), Dr. Tom Shimabukuro, a member of the CDC COVID-19 Vaccine Task Force, provided a safety update on the COVID-19 vaccines from Pfizer-BioNTech and Moderna. This safety update was based on information reported to CDC by both health care providers and people who had received one or two doses of the vaccines as of February 16, 2021. By this date, 55.2 million vaccine doses had been administered in the U.S. Overall, the safety profile of COVID-19 vaccines continues to be reassuring and consistent with safety data observed from the pre-authorization clinical trials. In addition, no unexpected pregnancy or infant outcomes have been observed related to COVID-19 vaccination during pregnancy.

CDC has a comprehensive COVID-10 vaccine safety monitoring system in place to conduct post-marketing surveillance of COVID-19 vaccines following the issuance of emergency use authorizations (EUAs). The EUAs for the Pfizer-BioNTech and Moderna vaccines were issued on December 11 and 18, 2020, respectively. The presentation at the ACIP meeting on March 1st reported on vaccine safety data from several monitoring programs including v-safe, the Vaccine Adverse Event Reporting System (VAERS), and the Vaccine Safety Datalink (VSD) platform as noted below. Additional information about ongoing efforts to ensure COVID-19 vaccine safety can be found on websites maintained by CDC and FDA.

V-safe is a smartphone based “after vaccination health checker” where people who have received a COVID-19 vaccine can quickly tell CDC about any side effects they experienced. An analysis of safety data collected by the v-safe program during the first month of administration of the Pfizer-BioNTech and Moderna vaccines (December 14 – January 13) was published on February 19th in CDC Morbidity and Mortality Weekly Report (MMWR). Side effects (such as injection site pain, headache, fatigue, and muscle soreness) were similar for both the Pfizer-BioNTech and Moderna vaccines and consistent with those reported in the Phase 3 clinical trials.

The Vaccine Adverse Event Reporting System (VAERS) accepts reports from everyone regardless of the whether the vaccine caused the side effect or the level of clinical seriousness of the event. However, VAERS can rapidly detect safety “signals” and rare adverse events that warrant further investigation. Among the 105,000 COVID-19 vaccine-related adverse effects reported to VAERS as of February 16th, 94% were non-serious and 6% were serious (similar to experience with influenza vaccines). The most common side effects reported were headache, fatigue, fever, dizziness, chills, and pain at injection site, with no new safety concerns noted. Anaphylaxis continues to be a rare occurrence, with an estimated 2.5 cases per million doses administered for the Moderna vaccine, and 4.7 cases per million doses administered for the Pfizer-BioNTech vaccine as reported in the Journal of the American Medical Association .

CDC also utilizes Vaccine Safety Datalink (VSD), a collaborative project with nine health care organizations across the country to monitor possible adverse events when new vaccines are licensed (or authorized for emergency use such as for the current COVID-19 vaccines). Notably, CDC can assess if the rate of adverse events among vaccinated people is higher than among a comparison unvaccinated group; a higher rate of specific adverse events in vaccinated people may represent a “safety signal” that needs further attention. As of February 13, 2021, no such safety signals were detected among people vaccinated with either the Pfizer-BioNTech or Moderna vaccines as compared to the unvaccinated population.

More than 30,000 pregnant women who received either the Pfizer-BioNTech or Moderna COVID-19 vaccines have registered in the v-safe program. The side effect profile and adverse events observed among pregnant women did not indicate any safety issues, and most reports to the VAERS system among pregnant women involved non-pregnancy-specific side effects (local or systemic effects like injection-site pain, headache, fatigue, and muscle soreness). Pregnancy-specific adverse events such as miscarriage were within the known background rates for unvaccinated women.