Top 5 Takeaways

  1. Reduction in Adverse Reactions: Among adults aged ≥50 years, adverse reactions were less frequent following a second mRNA COVID-19 booster dose compared to the first booster dose.
  2. High Volume of Second Booster Doses: Approximately 16.8 million persons aged ≥50 years in the U.S. received a fourth dose of a COVID-19 vaccine during the study period.
  3. Majority Nonserious Events: Of 8,515 adverse events reported to VAERS, 95% were nonserious, indicating a favorable safety profile for the second booster dose.
  4. V-safe and VAERS Surveillance Systems: The safety monitoring relied on data from the v-safe active surveillance system and the VAERS passive surveillance system, highlighting their importance in post-vaccination safety assessments.
  5. ACIP Recommendations: The Advisory Committee on Immunization Practices (ACIP) continues to recommend booster doses for enhanced protection against COVID-19, with specific guidelines for adults aged ≥50 years and immunocompromised persons.

Original Article Author and Citation

Corresponding Author

Anne M. Hause,

Suggested Citation

Hause AM, Baggs J, Marquez P, et al. Safety Monitoring of COVID-19 mRNA Vaccine Second Booster Doses Among Adults Aged ≥50 Years — United States, March 29, 2022–July 10, 2022. MMWR Morb Mortal Wkly Rep 2022;71:971–976. DOI:


The CDC reviewed safety data for the second mRNA COVID-19 booster doses among adults aged ≥50 years, reporting fewer adverse reactions compared to the first booster dose. Data from v-safe and VAERS between March 29 and July 10, 2022, indicated a high safety profile with 95% nonserious events among 8,515 reports.


The study analyzed adverse events reported to the v-safe and VAERS systems following the administration of second mRNA booster doses. V-safe is an active surveillance system, while VAERS is a passive system. Analysis focused on the frequency and severity of reported adverse events.


The findings reinforce the safety of the second booster doses in adults aged ≥50 years, with fewer adverse reactions reported than after the first booster. The importance of continuous safety monitoring through v-safe and VAERS is emphasized, contributing to ongoing vaccine safety assessments and recommendations.


The study’s findings support the continued administration of second booster doses to eligible populations, with ACIP’s recommendations highlighting the importance of boosters for sustaining protection against COVID-19. The low frequency of serious adverse events underscores the vaccines’ safety profile.

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