Top 5 Takeaways

  1. Decreased adverse reactions after second booster: Among individuals ≥50 years who received homologous mRNA COVID-19 vaccination, both injection site and systemic reactions were reported less frequently after a second booster dose compared to after the first booster dose.
  2. High percentage of nonserious events reported to VAERS: The Vaccine Adverse Event Reporting System (VAERS) received 8,515 reports of adverse events following second mRNA booster doses (of 286,380 people with second doses reporting overall), with 94.8% being nonserious.
  3. Healthcare providers and patients advised on vaccine reactions: It is recommended that healthcare providers inform patients that local and systemic reactions are expected post-second booster, though serious adverse events are rare.
  4. High participation in homologous vaccination: Among v-safe registrants, 86.9% received vaccines from the same manufacturer for all four doses, indicating a high rate of homologous vaccination.
  5. V-safe and VAERS data indicate safety: Preliminary safety findings from v-safe and VAERS suggest that second booster doses are associated with fewer adverse reactions compared to the first booster and primary series doses.

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:


This article reports on the safety monitoring of second mRNA COVID-19 booster doses among adults aged ≥50 years in the United States from March 29, 2022, to July 10, 2022. Analysis of data from v-safe and VAERS indicated that adverse reactions were less frequent after a second booster dose compared to the first booster dose. The majority of reported events were nonserious.


The CDC reviewed adverse events and health impact assessments reported to v-safe and VAERS following receipt of second mRNA booster doses. The review included analysis of reports from approximately 286,380  individuals aged ≥50 years who received a fourth dose of a COVID-19 vaccine.


The findings indicate that local and systemic reactions post-second booster are expected and align with previous observations. The data also demonstrate a decrease in adverse reaction frequency compared to earlier doses, reinforcing the safety profile of mRNA COVID-19 vaccines.


The safety monitoring data for second booster doses among adults aged ≥50 years suggest that these doses are associated with fewer and less severe adverse reactions compared to previous doses. Health care providers and patients should be aware of the expected reactions, with serious adverse events remaining uncommon.

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