COVID-19 Vaccines: Reassuring Safety Data / 1 Shot If You've Had COVID?

By Amy Orciari Herman

Edited by David G. Fairchild, MD, MPH

A CDC analysis of adverse event data during the first month of COVID-19 vaccination in the U.S. offers reassurance on use of the two authorized mRNA vaccines. The findings appear in MMWR.

Between Dec. 14, 2020, and Jan. 13, 2021, nearly 14,000,000 vaccine doses were given, and roughly 7000 adverse events were reported to the U.S. Vaccine Adverse Event Reporting System. Of these, 91% were considered nonserious. Headache, fatigue, and dizziness were most common.

The overall rate of anaphylaxis was 4.5 per million doses — which, the researchers note, is "within the range" of rates seen with other common vaccines.

Overall, 113 deaths occurred after vaccination, most in residents of long-term-care facilities. The researchers report that "causes of death were consistent with background all-cause mortality and did not indicate any unexpected pattern that might suggest a causal relationship with vaccination."

Among Pfizer-BioNTech vaccine recipients enrolled in the CDC's "v-safe" program — a smartphone-based tool that allows automated health check-ins after COVID-19 vaccination — reactions were more common after the second dose than after the first. (Information on second doses of the Moderna vaccine were not yet available.)

The researchers conclude, "These initial findings should provide reassurance to health care providers and to vaccine recipients and promote confidence in the safety of COVID-19 vaccines."

In other vaccine news, a New York Times story rounds up several recent studies — not yet peer-reviewed — suggesting that one dose of COVID-19 vaccine may be sufficient for people who've already been infected with SARS-CoV-2. For example, in one small study, the first dose of the Pfizer-BioNTech vaccine conferred up to a thousandfold increase in antibody levels in people who'd had COVID-19 months earlier, whereas the second dose did little beyond that. In contrast, people who had not been infected previously had robust antibody responses to both doses. Meanwhile, in another study among previously infected individuals, a single dose of either the Pfizer-BioNTech or Moderna vaccine elicited high levels of neutralizing antibodies against B.1.351, the more transmissible variant first detected in South Africa. The Times story notes that it's unknown how long such antibody responses will last.