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First Month of COVID-19 Vaccine Safety Monitoring – United States, December 14, 2020-January 13, 2021

Our take —

In the first month of vaccination against SARS-CoV-2 in the US, over 13 million doses of the Pfizer-BioNTech and Moderna vaccines were administered, and about 7,000 (0.05%) adverse events were reported to a nationwide surveillance network. Over 90% of these were non-serious reactions, of which headache, fatigue, and dizziness were the most common. There were 62 anaphylactic reactions, the proportion of which (0.0004%) is similar to that found with other commonly administered vaccines. Although 113 deaths were reported to the surveillance system, there were no indications that any of these were related to vaccination itself.

Study design


Study population and setting

This was a descriptive analysis of safety data for the Pfizer-BioNTech and Moderna SARS-CoV-2 vaccines during the first month of vaccination in the United States, from December 14, 2020 to January 13, 2021. Data were reported to the Vaccine Adverse Event Reporting System (VAERS), a national passive surveillance system with follow-up for serious adverse events, and to v-safe, an active safety monitoring system into which patients self-enroll. Serious adverse events reported to VAERS were followed up to obtain medical records, additional health care information, and death certificates and autopsy reports in the case of death. V-safe enrollees are sent links to online surveys via text message, and provide information related to local and systemic vaccine reactions, as well as whether they missed work, could not perform normal activities, or sought medical care (those who seek medical care are contacted by v-safe). Participants are asked about their pregnancy status and pregnancies are followed up through a registry.

Summary of Main Findings

During the first month of vaccination, 13,794,904 vaccine doses were administered. The median age of recipients was 42 years, and 61% were women. During this period, VAERS received 6,994 (0.05%) reports of adverse events. Of these, 6,354 (91%) were classified as non-serious, and 640 (9%) were classified as serious, including 113 deaths (78 of which were among residents of long-term care facilities). For 38 deaths, half of which occurred among residents in long-term care facilities, record review was ongoing at time of publication; for all other deaths, underlying conditions were listed as the primary cause, and there were no causal links seen between vaccination and mortality. There were 62 confirmed cases of anaphylaxis. Headache (22% of those with any adverse event), fatigue (17%), and dizziness (17%) were the most commonly reported symptoms. V-safe respondents who reported adverse events most commonly reported pain at the injection site, fatigue, headache, myalgia, and chills; reactions were most commonly reported the day after vaccination. Reported reactions occurred at similar frequencies with the Pfizer-BioNTech and Moderna vaccines. 10,825 respondents (0.68%) reported being pregnant at the time of vaccination.

Study Strengths

VAERS is a pre-existing national surveillance network with follow-up for serious adverse events. Supplementing results with those from v-safe reinforced findings regarding the most commonly reported events.


Because VAERS is a passive surveillance network, underreporting of events is possible due to lack of compliance with reporting requirements. Alternatively, it is possible that the attention and sensitivity surrounding COVID-19 vaccine rollout lowered the threshold for reportable events below that established for other vaccines such as that for seasonal influenza. V-safe relies on self-enrollment and is thus subject to selection effects that limit generalizability of results in unpredictable ways. The total number of vaccines administered was not reported for important strata in VAERS results (e.g., Moderna vs. Pfizer-BioNTech, dose 1 vs. dose 2), limiting comparisons of the incidence of adverse events. Investigations of 38/113 deaths were incomplete at time of publication.

Value added

This is the first comprehensive report of adverse events associated with SARS-CoV-2 vaccination in the United States outside of clinical trials.

This review was posted on: 12 March 2021