Nearly all local and systemic adverse events (AEs) reported after Pfizer or Moderna’s COVID-19 vaccines were mild and transient, and only a fraction of individuals reported seeking medical care, according to data from the Vaccine Adverse Event Reporting System (VAERS) and CDC’s v-safe tracker.
Out of almost 300 million mRNA vaccine doses administered in the U.S. from Dec. 14, 2020 to June 14, 2021, 92% of self-reported AEs to VAERS were not serious, and under 1% of individuals reporting data to v-safe said they sought medical care for their AEs after dose one and dose two, reported Julianne Gee, MPH, of the CDC in Atlanta, and colleagues, writing in Lancet Infectious Diseases.
Interestingly, they found that females and individuals ages 65 and younger reported more reactogenicity following vaccination than males and older adults. The authors noted that “a greater proportion of vaccines was administered to females… males” at 53.2% versus 45.8% in the study time period. Also, the median age at vaccination was 50 for those who got the Pfizer vaccine and 56 for those who got the Moderna vaccine. They advised that on the basis of these findings, “mild-to-moderate transient reactogenicity should be anticipated, particularly among younger and female vaccine recipients.”
“COVID-19 vaccine safety monitoring is the most robust in U.S. history and the two complementary surveillance systems used in this study should bolster confidence that mRNA COVID-19 vaccines are safe,” said co-author Hannah Rosenblum, MD, also of the CDC, in a statement.
The authors examined self-reported data from both VAERS and v-safe on 298,792,852 individuals in the U.S. who received Pfizer or Moderna vaccines. Of the 340,522 reports to VAERS, 92% were non-serious, 6.6% were serious (non-death), and 1.3% were deaths.
However, Gee’s group noted caveats to the deaths, namely that reporting on any deaths after vaccination was required since the products were under emergency use authorization, but no unusual patterns were detected in the cause of death reports. They added that 80% of deaths were among adults ages 60 and up. They also pointed out that a different surveillance system demonstrated no increased risk of non-COVID-19 mortality in vaccinated people.
“The rapid pace at which COVID-19 vaccines were administered under emergency use, especially among older populations, was unprecedented,” said co-author David Shay, MD, also of the CDC, in a statement. “Due to their age, this group already has a higher baseline mortality rate than the general population and our results follow similar patterns of death rates for people in this age group following other adult vaccinations.”
The most common systemic AE reported to VAERS for both vaccines was headache (20%), followed by fatigue (17%) and fever (16%). Among the serious AEs reported, shortness of breath was the most common (15%) for both vaccines.
The CDC v-safe system tracked AEs after both dose one and two, and found that of the almost 8 million v-safe participants, about 70% reported systemic AEs after dose two versus only 53% after dose one. Headache and fatigue were the most commonly reported systemic AEs, with 56% reporting headache and 46% reporting fatigue after dose two.
Examining local AEs, about two-thirds of participants reported injection site pain after both vaccine doses.
In an accompanying editorial, Matthew Krantz, MD, and Elizabeth Phillips, MD, both of Vanderbilt University School of Medicine in Nashville, Tennessee, characterized the report as “reassuring,” noting that, “there were no unexpected signals other than myopericarditis and anaphylaxis, already known to be associated with mRNA vaccines.”
“The predictable, nonserious, and transient nature of the adverse events provides an objective basis for employees to be given provision for paid time off work to increase vaccine confidence and uptake by individuals,” they wrote.
Krantz and Phillips added that v-safe data may be underreported in socioeconomically disadvantaged populations who might not have access to the web-based survey system.
Other limitations noted by Gee’s group included potential underreporting to VAERS; that death certificate and autopsy reports were only available for a minority of deaths; and most importantly, “VAERS data alone generally cannot establish causal relationships between vaccination and adverse events,” they said.
The study was supported by the CDC.
Gee and co-authors disclosed no relationships with industry.
Krantz disclosed no relationships with industry. Phillips disclosed support from UpToDate, Janssen, Vertex, BioCryst, and Regeneron, as well as being co-director of IIID, which holds a patent for HLA-B*57:01 testing for abacavir hypersensitivity, and has a patent pending for Detection of Human Leukocyte Antigen-A*32:01 in connection with Diagnosing Drug Reaction with Eosinophilia and Systemic Symptoms.