Pioneering research has unveiled that COVID vaccine side effects are predominantly mild and start to decline rapidly one day following vaccination.
An extensive study in the United States has provided comprehensive insights into the immediate impacts of mRNA vaccines, suggesting that COVID vaccine side effects decreased significantly shortly after injection and did not elicit severe adverse events.
The research indicates that of the 298 million vaccine doses administered between December 2020 and June 2021, 92% of adverse events were not serious and less than 1% of v-safe participants required medical attention following vaccination.
The study is published in The Lancet Infectious Diseases.
VAERS and v-safe
At the height of the pandemic, two mRNA vaccines were approved for emergency use in the US – Pfizer-BioNTech (BNT162b2) and Moderna (mRNA-1723). The vaccines required two primary doses and displayed good safety profiles in clinical trials. The most common reported COVID vaccine side effects were pain at the injection site, fatigue, and headaches.
In the US, individuals can report side effects from any vaccines using the Vaccine Adverse Event Reporting System (VAERS), which is jointly run by the US Centers for Disease Control and Prevention (CDC) and the US Food and Drug Administration (FDA). VAERS can be utilised by US residents, their healthcare providers, or vaccine manufacturers to submit any event experienced following an inoculation.
VAERS reports are classified as non-serious, serious, or death. Additionally, the v-safe system, managed by the CDC, was created specifically for the COVID vaccination programme and is comprised of smartphone surveys sent each day for the first week following vaccination and at longer intervals for the months following to assess COVID vaccine side effects.
Dr Hannah Rosenblum, of the US Centers for Disease Control and Prevention (CDC), commented: “Vaccines are the most effective tool to prevent serious COVID-19 disease outcomes and the benefits of immunisation in preventing serious illness and death strongly favour vaccination. COVID-19 vaccine safety monitoring is the most robust in US history and the two complementary surveillance systems used in this study should bolster confidence that mRNA COVID-19 vaccines are safe.”
The extent of COVID vaccine side effects
The researchers’ study examined available VAERS and v-safe self-reported data between December 2020 and June 2021 following two doses of either Pfizer-BioNTech or Moderna mRNA vaccines. 235 million doses of mRNA vaccines were administered during this time – 132 million Moderna and 167 million Pfizer.
VAERS had over 340,000 reports of COVID vaccine side effects, with 92% registered as non-serious, including headache (20%), fatigue (17%), fever (16%), and pain (15%). Of the 6.6% of side effects registered as serious, the most common was shortness of breath (15%. Of all the adverse events, 4500 (1.3%) were deaths, with over 80% of these being among people aged 60 and over.
The v-safe system included eight million participants, with 4.6 million reporting local and 3.6 reporting systemic reactions post-vaccination, which occurred more frequently after dose two than dose one. COVID vaccine side effects were primarily mild, with the most common being fatigue, 34% after the first dose and 56% after the second. 27% and 46% reported headaches after the first and second dose, respectively, with 66% documenting injection site pain after the first dose and 69% after dose two.
The team found that more v-safe participants were unable to work, perform daily activities, or needed medical care after dose two than dose one – 32% compared to 12%. Moreover, less than 1% reported seeking medical attention after either vaccine dose.
Dr Tom Shimabukuro, the study’s author from the CDC, said: “VAERS and v-safe are important tools CDC can use when evaluating vaccine safety and to help identify any unexpected or unusual events. These data are reassuring that reactions to both mRNA vaccines are generally mild and subside after one or two days—confirming reports from clinical trials and post-authorisation monitoring.”
Study limitations
The authors noted that a limitation of their investigation is that VAERS relies on spontaneous reporting and is not representative of the entire population, meaning it cannot establish a causal relationship between vaccination and adverse events. Additionally, the requirement of smartphone access to use v-safe excludes people without these devices. Furthermore, VAERS and v-safe cannot distinguish the safety differences between the Pfizer-BioNTech and Moderna mRNA vaccines despite there being trends in adverse reactions.
Elizabeth Phillips, Vanderbilt University Medical Center USA, who was not involved in the study, said: “Reassuringly, the six-month VAERS data supports that, although approximately one in 1,000 individuals vaccinated may have an adverse effect, most of these are non-serious. No unusual patterns emerged in the cause of death or serious adverse effects among VAERS reports… For adverse events of special interest, it is reassuring that there were no unexpected signals other than myopericarditis and anaphylaxis, already known to be associated with mRNA vaccines.”
