Study of 6.2 million Americans show no significant side effects from COVID-19 RNA vaccines
The new study adds to a growing volume of data indicating that the RNA-based COVID-19 vaccines in population-wide use are safe.
8 September 2021 – by Priya Joi
What is the research about?
One of the biggest concerns in rolling out COVID-19 vaccines is to ensure that real-world safety matches what scientists have seen in their clinical trials. While no vaccine is rolled out if there is doubt about its safety, post-trial studies of vaccination are critical to ensure that no side effects emerge when the pool of vaccinated people expands into the millions. Studies such as these are intended to monitor and look for signals of potential side effects.
This study adds to the growing body of real-world evidence that COVID-19 vaccines are safe for use in the general population, and that the benefits of the vaccine far outweigh the risks of possible side effects.
What did the researchers do?
Researchers in the US have analysed data from the Vaccine Safety Datalink, a collaboration between different health plans and the US Centers for Disease Control and Prevention (CDC). They reviewed health issues faced by 6.2 million people who had been given at least one dose of Pfizer-BioNTech or Moderna mRNA vaccines (5.7 million of these had been given two doses). Participants were 54% female and had an average age of 49 years.
The researchers looked for any condition that could be or had been associated with COVID-19 vaccines, including neurological disorders such as encephalitis and myelitis, seizures, and Guillain-Barré syndrome; cardiovascular problems such as acute myocardial infarction, stroke, and pulmonary embolism as well as and Bell’s palsy, appendicitis, anaphylaxis, and multisystem inflammatory syndrome. They looked at health events recorded between mid-December 2020 to the end of June, 2021, comparing health events 1 - 21 days post-vaccination compared with 22 - 42 days post-vaccination to see whether they were likely to be attributable to vaccination.
What did they find?
The researchers found no significant associations between vaccination with mRNA COVID-19 vaccines and any of the health outcomes 1 - 21 days and 22 – 42 days after vaccination. Myocarditis has been a side effect of concern, and in this study they found 34 cases of myocarditis or heart inflammation out of the 6.2 million people included in the study, clustered in younger patients aged 12 to 39 years old; 85% of them were male. Of these younger patients, there was a risk of 6.3 additional myocarditis cases per million doses during the first week after vaccination, although nearly all recovered. Phase 3 trials for both mRNA vaccines had noted that the incidence of Bell's palsy was higher in those vaccinated than in the placebo group. In this study, there was no evidence of an association between Bell's palsy and mRNA vaccines, a finding the researchers say "is consistent with a recent analysis of cases reported to the World Health Organization database.”
What does this mean?
This study adds to the growing body of real-world evidence that COVID-19 vaccines are safe for use in the general population, and that the benefits of the vaccine far outweigh the risks of possible side effects. With more than 5 billion vaccine doses administered globally, even the rarest adverse events can be easily identified and investigated in time to ensure the ongoing safety of people who have been vaccinated.