Are the Covid mRNA Vaccines Safe?

A new scientific study entitled Serious adverse events of special interest following mRNA vaccination in randomized trialsprovides the best evidence yet concerning the safety of the mRNA Covid vaccines. For most vaccines in common use, benefits far outweigh risks, but that may not be the case for the mRNA covid vaccines, according to this study by Joseph Fraiman and his colleagues. It depends on your age and medical history.

The randomized controlled clinical trial is the gold standard of scientific evidence. When regulators approved the Pfizer and Moderna mRNA vaccines for emergency use in December 2020, two randomized trials showed that the vaccines reduced symptomatic covid infection by over 90% during the first few months after the second dose.

Pfizer and Moderna did not design the trials to evaluate long-term efficacy or the more important outcomes of preventing hospitalization, death, or transmission.

The randomized trials did collect adverse event data, including the presence of mild symptoms (such as fever) and more serious events requiring hospitalization or leading to death. Most vaccines generate some mild adverse reactions in some people, and there were considerably more adverse such reactions after the mRNA vaccines compared to the placebo.

That is annoying but not a major issue. We care about severe health outcomes. The key question is whether the vaccine’s efficacy outweighs the risks of severe adverse reactions.

The Fraiman study uses data from the same Pfizer and Moderna-sponsored randomized trials presented to the FDA for vaccine approval, but with two innovations that provide additional information.

First, the study pools data from both mRNA vaccines to increase the sample size, which decreases the confidence intervals’ size and the uncertainty about the estimated harms.