Additional doses of Covid-19 vaccines are likely rolling out in the United States later this year. It raises the question: What will the side effects from a booster shot look like? Is there a higher or lower risk of an adverse event, compared to the earlier regimens?
Overall, the Covid-19 vaccines are overwhelmingly safe and remarkably effective. But as the shots went into millions of arms starting late last year, researchers uncovered a handful of sometimes serious side effects, which were so exceedingly rare that the clinical trials that led to the shots’ authorizations — even with tens of thousands of participants — couldn’t capture them. Researchers don’t fully understand the root causes of some of the side effects, but they’ve also reported that the risk of some of them, including certain heart and blood clotting issues, is much higher after a Covid-19 infection itself than after receiving a Covid-19 vaccine.