How the risk of side effects could change with Covid-19 vaccine boosters

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.