- The Food and Drug Administration needs more time to review Moderna's request to clear its coronavirus shot for use in adolescents and teenagers so the agency can better assess the risk of a type of heart inflammation seen in rare cases after vaccination.
- The extra time will help the FDA evaluate "recent international analyses" of the risk of myocarditis and the agency may not finish that review until January, Moderna said. Moderna won't file for authorization in young children until the FDA completes its assessment, a delay from previous plans.
- The announcement comes just days the FDA authorized Pfizer and BioNTech's similar, rival shot for kids as young as 5, concluding the benefits of vaccination far outweigh any risk of myocarditis. Pfizer could have the only COVID-19 vaccine authorized for use in U.S. teenagers and children for several months.
Moderna's and Pfizer's vaccines are based on the same messenger RNA technology and had near-identical results in clinical testing, strong findings that set up initial U.S. authorizations within weeks of one another. Both have since become the most widely used shots in the country, accounting for more than 95% of the doses administered in the U.S. since distribution began late last year.
While there are many similarities between the two shots, some differences have emerged, too.
Some real-world studies, for instance, have shown Moderna's shot boosts the levels of virus-fighting antibodies higher than Pfizer's and may provide slightly better protection against infection and disease — a finding that could be due to the higher doses in Moderna's two-shot regimen.
But some countries have reported a higher rate of myocarditis among recipients of Moderna's shot — particularly among younger people — which has led several European nations to pause its use in people 30 and under. (Myocarditis is also associated with COVID-19, and the form associated with vaccination is usually mild.)
The latter finding has caught the attention of regulators in the U.S., who have already flagged myocarditis as a top concern when evaluating mRNA shots in children. Before authorizing Pfizer's shot in 5- to 11-year-olds, the FDA rigorously analyzed the risk of myocarditis and put together a series of statistical models comparing it to the potential benefits of vaccination in a variety of scenarios. Nearly all of those scenarios significantly favored vaccination, leading staff scientists to support use Pfizer's vaccine, which was cleared for children on Friday. The FDA authorized Pfizer's shot for 12- to 15-year-olds in May.
Moderna, whose shot is only available to U.S. adults, had been aiming to closely follow Pfizer. But it will now have to wait for a few more months, leaving Pfizer's shot to dominate the early rollout of COVID-19 vaccines in younger Americans.
In a statement over the weekend, Moderna said the FDA wants more time to review international datasets on myocarditis risk. That review will delay authorization of the vaccine in 12- to 17-year-olds, as well as Moderna's planned filing in children as young as 6. Moderna, for its part, noted that more than 1.5 million adolescents have received its shot and its global safety database "does not suggest an increased risk of myocarditis" in that age group. But the company also doesn't have access to "some recent international analyses," which it didn't specify.
Myocarditis rates with Pfizer's shot appear to be most common among 16- to 29-year-olds but less frequent in younger adolescents. Pfizer believes those rates will be lower in children, who are receiving a much smaller dose than teenagers and adults.
Moderna is using a similar strategy. Though it seeks to use the same dose in 12- to 17-year-olds as adults, the dose being studied in children is half the size. Moderna said just last week that two shots of that dose were safe and spurred a strong immune response in a clinical trial in 6- to 11-year-olds. Results in younger children are expected later this year or early next.