Pfizer and Moderna are expanding the size of their vaccine trials for children 5 to 11 years old, seeking to better detect very rare heart issues among those vaccinated.
The major vaccine makers are increasing the number of children enrolled in their studies at the prompting of the federal Food and Drug Administration, first reported by The New York Times.
The FDA asked the companies to include 3,000 children — or double the previous number of participants — in order to be adequately able to detect rare side effects such as myocarditis or pericarditis, inflammations of the heart, according to unnamed sources who spoke to the Times.
The side effect is very unlikely, showing up in only 12.6 cases per 1 million second doses, according to the U.S. Centers for Disease Control and Prevention (CDC). Last month, the FDA updated its vaccine fact sheets to include the possible increased risk.
Coronavirus cases are on the rise across the country as the highly contagious delta variant spreads, with cases and deaths overwhelmingly among people who are unvaccinated.
The Pfizer-BioNTech vaccine has already been authorized for children 12 and older, and the Moderna vaccine is authorized for those 18 and older.
As schools are set to reopen for in-person learning in the fall, the issue of vaccinating students is top of mind for parents, teachers and school staff.
Pfizer, which started vaccine trials in children 11 and younger in March, said on its website that it expects to have study results to submit to the FDA for emergency use authorization for 5- to 11-year-olds in September or October. A Pfizer spokesperson told HuffPost that the company has not provided any further updates to its vaccine trial timelines for children.
Moderna, which also started vaccine trials in children younger than 12 in March, expects to seek emergency authorization in late 2021 or early 2022, a spokesperson told the Times.