Pfizer and Moderna are expanding their vaccination trials to 5 to 11-year-olds
They expect to seek emergency authorisation for the age group later this year.
Pfizer and Moderna are expanding the size of their vaccine trials to now include children from 5 to 11 years old.
At the request of the US Food and Drug Administration (FDA), the vaccine makers are increasing the number of children in their trials in order to better detect very rare heart issues among those vaccinated against Covid-19, the New York Times reports.
Unnamed sources say the FDA asked the companies to include 3,000 children in the trials to detect rare, inflammatory side effects on the heart such as myocarditis or pericarditis.
Such side effects are reportedly very unlikely, showing up in just 12.6 cases per 1 million second doses, according to the US Centres for Disease Control and Prevention (CDC).
Pfizer started vaccine trials in children 11 and younger back in March.
Its website now states that it expects to have trial results to submit to the FDA for emergency authorisation for 5 to 11-year-olds in September or October.
The Pfizer-BioNTech vaccine has already been authorised by the FDA for children aged 12 and above.
A spokesperson told the Times that Moderna, which also started vaccine trials in children younger than 12 in March, expects to seek emergency authorisation for the age group in late 2021 or early 2022.
Earlier this month, director of the FDA's Centre for Biologics Evaluation and Research Peter Marks wrote in a letter to the editor of the Times that the Covid-19 vaccines authorised in the US have been "thoroughly evaluated," meeting the FDA's "rigorous standards."