CHICAGO • Moderna's Covid-19 vaccine was shown to be effective in adolescents aged 12 to 17 and showed no new or major safety problems in a clinical trial, the developer said yesterday, potentially setting the stage for a second vaccine for school-age children to be authorised in July.

Moderna, whose vaccine is authorised for adults aged 18 and older, said it will submit the findings of its adolescent study to the US Food and Drug Administration and other regulators for emergency use authorisation early next month.

US regulators took about a month to review a similar study from Pfizer-BioNTech, which was authorised for ages 12 to 15 on May 10. If Moderna gets the same treatment, its authorisation would come in early July. Widely vaccinating 12-to 18-year-olds could allow US schools and summer camps to relax masking and social distancing measures suggested by the US Centres for Disease Control and Prevention (CDC).

"We are encouraged that mRNA-1273 was highly effective at preventing Covid-19 in adolescents," Moderna's chief executive Stephane Bancel said in a statement.

Moderna's trial evaluated the vaccine in 3,732 adolescents aged 12 to 17, two-thirds of whom got the vaccine and one-third of whom got a placebo. The main goal was to produce an immune response on a par with that seen in the company's large, phase three trial in adults, which was 94.1 per cent effective at preventing Covid-19.

Two weeks after the second dose, researchers found no cases of Covid-19 in the vaccine group compared to four cases in the placebo group, resulting in a vaccine efficacy of 100 per cent, based on case definitions from the company's adult trial.

The researchers found no new safety issues. The most common side effects after the second dose were headaches, fatigue, body aches and chills.

The company said it is still accumulating safety data. All study participants will be monitored for 12 months after their second dose to determine long-term protection and safety.

REUTERS