Moderna doses adolescents in COVID-19 vaccine study, setting it up to target 2021-22 school year

Moderna manufacturing site
Moderna may infer efficacy through immunobridging to the adult population. (Moderna)

Moderna has dosed the first adolescents in a phase 2/3 clinical trial designed to position its COVID-19 vaccine for use in children as young as 12 years old before the start of the 2021-22 school year.

Having shown mRNA vaccine mRNA-1273 is safe and effective in adults, Moderna is now running a 3,000-subject trial in adolescents. Moderna is aiming to deliver data in adolescents in the spring of 2021, setting it up to get an expanded label in time for a vaccination campaign ahead of the next school year.

“By the time we go back in September 2021, the kids can go back to school with a normal school year, which is so important to know in terms of equality and then kids’ development and education and mental health and so on. That's our plan for adolescents,” Moderna CEO Stéphane Bancel said at a recent investor event.

COVID-19 outcomes in adolescents are typically better than in adults, with the severity of disease roughly correlating with age. However, children have been negatively affected by school closures, particularly in the U.S. where states have been accused of prioritizing businesses over K-12 when it comes to making decisions about what to shut to control the coronavirus. Countries in Europe have typically prioritized keeping schools open.

Moderna wants to help states keep schools open next year—and access an additional population—by running a clinical trial that will randomize adolescents to receive either the 100-μg vaccine dose used in the adult phase 3 or placebo. Like adults, adolescents will receive two doses 28 days apart.  

The size of the trial and rate of symptomatic COVID-19 in adolescents means Moderna is unlikely to be able to show its vaccine prevents disease by the spring. However, if a correlate of protection is found, Moderna could use that to infer efficacy. Alternatively, the biotech will infer efficacy through immunobridging to the adult population. Safety and reactogenicity are the primary endpoints. 

COVID-19 vaccine trials have so far mainly enrolled adults aged 18 years and older. Pfizer amended its phase 2/3 protocol to support enrollment of younger people partway through the trial and sent the FDA reactogenicity data on 100 adolescents aged 12 to 15 years in its filing for emergency use authorization. However, Pfizer is not currently seeking EUA in children as young as 12 years as it has too few data to support a favorable benefit-risk determination. 

Pfizer is seeking authorization in adolescents aged 16 and 17 years, though, despite lacking solicited reactogenicity data as of the cutoff for the EUA. Reactions were detected and reported as unsolicited adverse events. The EUA safety population includes data on 283 people aged 16 or 17 years.

Having administered its vaccine to hundreds of adolescents, Pfizer is ahead of Moderna in the race for that part of the market. But the potential for the back-to-school period to see surging demand for vaccines authorized for use in adolescents suggests Pfizer’s lead may not translate into a meaningful advantage.