Two half doses of Moderna's coronavirus vaccine spurred infection-fighting antibodies in children aged 6 to 11 years old and resulted in side effects similar to those reported in adolescents and adults, the company announced Monday, outlining plans to ask the Food and Drug Administration for an expanded emergency authorization.
The initial results in this age group come from the broader KidCOVE trial that Moderna is running in partnership with the National Institutes for Health. The study is enrolling children as young as 6 months old and testing a smaller dose of the two-shot regimen for safety and immune response.
The trial hasn't accrued enough data yet to measure whether the vaccine prevents infections or symptomatic disease in younger children. But the results disclosed Monday indicate the immune responses raised a month after the two-shot regimen are high enough to be likely to prevent COVID-19, based on previous testing in teenagers and adults.
Moderna said side effects were mostly mild, such as injection site pain and fatigue. Trial researchers and regulators will be watching longer-term safety data closely, though, as more serious side effects including a type of heart inflammation called myocarditis have been linked to Moderna's vaccine in rare cases.
Authorization of vaccines for younger children could open a new front in the coronavirus pandemic response as public health officials attempt to extend vaccination coverage. While children and adolescents seem less vulnerable to complications and death from COVID-19 than older adults, immunizing them against infection could help limit community spread and lower the risk of outbreaks that can close schools and workplaces.
And as the delta variant swept across the U.S. this summer, cases of COVID-19 were largely concentrated in unvaccinated people, which meant children made up a larger share of those who got infected and sick.
Pfizer and BioNTech have already reported detailed results for their vaccine in children between the ages of 5 and 11. The shot's use in kids will be reviewed by expert FDA advisers Tuesday and could gain an emergency use authorization from the regulator soon after.
So far, the Pfizer-BioNTech vaccine is the only one available for use in people under age 18, with those 12 and older currently permitted to receive the full dose of its two-shot regimen.
Moderna's data released Monday is from an analysis of 4,753 children who received two shots containing 50 micrograms of the messenger RNA-based vaccine and had been followed for one month afterwards for safety and immune responses. The trial will continue following the children for up to a year to measure whether they were less likely to become infected or sick than those who were given placebo.
In total, the trial has enrolled 5,700 children, and researchers will do separate analyses on those aged 2 to 5 years and those aged 6 months to 2 years.
Measured by prevention of COVID-19, Pfizer's vaccine has set a benchmark of about 91% efficacy when using a dose one-third the size of the adult shot. That data appears to have convinced FDA scientists, who estimated the vaccine's benefit in preventing disease and death outweigh its risks, particularly myocarditis. While a rare occurrence, myocarditis has been observed more frequently in younger men.
In addition to reviewing vaccines in children, the FDA has recently assessed booster shots in adults who received their primary series earlier this year. So far, the agency has given a green light to additional shots of full-dose Pfizer and Johnson & Johnson vaccines, a half dose of the Moderna vaccine, and a "mix-and-match" boosting scheme that permits people to get a different shot than their initial series.
The FDA has put some limits on who receives boosters, however. Only older people and those at high risk of infection who got Pfizer or Moderna primary dose can receive an additional dose, while those who initially got J&J's vaccine can get a booster because of that shot's relatively lower efficacy.