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Moderna's COVID vaccine (Spikevax) was safe, effective, and produced an immune response in children ages 6-11, an interim analysis of a phase II/III trial found.

Two 50 μg doses of vaccine -- half the dose of Moderna's primary series for adults -- administered 28 days apart produced a non-inferior immune response in children ages 6-11 as in adults ages 18-25, reported Sabine Schnyder Ghamloush, MD, of Moderna in Cambridge, Massachusetts, and colleagues.

In a modified intention-to-treat population, estimated vaccine efficacy (VE) was 88.0% (95% CI 70.0-95.8) against symptomatic COVID (primarily the Delta variant) at 14 days or more following the first injection, the authors wrote in the .

The manufacturer first in October 2021, although no efficacy results were reported at that time. More recently, Moderna announced it would be filing for emergency use authorization (EUA) for this vaccine and its vaccine for children 6 months to 5 years of age (two 25 μg doses).

Ghamloush's group shared the results of the , which took place in the U.S. and Canada, and was comprised of three age cohorts: 6-11 years, 2-5 years, and 6 months to 23 months. Part 1 was a dose selection study where 751 children received either two 50 μg or 100 μg doses of the vaccine, and the manufacturer selected the 50 μg dose moving forward.

In part 2, children were assigned 3:1 to receive either two injections of vaccine or placebo. VE was based on incidence of COVID infection among all participants without serologic or virologic evidence of SARS-CoV-2 injection at baseline, and who received at least one injection. Symptomatic COVID was defined as a positive PCR test plus one systemic or respiratory symptom.

From March to August 2021, 4,016 participants were enrolled in part 2 of the trial. Overall, 2,998 participants in the vaccine group and 973 participants in the placebo group received two injections. Mean age of participants in the safety cohort was about 9 years, 51% were boys, and two-thirds were white. About 20% had obesity.

Similar to the adult trials, solicited systemic adverse events (AEs) after the second dose were higher in the vaccine group than in the placebo group (78% vs 50%, respectively). The most common AEs were headache and fatigue, though chills and fever were higher following the second injection compared with the first in the vaccine group. The majority of AEs were grade 1 or 2, but there was a higher proportion of grade 3 AEs in the vaccine group than in the placebo group (12% vs 1%).

Serious AEs in the vaccine group included appendicitis, cellulitis, and orbital cellulitis, but were considered to be unrelated to the vaccine, the authors said. There were no cases of anaphylaxis, multi-system inflammatory syndrome in children (MIS-C), myocarditis, or pericarditis attributable to the vaccine or placebo as of the cut-off date, the researchers wrote.

Ghamloush's team added that at least 99% of both children and young adults had serologic responses a month following the second injection, which met the non-inferiority success criterion.

There were seven COVID cases in the vaccine group and 18 cases in the placebo group at least 14 days after the first injection. Estimated VE against SARS-CoV-2 infection was 74.0% (95% CI 57.9-84.1), regardless of symptoms, and estimated VE against asymptomatic infection specifically was 62.5% (95% CI 30.9-79.4).

The investigators added that the populations were too small and the time period too short to calculate VE after two injections in the per-protocol population.

Given that the trial occurred during the Delta wave, the authors concluded that the "findings suggest that this vaccine provides a protective benefit for children against variants of concern."

The trial is ongoing in both this population and younger children, the team noted.

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