NEJM: Study of the effectiveness of mRNA-1273 in children aged 6 months to 5 years

As of July 2022, more than 13.
6 million cases of COVID-19 have been reported in children in the United States, with most of them having no symptoms or only mild symptoms, but the threat of community transmission
remains.
Despite social interventions to reduce Covid-19 transmission, Covid-19-related hospitalizations and deaths among children under 5 years of age in the United States from October 2020 to September 2021 still exceeded those caused by influenza in the pre-pandemic year
.
The mRNA-1273 vaccine is safe and effective in preventing SARS-CoV-2 infection in adults, adolescents, and children aged 6-11 years, and although it is less effective in preventing Omicron variant infection, it is still very effective
in preventing hospitalization and death from Omicron infection.
Researchers have evaluated the effectiveness
of the mRNA-1273 vaccine in children aged 6 months to 5 years.

The study was divided into 2 phases, one was a phase II-III dose study and the other was a single-dose placebo-controlled evaluation
.
According to the conclusions of the first phase of the study, in the second phase, children aged 6 months to 5 years received two doses of 25 μg of mRNA-1273 or placebo 28 days
apart.
The primary objective was to assess the safety and reactogenicity of the vaccine and to compare the immune
response in children with those of young people aged 18-25 years.
The secondary endpoint was to assess the risk of
infection after mRNA-1273 inoculation.

A total of 3040 children aged 2-5 years and 1762 children aged 6-23 months received two 25 μg mRNA-1273 injections; 1008 children aged 2 to 5 years and 593 children aged 6-23 months received placebo
.
The median follow-up after the second injection was 71 days in the 2- to 5-year-old cohort and 68 days
in the 6- to 23-month cohort.
Most of the adverse events were minor and transient, and no new safety issues
were found.
At day 57, the geometric mean concentration of neutralizing antibodies in the 2-5 year age population was 1410 and 1781 in children aged 6-23 months, compared with 1391 in other populations receiving 100 μg of mRNA-1273 injection, reaching the endpoint of non-inferiority of immune response.

During the B.
1.
1.
529 (Omicron) epidemic, the efficacy of mRNA-1273 vaccine in children aged 2-5 years and children aged 6-23 months was 36.
8% and 50.
6%,
respectively.

Two doses of 25 μg mRNA-1273 vaccine were considered safe for children aged 6 months to 5 years, and the immune response after vaccination was comparable
to that of other groups.

Original source:

Evan J.
Anderson et al.
Evaluation of mRNA-1273 Vaccine in Children 6 Months to 5 Years of Age，N Engl J Med，October 20, 2022.