Two doses of Moderna vaccine effective against SARS-CoV-2 infection and hospitalization in children aged 6 months to 5 years

A CITF-funded study, published in preprint and not yet peer-reviewed, found that a 2^nd dose of the Moderna vaccine was associated with reduced symptomatic SARS-CoV-2 infection (vaccine effectiveness [VE]=90%), as well as reduced COVID-19-related hospitalization (VE=82%) in children aged 6 months to 5 years. This study was led by Dr. Jeffrey Kwong (University of Toronto and ICES) in collaboration with Drs. Jonathon Maguire and Catherine Birken (both Unity Health Toronto).

This retrospective, test-negative study that used linked administrative data in Ontario included 572 test-positive cases and 3467 test-negative controls for the period from July 28, 2022, to December 31, 2022. Of the 572 children who tested positive for SARS-CoV-2 (showing a positive RT-PCR test result), 27 (4.7%) were vaccinated. Of the 3,467 who tested negative (via RT-PCR), 240 (6.9%) were vaccinated.

Key findings:

• Overall, VE against symptomatic SARS-CoV-2 infection was 20% ≥14 days following a first dose and 90% ≥7 days following a second dose.
• 222 children were hospitalized for COVID-19 related reasons, but fewer than 10 of those had received a Moderna vaccine. VE against COVID-19-related hospitalization was 58% ≥14 days after a first dose and 82% ≥7 days after a second dose.
• Test-positive cases were more likely to be under a year old. They were also more likely to live in areas with higher household density.
• Age or a previously documented SARS-CoV-2 infection did not affect VE against symptomatic SARS-CoV-2 infection.

The study included community-dwelling children between the ages of six months and 5 years old as of July 28, 2022. The children underwent testing for SARS-CoV-2 by real-time polymerase chain reaction (RT-PCR) and had documented signs or symptoms consistent with SARS-CoV-2 infection. The study excluded children who were immunocompromised, those without provincial health insurance, those with missing birthdate, sex, or postal code information, and those who received the BNT162b2 (Pfizer) vaccine, a non-Health Canada-authorized vaccine, or a dose of any COVID-19 vaccine prior to July 28, 2022. Children who were tested <14 days after their first vaccine dose and those with another positive test ≤90 days before specimen collection were also excluded.

Overall, the data suggest that two doses of the Moderna vaccine provide initial protection against symptomatic SARS-CoV-2 infection and COVID-19-related hospitalization in children aged 6 months to 5 years.