Epidemiology: Moderna vaccine effective against Alpha and Beta variants

The Moderna vaccine was 100% effective against the Alpha variant of SARS-CoV-2 and 96% effective against the Beta variant at 14 days after administration of the second dose, according to a study of vaccinated people living in Qatar, published in Nature Medicine.

The first immunization with the Moderna vaccine in Qatar was recorded on 28 December 2020, but mass vaccination did not begin until late February 2021. As the vaccination campaign expanded, Qatar experienced two back-to-back waves of SARS-CoV-2 infections that were triggered by the introduction and expansion of the Alpha (B.1.17) and Beta (B.1.351) variants of concern. This presented a unique opportunity for assessing the real-world effectiveness of the Moderna vaccine against infection with these variants.

Hiam Chemaitelly, Laith Abu-Raddad and colleagues analyzed data from 256,037 people in Qatar who had received at least one dose of the vaccine and 181,304 who had completed the two-dose regimen between 28 December 2020 and 10 May 2021. Qatar has a young, diverse population in which only 9% of residents are older than 50 years and 89% are expatriates from more than 150 countries. The median age of the cohort for estimating vaccine effectiveness against the Alpha variant was 31 years; this was 32 years for the Beta variant. The authors found that the vaccine was 88% effective against the Alpha variant at 14 days after the first dose and 100% effective after the second dose (after 14 days). For the Beta variant, the vaccine was 61% effective at 14 days after the first dose and 96% effective after the second dose (after 14 days). The authors also found that the vaccine was highly effective against severe, critical or fatal COVID-19 disease due to any SARS-CoV-2 infection (predominantly from Alpha and Beta variants): 82% effective and 96% effective after the first dose and second dose, respectively.

The authors note that given Qatar’s young population, the estimated effectiveness of the Moderna vaccine in other older populations remains to be determined.