A recent Canadian pre-print study found that AstraZeneca’s Vaxzevria vaccine was 82% effective in preventing hospitalization or death from the Beta and Gamma SARS-CoV-2 virus variants. Using the same benchmark, its efficacy against the Alpha and Delta variants was 87% and 90%, respectively, 21 days after administering the first dose.

The BNT162b2 vaccine from Pfizer and BioNTech had a similar efficacy after 21 days. In terms of protecting against the Beta and Gamma variants, a single dose of the BNT162b2 vaccine was 83% effective at protecting against hospitalization and death after 21 days. One dose of Moderna’s mRNA-1273 vaccine was 94% effective at the same interval.

A second dose of the Pfizer-BioNTech vaccine boosted its efficacy considerably. It was 98% effective at preventing hospitalization or death from the Beta and Gamma variants 14 days after the second dose. Its protection against other variants was similar following the second dose.

There was, however, insufficient data to assess the post-second-dose efficacy of the AstraZeneca or Moderna vaccines.

Other studies have demonstrated that an additional dose translates to a boost in effectiveness.

The Canadian study included data from 69,533 individuals with confirmed COVID-19 infections from December 2020 to May 2021 in Ontario, Canada.