The study compared effectiveness of the two vaccines over the period of January to July 2021, in which the Alpha and Delta were prevalent.
Both vaccines’ effectiveness was reduced by the Delta variant but Pfizer/BioNTech had a more pronounced reduction. Moderna was 76% effective against infection with Delta in comparison to Pfizer/BioNTech’s 42% effectiveness.
Furthermore, it found that Moderna conferred a two-fold risk reduction against breakthrough infection compared to Pfizer/BioNTech. Notably there was no difference in ICU admissions and no deaths recorded in the vaccinated population.