A woman looks on as she receives the COVID-19 booster vaccine, amid the coronavirus disease (COVID-19) pandemic, at Midland House in Derby, Britain, September 20, 2021. (Photo: REUTERS)

The "COV-Boost" study was cited by British officials when they announced that Pfizer and Moderna were preferred for use in the country's booster campaign, but the data has only been made publicly available now. 

The study found that six out of the seven boosters examined enhanced immunity after initial vaccination with Pfizer-BioNTech's vaccine, while all seven increased immunity when given after two doses of AstraZeneca's vaccine.