A real-world study by the UK Health Security Agency shows that boosters significantly increase protection against illness from Covid-19. The study found that two weeks after a booster dose, protection levels increased to 93.1% for those who had AstraZeneca for their first two doses and 94% for those who had Pfizer.
In October 2021 Pfizer announced results from phase 3 clinical trials of their vaccine as a booster, showing that it was extremely effective against preventing illness from Covid-19.
In the 5,000 people who received the booster dose, 5 of them developed Covid-19 illness. In the 5,000 people who didn’t get the booster (but were double vaccinated) there were 109 cases of Covid-19
https://www.bhf.org.uk/informationsu...ooster-vaccine