The protection against the coronavirus conferred by the Pfizer and AstraZeneca vaccines decreases significantly after 6 months, indicated a British study on Wednesday (25), whose authors defend booster doses.
One month after the second dose, the efficacy of the Pfizer vaccine is 88%, a protection against possible infections that drops to 74% between five and six months after the injection, according to the latest analysis of the Zoe Covid study.
For the AstraZeneca vaccine, effectiveness ranges from 77% one month after the second dose to 67% between four and five months later.
The study was conducted with data from around 1 million users of the Zoe app, launched by a private group of the same name.
King’s College London researchers and Zoe’s team analyzed data on infections that occurred between May 26 and July 31, 2021 in vaccinated people who downloaded the app between December 8 and July 3, 2021.
The British vaccination campaign, which applied a second dose to 77% of those aged over 16, gave priority to the elderly and people at risk, as well as health professionals.
In the opinion of the King’s College researchers, protection therefore declined further in these groups.
Professor Tim Spector, the scientist who led the project, warned that this could be “less than 50% in seniors and winter health workers.”
If this number refers to infections rather than serious forms, it could mean “an increase in hospitalizations and deaths” if the country faces high levels of infection and a highly contagious variant.
The researcher considers, then, “urgent to provide booster doses”, as well as to study whether it is convenient to immunize minors based on the available vaccines.
Several countries are studying administering a booster dose, including the United Kingdom, which wants to propose the vaccine to people at risk from September, despite the reluctance of the WHO (World Health Organization).