Protection of vaccines against covid decreases after 6 months, study shows

The protection against covid-19 offered by two doses of vaccines from Pfizer/BioNTech and Oxford/AstraZeneca starts to decrease within six months, which shows the need for booster doses, according to a study carried out by researchers in the United Kingdom.

The British ZOE Covid study found that, in the case of the Pfizer/BioNTech vaccine, the effectiveness one month after the second dose, which is 88%, drops to 74% after five or six months. For AstraZeneca’s immunizer, the effectiveness dropped from 77% one month later to 67% after four or five months.

The study was based on data from more than 1 million users of an app, comparing infections reported by the vaccinated participants themselves with cases in an unvaccinated control group.

Data from younger people, however, are needed because participants vaccinated up to six months ago tend to be older, as this age group was prioritized when the first vaccines were approved, the study authors said.

ZOE Ltd was founded three years ago to provide personalized nutrition guidance based on exam sets. The company’s ZOE Covid Symptom Study app is a non-profit initiative in collaboration with King’s College London and funded by the Department of Health and Welfare.

In a future worst-case projection, protection could drop to less than 50% for older people and health care professionals by winter, said Tim Spector, co-founder of ZOE Ltd and lead author of the study.

“He’s calling attention to the need for some action. We can’t just wait to see protection slowly diminish while cases are still high and the chance of infection is still high,” Spector told the BBC.

The UK and other European nations are planning a booster campaign against covid-19 later this year, since experts said it may be necessary to administer the third dose to the elderly and the most vulnerable starting in September.

The US government is preparing to offer third booster shots, starting in mid-September, to Americans who received their initial shots more than eight months ago.

“This is a reminder that we cannot rely on vaccines alone to prevent the spread of covid-19,” said Simon Clarke, associate professor of cell microbiology at the University of Reading, who was not involved in the study.