The protection against coronaviruses provided by vaccines drops significantly after six months, according to a British study, whose authors advocate booster doses.
One month after the second dose, Pfizer’s vaccine efficacy is 88%, but protection against possible contagion 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 goes from 77% one month after the second dose to 67% between four and six months after application.
The study was based on data from nearly a million users of the Zoe application, created by a private group of the same name.
Scientists from King’s College London 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, 2020 and July 3, 2021.
The British vaccination campaign, which has already applied the second dose to 77% of people over 16 years of age, prioritized the elderly and people with comorbidities, as well as health professionals.
For scientists at King’s College, protection declined further in these groups.
Professor Tim Spector, scientist who led the project, warned that protection could be “less than 50% for the elderly and health professionals for the winter” (northern hemisphere, summer in Brazil).
If this number refers to the contagions and not the severe forms, this could imply “an increase in hospitalizations and deaths”, if the country faces high levels of infection and a highly contagious variant.
The researcher considers “urgent to predict booster doses”, as well as to study whether it is convenient to immunize minors with the available vaccines.
Several countries are studying administering a booster dose, including the United Kingdom, which wants to offer it to people with comorbidities from September, despite the reticence of the World Health Organization (WHO).