The protection that people who took the two doses of the Pfizer and AstraZeneca vaccines receive against Covid-19 decreases six months after the application of the immunizer, according to researchers in the United Kingdom.
The finding reinforces the need to apply booster doses in the population, the study authors indicate.
According to the survey, the effectiveness of Pfizer’s vaccine to prevent infection by the coronavirus reaches 88% in the month following the application of the second dose, but drops to 74% after a period that varies between five and six months.
In the case of AstraZeneca’s immunizer, the effectiveness drops from 77% to 67% after a period of between four and five months.
The finding was made from an analysis of data used in the Zoe Covid study, which collected health information from more than 1 million people through an app.
To reach this result, the researchers compared the number of infections reported by app users who had taken all doses of the two immunizations in question with a control group made up of unvaccinated people.
Tim Spector, founder of Zoe and scientist responsible for the study, said that, in the worst-case scenario, the protection provided by these two immunizers for seniors and health professionals could drop below 50% after a period.
“This brings into focus the need to act. We cannot sit and wait while protection slowly deteriorates, while the number of infections remains high and the chance of infection remains high,” he told the BBC TV network.
The authors pointed out, however, that further analysis of the effectiveness of vaccines in younger people is still needed. That’s because the survey basically only used data from older people — most of those who took the two doses more than six months ago are elderly.
Zoe, the company responsible for the data used in the study, was founded three years ago with the aim of offering personalized food and nutrition consulting.
The app she created during the pandemic, the Zoe Covid Symptom Study, is a non-profit initiative made in collaboration with King’s College London and funded by the UK Department of Health and Social Services.
The UK and other European countries are planning a booster campaign against the Covid-19 vaccine later this year, after doctors and researchers began to indicate the need to give a third dose to the elderly and the most vulnerable groups.
The US government is already preparing to provide the third dose starting in September — the target is people who took the first two more than eight months ago.
“It’s a reminder that we can’t rely on vaccines alone to curb Covid’s spread,” said Simon Clarke, associate professor of cell microbiology at the University of Reading, who was not involved in the study.
He urged caution about the results, as they may have been influenced by the spike in the overall UK caseload in July.
Another study that also looked at British public health found last week that the protection afforded by Pfizer and AstraZeneca vaccines against the current prevalent variant of the coronavirus, delta, wears off within three months.
An Oxford University study found that 90 days after applying the second dose of Pfizer or AstraZeneca, the effectiveness in preventing infections dropped to 75% and 61%, respectively — from an original protection of 85% and 68%, reported two weeks after the first dose.
Translation by Paulo Migliacci