A British study led by King’s College London found how long it takes for the protection against covid-19 provided by two doses of Pfizer and AstraZeneca vaccines to begin to wane.
According to the researchers, who analyzed the positive results of the PCR test between May and July 2021 of more than one million people who received two doses of these vaccines, protection weakens from the sixth month of immunization.
The analysis showed that protection after two doses of Pfizer decreased from 88% in one month to 74% in five to six months. In the case of AstraZeneca, the drop went from 77% to 67% in four to five months.
For Professor Tim Spector, from King’s College London (KCL), who led the study, this drop is already expected and only attests to the need for booster doses. She goes on to say that the findings may explain the recent infections that some fully vaccinated people have reported.
“Vaccines still provide high levels of protection for the majority of the population, especially against the Delta variant, so we still need as many people as possible to be fully immunized,” says Spector.
The researcher also points out that some people may have already received a natural booster because they already had a covid infection. “So, effectively, they will have taken three vaccines”, he says.