And the study found Oxford universityAnd based on more than 3 million swabs from the nose or throat across Britain, it was 90 days after the second dose of the vaccine. Pfizer or AstraZenecaThe efficiency of the first in preventing infection decreased by 75 percent, and the second by 61 percent.
This represented a decrease of 85 percent for Pfizer and 68 percent for AstraZeneca observed two weeks after the second dose. The decline in effectiveness was more pronounced in those over the age of 35 years.
“Both vaccines, after two doses, still worked really well against delta,” said Sarah Walker, professor of medical statistics at Oxford who led the study.
The researchers did not specify the extent to which protection decreased over time, but they indicated that the efficiency of the two vaccines that were studied will converge after 4 to 5 months after the second dose.
Highlighting the increased risk of infection from the delta strain, the study also showed that those who become infected despite being fully vaccinated tend to have a viral load similar to those without the vaccine, a clear regression from when the alpha strain was still prevalent in Britain.
The results of the Oxford study agree with an analysis by US Centers for Disease Control and Prevention Including, as it comes as the US government develops plans to make a third booster dose of vaccines widely available next month, with the increase in infections with the Delta strain. She attributed this to data indicating a decline in protection from the vaccine over time.
Israel began vaccinating with third doses of the Pfizer vaccine last month to counter a rise in local infections caused by the Delta strain.
Several European countries are also expected to start providing booster doses for the elderly and those with weakened immune systems.
Pfizer said the effectiveness of its vaccine declines over time.
AstraZeneca said last month that it was still studying how long its vaccine would protect and whether a booster dose would be needed to maintain immunization against the virus.
“The fact that we’re seeing … a larger viral load suggests (…) that herd immunity may actually become more difficult,” said study co-author Quinn Boyles, also from Oxford University.
Herd immunity occurs when a large enough section of the population is immune to a pathogen, either through vaccination or previous infection, which stops the growth of infected numbers.