A British study found that Astra and Pfizer vaccines lose effectiveness against Delta

A large British study showed that the COVID-19 vaccines produced by Pfizer and AstraZeneca are less effective against the delta variant.

The Pfizer vaccine and BioNTech messenger RNA lost efficacy in the first 90 days after a full vaccination, although those injections and the AstraZeneca syringe are still able to prevent most cases of coronavirus infection. When the vaccinated people had delta, they had levels of the virus in their bodies similar to those who did not receive the injection, supporting a recent evaluation by the Centers for Disease Control and Prevention.

The findings are likely to fuel calls for booster doses for those fully vaccinated, even as countries around the world continue to lack adequate supplies to inject the first few doses. The United States indicated on Wednesday that Americans who received two doses of the mRNA vaccine from Pfizer-BioNTech or Moderna would be able to receive a third dose after eight months. The UK authorities are still deciding how far reinforcements should be managed. In Israel, which began giving third doses of Pfizer-BioNTech this month, preliminary results show it was 86% effective for people over the age of 60.


The UK survey, conducted by Oxford University and the Office for National Statistics and released Thursday in a preliminary version, analyzed more than 3 million PCR tests from a random sample of people to get a detailed picture of infection patterns, with delta becoming the dominant variant this year.

Simon Clarke said, “We are looking at real-world data on the performance of two vaccines here, rather than data from clinical trials, and all datasets show how the delta variant attenuated the efficacy of Pfizer and AstraZeneca injections.” Associate Professor of Cellular Microbiology at the University of Reading.

About four and a half months after the second dose, Pfizer’s injection is likely to be on par with Astra in preventing infections with a higher viral load, said Quinn Boyles, the principal investigator at Oxford who helped lead the study. There was no statistically significant difference in the effectiveness of the Astra shot over time.

Sarah Walker, professor of medical statistics and epidemiology at Oxford, who helped lead the study, said these findings cast further doubt that herd immunity can be achieved through vaccination.


“The hope was that unvaccinated people would be able to protect themselves by vaccinating a lot of people,” Walker said. “The high levels of virus that we’re seeing in these infections in vaccinated people is consistent with the fact that unvaccinated people would be more at risk, I’m afraid.”

One important piece of the puzzle still missing is data showing how much vaccines go on to protect against hospitalizations and severe COVID cases over time, said Penny Ward, visiting professor of pharmaceutical medicine at King’s College London, who was not involved in the study. The findings may also support giving a booster dose of the mRNA vaccine to people who have received the Astra vaccine, which uses a different technology, Ward said in a statement. They are also showing the need for better treatments for COVID, he said.

“There is no vaccine that completely protects against delta-type infection,” Ward said. “The low hospitalization rate observed so far suggests that, in this sense, at least, vaccines protect people from severe COVID-19 infection.”

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