New study finds Pfizer, AstraZeneca vaccines have lower effe
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A new study led by researchers at the University of Oxford has revealed that the protection from Pfizer and AstraZeneca Covid-19 vaccines against the now prevalent Delta variant wanes within three months. The efficacy of the Pfizer or the AstraZeneca vaccine in preventing infections slipped to 75 per cent and 61 percent respectively, 90 days after a second shot of the vaccines down from 85 per cent and 68 per cent, respectively, seen two weeks after the second dose.

More than 3,00,000 test results from nose and throat swabs were analysed. Samples were taken from 384,543 participants -- aged 18 years or older between December 1, 2020 and May 16, 2021. Researchers also analysed 811,624 test results from 358,983 participants between May 17, 2021, and August 1, 2021. The study compared protection from infections from Covid-19 vaccines before and after May 17, 2021, when Delta became the main variant in the UK.



The UK study suggested that participants, who were vaccinated after already being infected with Covid-19, had more protection than vaccinated individuals who had not had Covid-19 infection before. However, Delta infections after two vaccine doses had similar peak levels of viral load as those in unvaccinated people, the researchers said. Also, with the Alpha variant, peak virus levels among those infected post-vaccination turned out to be much lower.


"Two doses of Pfizer-BioNTech have greater initial effectiveness against new Covid-19 infections, but this declines faster compared with two doses of Oxford-AstraZeneca. Results suggest that after four to five months effectiveness of these two vaccines would be similar however, long-term effects need to be studied," the study further said. The researchers also found that a single dose of the Moderna vaccine has similar or greater effectiveness against the Delta variant as single doses of the other vaccines.


The time between doses does not affect effectiveness in preventing new infections, the study said. However, younger people have even more protection from vaccination than older people, it said.

"The fact that we did not see any effect of the interval between first and second doses, and the greater effectiveness of having had two doses, rather than one dose, supports the decision to reduce this to eight weeks now Delta is the main variant of concern in the UK," said Koen Pouwels, senior researcher in Oxford University.

Simon Clarke, Associate Professor at the University of Reading in the UK, said the real-world data of how two vaccines are performing show the Delta variant has blunted the effectiveness of both the Pfizer and AstraZeneca jabs. "Of particular concern, the AstraZeneca vaccine's effectiveness is reduced substantially by Delta and it appears to offer no more protection than what someone would get from having Covid-19 and building some natural immunity," Clarke, who was not involved in the study, said.