Research conducted in Britain by experts from the University of Oxford shows that the protection offered by the two main vaccines against COVID-19 utilized in the country in the midst of the transformation of the mutant Delta strain of the new coronavirus into the dominant is reduced within three months.
Another finding of this study is that those infected with SARS-CoV-2 after receiving two doses of either the Pfizer / BioNTech or AstraZeneca vaccine may be at greater risk if they become infected with the Delta Mutation than with other mutations.
The study, based on more than three million samples taken across the UK, showed that 90 days after the second dose, the effectiveness of the Pfizer / BioNTech vaccine was reduced to 75% and that of AstraZeneca to 61% in terms of Delta infection prevention.
Two weeks after the second dose, their effectiveness is 85% and 68%, respectively.
The reduction in effectiveness is higher among people 35 years of age and older than among younger people.
"Both of these vaccines, after the two doses, are doing very well against Delta (…). "When you start too high you have a way to go," said Sarah Walker, a professor of medical statistics at Oxford and head of research (see https://www.ndm.ox.ac.uk/).covid-19/covid-19-infection-survey / results / new-studies). Walker was not involved in the AstraZeneca vaccine study, as the drug was developed by immunologists at the University of Oxford.
The authors of the study avoided making predictions about the further reduction of the effectiveness of the two vaccines over time, however they estimated that their effectiveness will be roughly similar 4-5 months after the second dose.
Highlighting the increased risk of Delta variant infection, the researchers noted that those who were infected despite being fully vaccinated tended to have a viral load similar to that of the unvaccinated - unlike when the Alfa variant was still predominant. The findings by Oxford University scientists are generally consistent with the analysis of the Centers for Disease Control and Prevention (CDC), the US federal public health service, and are being released at a time when Washington is announcing that , booster doses of vaccines due to increased Delta mutation infections.
Joe Biden's government has cited data indicating that the protection offered by vaccines is declining over time.