Two of the main vaccines against Covid-19 lose their effect against the virus as time goes on, according to a new study by scientists at Oxford University.
Caveat: The study has yet to be published in an official medical journal, and should therefore be considered unconfirmed foe the time being.
The study looked at 2.6 million nose- and throat-swabs taken from more than 384,500 volunteers in the period from December 2020 and mid-May this year, as well as 811,600 test results from 358,983 adults between mid-May and 1 August 2020.
The results showed that the AstraZeneca vaccine – which was developed in conjunction with Oxford University – had fallen in effectiveness from 80% protection after two weeks to 61% after 90 days.
The Pfizer vaccine, developed with BioNTech and manufactured in Puurs in Antwerp province, dropped from 95% protection after seven days to 75%, 90 days after a second vaccination.
An important factor in the difference is thought to be the arrival of new variants of the SARS-CoV-2 virus – first the alpha or British variant in the earlier period of the test, and later the delta or Indian variant in the later stage.
Vaccines are constantly being adjusted and refined to cope with the arrival of new variants of a virus – as happens annually when you have to have your flu shot renewed.
But a vaccine that has already been administered cannot be adjusted to take account of a new variant that comes along at such a rapid pace as has been occurring with the Covid variants.
"We quickly see a reduction in effectiveness, but it is not so dramatic that we need to be very concerned about this," Dutch epidemiologist Koen Pouwels, who participated in the study in Oxford, told the VRT.
"After three months, the protection is still a lot better than what the World Health Organization (WHO) initially proposed."
"Both of these vaccines, at two doses, are still doing really well against Delta,” said Sarah Walker, an Oxford professor of medical statistics and chief investigator for the survey. “When you start very, very high, you have a long way to go."
