Oxford study finds vaccines still work but are less effective against Delta variant of virus
Scientists have urged caution after a University of Oxford study found Covid-19 vaccines to be less effective against the Delta variant of the virus.
Although Pfizer-BioNTech and Oxford-AstraZeneca vaccines still offer good protection against Delta infections, effectiveness is reduced compared with the Alpha variant of the virus, according to the preprint study.
The study found that people infected with the Delta variant after two vaccine doses had similar peak levels of virus to those in unvaccinated people, while those with the Alpha variant had much lower levels.
Transmission risk
“Whilst vaccinations reduce the chance of getting Covid-19, they do not eliminate it,” said Koen Pouwels, senior researcher in Oxford University’s Nuffield Department of Population Health.
“More importantly, our data shows the potential for vaccinated individuals to still pass Covid-19 onto others, and the importance of testing and self-isolation to reduce transmission risk.”
The study did find that two doses of either vaccine still provided at least the same level of protection as having had Covid-19 before through natural infection.
Alexander Edwards, an associate professor in biomedical technology at the University of Reading, said the study was “excellent as it shows that although Delta is better at infecting vaccinated people than previous variants, the vaccines still work remarkably well”.
However, he added that it is still “vital to remember that even if double jabbed, you can still get infected and pass the virus on”.
Penny Ward, a visiting professor in pharmaceutical medicine at King’s College London, also urged caution, saying there was a need for “continued focus on test, trace and isolate activities to reduce the spread across the community”.
The study was conducted in partnership with the Office of National Statistics and the Department of Health and Social Care. It 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 two vaccines.
Moderna jab approved for under 18s
Meanwhile, the UK’s medicines regulator, the Medicines and Healthcare products Regulatory Agency, has approved the use of the Moderna vaccine in 12 to 17-year-olds.
“We have in place a comprehensive safety surveillance strategy for monitoring the safety of all UK-approved Covid-19 vaccines and this surveillance will include the 12- to 17-year age group,” said June Raine, MHRA’s chief executive.
“It is for the Joint Committee on Vaccination and Immunisation to advise on whether this age group should be vaccinated with the Covid-19 vaccine made by Moderna as part of the deployment programme.”