Initial research reveals that although two doses of the Pfizer BioNTech vaccine appears to have greater effectiveness against new COVID-19 infections associated with the Delta variant, its efficacy also declines faster when compared to the Oxford AstraZeneca jab.
Experts from the University of Oxford said that after four to five months, the level of protection offered by both vaccines is similar, with the AstraZeneca jab maintaining its effectiveness throughout the duration.
The results, which have not yet been evaluated, also suggest that those infected with the Delta variant after their second jab had similar peak levels of virus as the unvaccinated.
Based on their findings, the researchers said that although vaccines did not remove the possibility of getting COVID-19, they did lessen the risk and remained the most effective way to ensure protection against the Delta variant–which has become dominant in the UK.
Sarah Walker, professor of medical statistics and epidemiology at the University of Oxford, said:
We don’t yet know how much transmission can happen from people who get COVID-19 after being vaccinated–for example, they may have high levels of virus for shorter periods of time.
However, the fact that they can have high levels of virus suggests that people who aren’t yet vaccinated may not be as protected from the Delta variant as we hoped.
This means it is essential for as many people as possible to get vaccinated– both in the UK and worldwide.
The study, conducted in partnership with the Office of National Statistics (ONS) and the Department for Health and Social Care (DHSC), observed data from December 2020 to August 2021 from the COVID-19 Infection Survey.
Swab tests from more than 700,000 participants were studied from before and after May 17, 2021, when Delta became the main variant in the UK.
Studies showed that for infections with a high viral load, protection a month after the second Pfizer dose was 90% greater than an unvaccinated individual, reducing to 85% after two months and 78% after three.