The effectiveness of Pfizer-BioNTech and Oxford-AstraZeneca vaccines against SARS-CoV-2 infection is reduced by the Delta variant. This is how it is determined a new study conducted by the University of Oxford in association with the Office of National Statistics (ONS) and the Department of Health and Social Care (DHSC).
The job, published as a prepress, compares in more than 500,000 participants the protection of COVID-19 vaccines against infections before and after May 17, 2021, when Delta became the main variant in the UK. It also analyzes in detail how effectiveness changes over time, as well as other factors such as a previous infection
In this sense, two doses of either vaccine still provided at least the same level of protection as having suffered from natural virus infection. Also, people who had been vaccinated after being infected with COVID-19 had even more protection than vaccinated people who had not had COVID-19 before.
Nevertheless, vaccinated people infected with the Delta variant had the same SARS-CoV-2 viral load as unvaccinated people. In contrast, people infected with the Alpha variant had much lower peak virus levels after vaccination.
“We still don’t know what the percentage of transmission in people who contract COVID-19 after being vaccinated. For example, they can have high levels of virus for shorter periods of time, so it is essential that as many people as possible are vaccinated, both in the UK and around the world, “he said. Sarah Walker, Professor of Medical Statistics and Epidemiology at the University of Oxford and Principal Investigator and Academic Leader of the COVID-19 Infection Survey.
Comparison between vaccines
The study has also compared the efficacy between the different vaccines and the duration of their protection:
- A single dose of Modern vaccine presents a similar or greater efficacy against Delta variant than the single doses of the other vaccines.
- Two doses by Pfizer-BioNTech they have one greater initial effectiveness against new COVID-19 infections, but decreases faster compared to two doses of the Oxford-AstraZeneca vaccine.
- After four / five months, the effectiveness of the Pfizer-BioNTech and Oxford-AstraZeneca vaccines would be similar. However, the researchers insist on studying the long-term effects.
- The time between doses does not affect to efficacy in preventing new infections, but younger people have even more protection than older people.
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It is the first study to show how protection against COVID-19 infections changes over time after the second vaccination in a large group of adults from the general population.
Koen PouwelsSenior Researcher at the University of Oxford’s Nuffield Population Health Department, noted that while vaccines reduce the chance of contracting COVID-19, “they don’t eliminate it. More importantly, our data shows the potential for people vaccinated to transmit COVID-19 to others, and the importance of testing and self-isolation to reduce the risk of transmission ”.
