Pfizer and AstraZeneca’s COVID-19 vaccines are less effective against the Delta variant of coronavirus than the Alpha variant, according to a study led by researchers at the University of Oxford.
The researchers did note, however, that the Delta, Pfizer-BioNTech vaccine, and Oxford-AstraZeneca preventive, known as Covishield in India, continue to provide adequate protection against new infections.
According to the researchers, two doses of either vaccine provided at least the same level of protection as having had COVID-19 before through natural infection.
Between December 1, 2020 and May 16, 2021, the researchers examined 2580,021 test results from nose and throat swabs taken from 384,543 participants aged 18 and up.
In addition, between May 17, 2021 and August 1, 2021, they examined 811,624 test results from 358,983 participants.
The study, which has yet to be peer-reviewed, discovered that people who were vaccinated after being infected with COVID-19 had even more protection than vaccinated people who had never been infected with COVID-19.
Delta infections after two vaccine doses, on the other hand, had similar peak levels of virus as unvaccinated people, according to the researchers.
Peak virus levels in those infected after vaccination were much lower with the Alpha variant, they reported.
“We don’t yet know how much transmission can occur from people who get COVID-19 after being vaccinated — for example, they may have high levels of virus for shorter periods of time,” said Sarah Walker, an Oxford professor.
However, the fact that they can have high levels of virus suggests that people who have not yet been vaccinated may not be as protected against the Delta variant as we hoped. This means that “it is critical that as many people as possible get vaccinated,” Walker explained.
Researchers from the UK’s Office of National Statistics (ONS) and the Department for Health and Social Care (DHSC) discovered that a single dose of the Moderna vaccine is as effective as a single dose of the other vaccines against the Delta variant.
According to the researchers, two doses of Pfizer-BioNTech vaccine have greater initial efficacy against new COVID-19 infections, but this declines faster than two doses of Oxford-AstraZeneca vaccine.
The results indicate that the effectiveness of these two vaccines would be comparable after four to five months; however, the researchers stated that long-term effects would need to be studied.
According to the study, the time between doses has no effect on the effectiveness of vaccination in preventing new infections, but younger people benefit from vaccination even more than older people.
“The fact that we saw no effect of the interval between the first and second doses, and the greater effectiveness of having two doses rather than one, supports the decision to reduce this to eight weeks now that Delta is the main variant of concern in the UK,” said Koen Pouwels, senior researcher at Oxford University.
Vaccinations reduce the risk of contracting COVID-19 but do not eliminate it. More importantly, our findings show that vaccinated people can still transmit COVID-19 to others, emphasising the importance of testing and self-isolation to reduce transmission risk,” Pouwels said.
The study compared COVID-19 vaccine protection against infections before and after May 17, 2021, when Delta became the main variant in the UK.
It also examined how effectiveness changes over time, as well as other factors such as previous infection.
The Delta variant has blunted the effectiveness of both the Pfizer and AstraZeneca vaccines, according to Simon Clarke, Associate Professor at the University of Reading in the United Kingdom.
“Of particular concern is that Delta significantly reduces the AstraZeneca vaccine’s effectiveness, and it appears to offer no more protection than someone would get from having COVID-19 and building some natural immunity,” Clarke, who was not involved in the study, said.
“The Pfizer jab provided more initial protection than the AstraZeneca jab, but after about five months, the level of immunity dropped to about the same level seen for both vaccines studied,” he added. PTI