A new study focused on the two most administered Covid-19 vaccines: Pfizer-BioNTech and AstraZeneca. Scientists analyzed how these two vaccines protect the immune system against several SARS-CoV-2 strains, including the dominant one in the U.S.
The British Study used more than three million swab samples
To determine the efficacy of the two above mentioned vaccines, Oxford researchers used more than three million nose and throat swabs obtained from all over the U.K. The British Office of National Statistics and the Department of Health and Social Care collaborated with the study. The swab samples were from before the Delta strain became dominant, around 2.59 million, and afterwards, around 810.000.
The impact of the Delta strain on two of the most administered vaccines worldwide helps researchers understand how and when they need to administer the third dose and how fully vaccinated people get infected.
Findings and conclusions
After careful analysis of all sample sand statistics, the study indicated that 90 days after the second dose of Pfizer is administered, the efficacy against the Covis-19 infection is 75%. The efficacy in preventing the infection for AstraZeneca is 61% after 90 days since reaching complete vaccination.
There were different levels of efficacy depending on age as well. It seems that less efficacy has been registered at people 35 or older. After being fully vaccinated, a person is protected for 4 to 5 months.
The Delta strain is more dangerous than the Alpha
At the beginning of the pandemic, the Alpha strain of the Covid virus was prevalent in the U.K. Since then, other mutations have entered the country, and the one that originated in India, the Delta strain, is much more dangerous than others.
The study determined that fully vaccinated people infected with the Delta strain have a viral load very similar to that of unvaccinated individuals. This means that fully vaccinated people can spread the infection. This was not the same when researchers analyzed the Alpha variant. The conclusion is that available vaccines prevent the disease and death or hospitalization, but they prevent infection less.