The research by Sheffield and Oxford Universities looked at the immune response in 237 health workers and found that the Pfizer vaccine generated antibody and T-cell responses that would help fight off a Covid-19 infection in 99 per cent of people.
It also boosted the immune response in those who had previously been infected and already had some natural immunity.
After a second dose of the vaccine the protection was stronger across all groups.
The findings support the controversial decision by the UK government to delay the second dose of the Pfizer vaccine for up to 12 weeks, in order to vaccinate more people with first doses.
There had been concern among NHS staff working on the frontline that they were being put at greater risk by having the second dose delayed but this study appears to show that would not be the case. While the study looked at younger working age healthcare staff it did not include older age groups who can have poorer immune responses to vaccinations.
Dr Thushan de Silva, from the University of Sheffield, said: “Our study is one of the largest and most comprehensive accounts of the immune response to one dose of Pfizer/BioNTech vaccine comparing previously infected and infection-naive individuals.
“Our results demonstrate that T cell and antibody responses induced by natural infection are boosted significantly by a single dose of vaccine. While the response to a single dose was lower in infection-naïve individuals, it was still equivalent or better than the immunity in previously infected individuals before it is boosted by vaccination.”
Between December and February 2021, researchers analysed blood samples from 237 healthcare workers and found the vaccine increased the variety of cells that could fight the infection with cells able to recognises different parts of the spike protein which juts out from the main cell of the virus.
This could be crucial in protecting people against different variants of the virus, which often involve mutations in the spike protein. The more elements of the protein that can be detected by the body, the greater the protection.
The ability of antibody cells to recognise and lock on to the spike protein is what provides protection from the virus.
In people who had not had Covid before, the Pfizer vaccine led to an immune response that was as strong as people who had the virus previously after just one dose.
After just one dose of the vaccine people who had the virus before had a seven times higher level of antibodies and six times higher levels of T-cells than those who had not been infected before.
Eleanor Riley, professor of immunology at the University of Edinburgh, said: “This large, well-controlled study of UK health care workers demonstrates that a single dose of the Pfizer/BioNtech Covid-19 vaccine induces antibody and T cell responses comparable to those seen after natural infection.
“As natural infection has been shown to confer greater than 80 per cent protection against reinfection, these data offer considerable reassurance that JCVI’s somewhat controversial decision to recommend a 12 week interval between Covid-19 vaccine doses is a safe, effective and pragmatic approach to maximising public health given current constraints.”
She added: “Importantly, this study shows that vaccination of previously infected individuals not only boosts their immune responses but also broadens the repertoire of immune responses to SARS-CoV-2 and, in so doing, enhances the response to several variants of concern including the so-called Kent, South African and Brazilian variants. These data demonstrate the importance of vaccinating everyone, including people who have already been infected.”
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