The Covid-19 vaccine from Pfizer and BioNTech appears to protect against viruses carrying at least one of the key mutations found in two coronavirus variants that are causing rapid spread across the UK, according to a study.
However, further research is needed to confirm that the level of protection afforded by the vaccine is as high as against older variants – and to ensure it protects against viruses carrying another significant mutation found in the South African variant.
The emergence of new, and apparently more transmissible coronavirus variants has prompted widespread concern about whether existing vaccines, including the Pfizer/BioNTech jab, will remain effective.
The Pfizer/BioNTech Covid jab is an mRNA vaccine. Essentially, mRNA is a molecule used by living cells to turn the gene sequences in DNA into the proteins that are the building blocks of all their fundamental structures. A segment of DNA gets copied (“transcribed”) into a piece of mRNA, which in turn gets “read” by the cell’s tools for synthesising proteins.
In the case of an mRNA vaccine, the virus’s mRNA is injected into the muscle, and our own cells then read it and synthesise the viral protein. The immune system reacts to these proteins – which can’t by themselves cause disease – just as if they’d been carried in on the whole virus. This generates a protective response that, studies suggest, lasts for some time.
The two first Covid-19 vaccines to announce phase 3 three trial results were mRNA-based. They were first off the blocks because, as soon as the genetic code of Sars-CoV-2 was known – it was published by the Chinese in January 2020 – companies that had been working on this technology were able to start producing the virus’s mRNA. Making conventional vaccines takes much longer.
Adam Finn, professor of paediatrics at the Bristol Children’s Vaccine Centre, University of Bristol
In the study, yet to be peer-reviewed, Pfizer together with researchers from the University of Texas medical branch took blood samples from 20 people who had already been immunised with the Pfizer/BioNTech vaccine. They tested the ability of their antibodies to neutralise coronaviruses engineered to harbour a N501Y mutation – an alteration in the spike protein of the virus, which is a target for vaccines and may also increase its ability to infect human cells.
Doing so revealed that vaccinated individuals had developed antibodies capable of working against viruses harbouring the N501Y mutation. However, one of the important mutations in the South Africa variant, named E484K, has not yet been studied.
Pfizer said it had tested 16 different mutations in the strains and none of them have had any significant impact on how the vaccine works. Further studies are planned on the other mutations.
“This is good news, mainly because it is not bad news,” saidStephen Evans, a professor of pharmacoepidemiology at the London School of Hygiene & Tropical Medicine. “Had the opposite result been found, that the vaccine did not seem to have efficacy against the variation of the virus studied, that would have been bad and very concerning. But it does not yet give us total confidence that the Pfizer (or other) vaccines will definitely give protection. We need to test this in clinical experience and the data on this should be available in the UK within the next few weeks.”
One limitation is that the researchers did not construct Sars-CoV-2 containing the full set of spike mutations found in either the UK or South African variant. It is possible the different mutations might interact with one another to affect the overall structure of the spike protein, which might influence the vaccine’s effectiveness. So, ideally, the mutations should be tested together.
On the other hand, vaccines work by stimulating the immune response, which generates a highly diverse library of antibodies against different parts of the virus. “Therefore we would expect a person’s immune response to be diverse enough to cope with some changes to the virus structure,” said Deborah Dunn-Walters, the chair of the British Society for Immunology Covid-19 and Immunology taskforce, and professor of immunology at the University of Surrey.
“It is reassuring that Pfizer are closely monitoring whether variants of the Sars-CoV-2 virus can escape the immune responses elicited by their Covid-19 vaccine, and that so far there is no evidence that the mutations tested have made any difference to antibody ability,” she added.
“Of course, this needs constant monitoring, and the South African variant has a mutation of concern, but even if we did see any differences, the technology used to make the vaccines means they can be changed quite quickly if necessary.”