People who have received two doses of the Pfizer vaccine have been found to have strong T-cell responses against the Kent and South African variants of Covid, suggesting that the vaccine will continue to protect against serious disease in the coming months.
In the first study to test immune responses against the variants circulating in populations, researchers found that although antibody responses against the new variants were blunted, they may still be high enough to protect most people from becoming infected, after a second dose of vaccine has been given.
Although previous studies had suggested that antibodies from those vaccinated with the Pfizer/BioNTech jab could recognise and neutralise viruses carrying some of the individual mutations found in the South African and Kent variants – albeit at slightly lower levels compared with previous variants – these were tested on engineered viruses rather than ones isolated from real patients.
These studies also did not look at T cells, which annihilate virus-infected cells and support the production of antibodies. Both immune responses help provide lasting protection after vaccination, but antibody responses are easier to measure.
William James, a professor of virology at the University of Oxford, and his colleagues took blood samples from people who had recovered from Covid-19, and health workers who had received either one or two doses of the Pfizer/BioNTech vaccine. They also obtained isolates of the B117 and B1.351 virus variants first identified in Kent and South Africa, and of an older variant similar to those circulating a year ago. Antibodies and T cells from the individuals were then tested against these viruses to see how well they performed.
The study, which has not yet been reviewed by other scientists, found that people’s antibodies were moderately effective against the original virus after their first dose of vaccine, less effective against the Kent variant, and were unable to neutralise the South African variant.
However, they had strong T-cell responses against all known variants after the first jab. “It may not necessarily protect you against infection, but it’s very likely that this first dose will make it much easier for your immune system to make a good response the next time around,” said James. “We think this is why that second dose produces such a good strong antibody response, because the T cells are already there, ready to react.”
The discovery that people who have recovered from Covid-19 and those who have received at least one dose of vaccine possess T cells capable of responding to the new variants is encouraging, because it suggests the T cells are recognising different regions of the spike protein to the antibodies. It could imply they will be more resilient to future variants. “It doesn’t promise you won’t get ill from the new variants, but it does suggest there’s something to work from and that your immune system can respond to them,” said James.
People’s antibody responses were also boosted by the second Pfizer jab. “In more than 90% of cases, the antibodies that people are generating after the second dose are up at the sort of level that neutralises the virus and which we would expect to protect them from infection,” said James. “We’re pretty confident that they’ll be protected from infection by the South African strain and the Kent strain, as well as the [original] strain of the virus.
“This virus hasn’t finished evolving, but I think that as long as the vaccines get rolled out, and people get those second doses, we’re going to be in a much better position by the summer than we are now,” said James.
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