Strong T-cell response is good news for battle against Covid variants

Covid-19 variants may be less dangerous to vaccinated people and recovered patients than previously thought, according to researchers who found that the human body produces a strong cellular immune response to some of the most worrying new strains.

The US study, conducted by researchers at the La Jolla Institute for Immunology and the University of California, identified that T-cell responses in patients who had been vaccinated or previously infected were just as robust when faced with new variants of Covid-19 — including those first identified in Kent, Brazil, South Africa and California.

T-cells, which can “remember” past infections and kill pathogens if they reappear, are thought to have a big influence on how long people remain resistant to infection and disease. They come in several different types, including killer T-cells, helper T-cells and memory T-cells. B-cells, another essential type of white blood cell, produce antibodies.

The findings are likely to alleviate some of the concerns about new strains outsmarting the existing crop of vaccines.

“The data provide some positive news in light of justified concern over the impact of Sars-Cov-2 variants of concern on efforts to control and eliminate the present pandemic,” the paper concluded. “While it is not anticipated that circulating memory T cells would be effective in preventing Sars-Cov-2 infection, it is plausible that they can reduce Covid-19 severity,” it said.

The study, which has not yet been peer-reviewed, found that new variants had a “marginal impact” on both helper and killer T-cell responses when they were compared against the original Wuhan strain. The strains were tested against one another in the blood serum of people who had previously been infected, and people who had received the Moderna and BioNTech/Pfizer vaccine.

The research comes after worrying data emerged from Brazil where the P. 1 variant, which has since spread to more than 25 countries, was found this week to provoke a less effective antibody response among vaccinated and recovered people than earlier versions of the virus.

In the Brazilian study, released on Tuesday, researchers tested blood plasma of 20 people who had previously been infected with Covid-19 and eight people who had received the CoronaVac vaccine, developed by China’s Sinovac, against the P. 1 variant.

The team from the University of São Paulo and Campinas university found the P. 1 variant generated a six-fold decrease in antibodies compared with the variant that was circulating before it emerged late last year. The influenza vaccine was normally tweaked once it was found that a new variant in circulation reduced the level of antibodies produced by four times or more, the researchers said.

The study, which has also not yet been peer-reviewed, found that antibodies struggled to bind to P. 1’s all-important spike protein, which it uses to enter human cells. The variant has more than 17 mutations, which alter its genetic sequence from the virus originally identified in Wuhan, including three concerning changes to the spike protein.

Jeffrey Barrett, director of the Sars-Cov-2 genomics initiative at the Wellcome Sanger Institute, said the study showed there was “some cause for concern about vaccines protecting less well against P. 1”. But he also stressed that the function of T-cells should not be overlooked. 

The emergence of the P. 1 variant in the Brazilian city of Manaus was linked to a surge of cases earlier this year that overwhelmed the municipality’s health service. It quickly became the dominant strain of Covid-19 in the city and is now present in at least 17 out of 26 states in Brazil. 

Like variants of coronavirus originating in the UK and South Africa, it has been found to be more transmissible than the strains circulating in early 2020. 

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