News – Prior SARS-CoV-2 infection rescues B and T cell responses to variants after first vaccine dose

Tuesday, 04 May 2021

A single dose of vaccine boosts protection against SARS-CoV-2 coronavirus variants, but only in those with previous Covid-19, a study has found.

In those who have not previously been infected, after one dose of vaccine the immune response to variants of concern is substantially reduced.

The findings, published today in the journal Science and led by researchers at Imperial College London and Queen Mary University of London, along with experts at the University of Nottingham, looked at immune responses in UK healthcare workers following their first dose of the Pfizer/BioNTech vaccine.*

Professor Ana Valdes

They found that people who had previously had mild or asymptomatic infection had significantly enhanced protection against the Kent and South Africa variants, after a single dose of the mRNA vaccine. In those without prior COVID-19, the immune response was less strong after a first dose, potentially leaving them at risk from variants.

Professor Ana Valdes from the School of Medicine at the University Nottingham, PI of the Covid-19 rapid response UKRI MRC grant that funded some of the work said: “This work showcases the value of new interdisciplinary collaborations set-up at the height of the pandemic now helping us understand differences in immune responses to the vaccine”

Professor Rosemary Boyton, Professor of Immunology and Respiratory Medicine at Imperial College London, who led the research said: “Our findings show that people who have had their first dose of vaccine, and who have not previously been infected with SARS-CoV-2, are not fully protected against the circulating variants of concern. This study highlights the importance of getting second doses of the vaccine rolled out to protect the population.”

Blood samples were analysed for the presence and levels of immunity against the original strain of SARS-CoV-2, as well as the Kent (B.1.1.7) and South Africa (B.1.351) variants of concern. Along with antibodies – the Y-shaped proteins which stick to the virus and help block or neutralize the threat – the researchers also focused on two types of white blood cell: B-cells, which ‘remember’ the virus; and T cells, which help B cell memory and recognise and destroy cells infected with coronavirus.

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They found that after a first dose of vaccine, prior infection was associated with a boosted T cell, B cell and neutralizing antibody response, which could provide effective protection against SARS-CoV-2, as well as the Kent and South Africa variants.

However, in people without previous SARS-CoV-2 infection, a single vaccine dose resulted in lower levels of neutralising antibodies against SARS-CoV-2 and the variants, potentially leaving them vulnerable to infection and highlighting the importance of the second vaccine dose.

The team looked at two variants of concern, however, they think it possible that the findings will apply to other variants in circulation, such as the Brazil (P.1) and India (B.1.617 and B.1.618) variants.

It remains unclear precisely how much protection is offered by T cells. Interestingly, the mutations in the Kent and South Africa variants here resulted in T cell immunity which could be reduced, enhanced or unchanged compared to the original strain, depending on genetic differences between people.

Professor Boyton commented: “Our data show that natural infection alone may not provide sufficient immunity against the variants. Boosting with a single vaccine dose in people with prior infection probably does. As new variants continue to emerge, it is important to fast track global rollout of vaccines to reduce transmission of the virus and remove the opportunities for new variants to arise.”

Story credits

More information is available from Professor Ana Valdes from the School of Medicine at the University of Nottingham at  Ana.valdes@nottingham.ac.uk

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