A single dose of the vaccine boosts protection against variants of the SARS-CoV-2 coronavirus, but only in those who have previously had COVID-19, a study found.
In those who have not been infected before and have so far received only a single dose of the vaccine, the immune response to the variants of concern may be insufficient.
The results, published today in the journal Science and led by researchers from Imperial College London, Queen Mary University London and University College London, examined the immune responses of UK health workers at Barts and Royal Free hospitals after their first dose Pfizer / BioNTech vaccine.
They found that people who had previously had a mild or asymptomatic infection had significantly improved protection against the Kent and South African variants after a single dose of the mRNA vaccine. In those without previous COVID-19, the immune response was weaker after a first dose, leaving them potentially at risk for variants.
Professor Rosemary Boyton, Professor of Immunology and Respiratory Medicine at Imperial College London, who led the research, said: “Our results show that people who received their first dose of the vaccine and who did not not previously infected with SARS-CoV-2, are not fully protected against circulating variants of concern. This study underlines the importance of the implementation of second doses of the vaccine to protect the population. “
Blood samples were analyzed for the presence and levels of immunity against the original strain of SARS-CoV-2, as well as variants from Kent (B.1.1.7) and South Africa (B. 1.351) of concern. Besides antibodies – the Y-shaped proteins that stick to the virus and help block or neutralize the threat – researchers also focused on two types of white blood cells: B cells, which “remember” the virus; and T cells, which help B cell memory and recognize and destroy cells infected with the coronavirus.
They found that after a first dose of vaccine, a previous infection was associated with an enhanced response of T cells, B cells, and neutralizing antibodies, which could provide effective protection against SARS-CoV-2, as well as against variants from Kent and South Africa.
However, in people without previous infection with SARS-CoV-2, a single dose of the vaccine resulted in lower levels of neutralizing antibodies against SARS-CoV-2 and its variants, making them potentially vulnerable to infection. and stressing the importance of the second dose of vaccine.
The team looked at two variants of concern, but believe the results may apply to other variants in circulation, such as the Brazilian (P.1) and Indian (B.1.617 and B. 1.618).
It is not clear exactly what protection is offered by T cells. Interestingly, the mutations in the Kent and South African variants here have resulted in T cell immunity that may be reduced, improved, or unchanged from that. to the original strain, based on genetic differences between people.
Professor Boyton commented: “Our data shows that natural infection on its own may not provide sufficient immunity against the variants. Stimulation with a single dose of vaccine in people already infected probably does. As variants continue to emerge, it is important to accelerate the global deployment of vaccines to reduce virus transmission and remove opportunities for new variants. “
Professor Danny Altmann, Professor of Immunology at Imperial, said: “ At a time when the outlook generally improves in countries with substantial vaccine deployment programs, this study reminds us of the need to be vigilant about the threat of variants. Most people vaccinated in the UK received only one dose. While we know this offers remarkable protection against the original virus, our data suggests that it leaves people vulnerable to the variants of concern. “
Professor Áine McKnight, Queen Mary University, London, said: “Our study is reassuring and warning. We show that current vaccines offer some protection against the worrisome variants. However, people who received only the first course of a double-dose vaccine will show a more moderate immune response. We must ensure that the global immunization program is fully implemented. The current events in India painfully show the cost of complacency. “
Professor James Moon, University College London and Barts, said: “These findings represent the best of collaborative science between hospitals, universities and government agencies, providing important timely findings to inform policy and strategy . “
The study was carried out in collaboration with researchers from the Barts Health NHS Trust, Public Health England, the Royal Free Hospital NHS Trust, University College London and the University of Nottingham.
The research was supported by funding from the UKRI Medical Research Council, Rosetrees Trust and Barts Charity.