May 8, 2021

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A single COVID vaccine dose enhances protection against variants in previous infections: a study

A study shows that a single dose of the COVID-19 vaccine enhances protection against SARS-CoV-2 variants, but only in those previously infected with the disease. The researchers looked at the variants of the United Kingdom and South Africa, however, they believe that it is possible that the results apply to other common variables, such as the variants of Brazil (P.1) and India (B.1.617 and B.1.618).

The results, published in the journal Science, show that in those who have never been infected before and have only yet received a single dose of the vaccine, the immune response to the worrisome coronavirus variants may be insufficient.

Researchers at Imperial College London, Queen Mary University of London and University College London studied immune responses in UK healthcare workers at Barts Hospitals and Royal Free Hospitals after their first dose of the Pfizer / BioNTech vaccine.

They found that people who had previously experienced mild or asymptomatic infection significantly boosted protection against Kent and South African variants, after a single dose of mRNA vaccine.

In those who had never been infected with the COVID-19 virus, the immune response was less robust after the first dose, which could put them at risk for the variants.

“Our results show that people who received their first dose of vaccine, and who had not previously been infected with SARS-CoV-2, were not fully protected from the circulating variants of concern,” said Rosemary Boyton, professor of immunology and respiratory system. Medicine at Imperial College London, who led the research.

“This study highlights the importance of getting second doses of the vaccine that was introduced to protect the population,” Boyton said.

The researchers analyzed blood samples 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 African (B.1.351) variants of concern.

Besides antibodies, the researchers also focused on two types of white blood cells: B cells, which remember the virus, and T cells, which aid B cell memory and recognize and destroy cells infected with the Coronavirus.

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

However, in people without previous SARS-CoV-2 infection, a single dose of the vaccine decreased levels of antibody equivalent against SARS-CoV-2 and variants, rendering them susceptible to infection and highlighting the importance of the second vaccine dose.

It remains unclear precisely how much protection T cells provide.

Mutations in Kent and South African variants resulted in T-cell immunity that could be reduced, enhanced, or unchanged compared to the original strain, depending on the genetic differences between subjects.

“Our data show that normal infection alone may not provide adequate immunity against the variants,” Boyton said.

“Boosting with a single vaccine dose in people with a previous infection is likely to occur. As new variants continue to emerge, it is important to rapidly track global vaccine launches to reduce virus transmission and eliminate opportunities for new variants to emerge,” he said.