Single COVID vaccine dose boosts protection against variants in previously infected: Study

A single dose of COVID-19 vaccine boosts protection against SARS-CoV-2 coronavirus variants, but only in those previously infected with the disease, according to a study.

The researchers looked at the UK and South Africa variants, 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.

The findings, published in the journal Science, show that in those who have not previously been infected and have so far only received one dose of vaccine, the immune response to coronavirus variants of concern may be insufficient.

The researchers at Imperial College London, Queen Mary University of London and University College London, looked at immune responses in UK healthcare workers at Barts and Royal Free hospitals following their first dose of the Pfizer/BioNTech vaccine.

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.

"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," said Rosemary Boyton, Professor of Immunology and Respiratory Medicine at Imperial College London, who led the research.

"This study highlights the importance of getting second doses of the vaccine rolled out to protect the population," Boyton said.

The researchers analysed the 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 Africa (B.1.351) variants of concern.

Along with antibodies, 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.

They found that after a first dose of vaccine, prior infection was associated with a boosted T cell, B cell and neutralising 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.

It remains unclear precisely how much protection is offered by T cells.

The mutations in the Kent and South Africa variants resulted in T cell immunity which could be reduced, enhanced or unchanged compared to the original strain, depending on genetic differences between people.

"Our data show that natural infection alone may not provide sufficient immunity against the variants," Boyton said.

"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," she said.