A single dose of COVID-19 vaccine boosts protection against the infection only for those who have been previously infected, PTI reported, referring to a study. It noted that the estimation proved to be true currently for only the UK and South Africa variants, but could apply to other variants also, such as the Brazil (P.1) and India (B.1.617 and B.1.618) strains.

The findings have been published in the journal Science, and show that those who have not been infected yet and have received a shot of vaccine, might be developing an immune response insufficient to fight against different variants.

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Immune Responses were observed in UK healthcare workers at Barts and Royal Free hospitals after their first dose of the Pfizer/BioNTech vaccine, by researchers from Imperial College London, Queen Mary University of London, and University College London.

The researchers reportedly found out that those who had previous cases of mild or asymptomatic infection had developed protection against the UK and South Africa variants after one shot of the vaccine.

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"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," Rosemary Boyton, Professor of Immunology and Respiratory Medicine in Imperial College London, was quoted as saying.

Blood samples were analysed for immunity levels against various strains, including both UK, South Africa as well as the original SARS-CoV-2 coronavirus strain.