The immune system's T cells in those who had recovered from COVID-19 before the emergence of mutant forms of the novel coronavirus can still recognise virus versions from the UK, South Africa, and Brazil, according to a new study.

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In the research, published in the journal Open Forum Infectious Diseases, scientists analysed blood cell samples from 30 people who had recovered from the coronavirus infection before the emergence of variants. The researchers, including those from Johns Hopkins University School of Medicine in the US, found that one key player in the immune response to the novel coronavirus, called the CD8+ T cells, remained active against the virus, suggesting that current vaccines might offer some protection against variants via these cells.

Earlier studies had shown that some versions of the constantly evolving virus had changes in the region of its spike protein which enables it to attach to and enter cells, raising concerns that these mutations could make them less recognisable to the body's T cells and antibodies.

While details about the exact levels and composition of antibody and T-cell responses needed to achieve immunity to the coronavirus are still unknown, scientists assume that strong and broad responses from both antibodies and T cells are required to mount an effective immune response. In particular, studies had shown that CD8+ T cells limit infection by recognising parts of the virus protein presented on the surface of infected cells and killing those cells.

In the current study, the scientists found that SARS-CoV-2-specific CD8+ T-cell responses remained intact and could recognise "virtually all mutations in the variants studied". Based on the results, the scientists said the T-cell response in recovered COVID-19 patients, and most likely in vaccine recipients, are largely unaffected by the mutations found in the UK, South African and Brazilian variants, "and should offer protection against emerging variants".

However, they added that further research involving more participants is needed to validate the findings. The researchers call for larger studies to monitor the breadth, magnitude and durability of the anti-SARS-CoV-2 T-cell responses in recovered and vaccinated individuals to determine if booster vaccinations are needed.