Immunity to coronavirus could be lost within months of contracting the killer bug, which may return each year like common colds, a UK study claims.
King's College London scientists found levels of antibodies - the body's main line of defence - were at their highest around three weeks after symptoms arose but quickly decline.
That suggests any potential vaccine may follow the same pattern and require annual boosting immunisations, while the idea of 'herd immunity' could be unlikely to work.
Sixty per cent of the close to 90 patients and healthcare workers at Guy's and St Thomas' NHS foundation trust - which treated Boris Johnson - involved in the research had a "potent" antibody response at the peak of their battle.
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But within three weeks blood tests revealed only 17 per cent of them had retained the same levels, which had fallen as much as 23-fold - some becoming undetectable.
Dr Katie Doores, lead author of the 'Longitudinal evaluation and decline of antibody responses in SARS-CoV-2 infection', told the Guardian vaccines may show the same rapid decline.
"People are producing a reasonable antibody response to the virus, but it’s waning over a short period of time and depending on how high your peak is, that determines how long the antibodies are staying around," she said.
"Infection tends to give you the best-case scenario for an antibody response, so if your infection is giving you antibody levels that wane in two to three months, the vaccine will potentially do the same thing,” said Dr Doores.
"People may need boosting and one shot might not be sufficient."
The study - which has not yet been peer-reviewed - is the first to have monitored antibody levels for three months after symptoms emerged.
Prof Jonathan Heeney, a virologist at the University of Cambridge, said the study "puts another nail in the coffin of the dangerous concept of herd immunity".
Speaking on Sky News, meanwhile, Professor Robin Shattock, of Imperial College London, said there is "no certainty" any of the dozens of vaccines being developed would necessarily work.
However, he added it is likely if someone was re-infected the virus would be "less severe" due to immune memory - but they could still pass it on to others just as easily.
