Immunity to coronavirus lasts at least eight months and may even continue for years, new research has suggested.
Scientists looked at immune cells in survivors of Covid-19, including those that store “memory” of the virus which can activate antibodies.
The study, led by scientists at La Jolla Institute for Immunology at San Diego university in the US, assessed elements of the immune response including antibodies and T-cells, and found the “immune memory” may last for at least eight months.
Experts said the slow rate of decline in some of the cells required for immunity could mean it lasted even longer.
The study has raised hopes that the protection conferred by coronavirus vaccines could last for years, and that an annual jab may not be required.
A number of recent papers have suggested immunity may wane in as little as three months, raising questions over the effectiveness of a vaccine.
But newer recent research on T-cells was more optimistic, suggesting a response could last for much longer.
However, scientists said the new study findings indicated that it was possible the “immune memory” could
still be triggered many years later.
In the study, posted ahead of peer review on medRxiv, a health science website, researchers took periodic measurements of the levels
of antibodies as well as memory T- and B-cells, and other immune cells in the body.
The T-cells – the immune component that both kills off infected cells and helps B-cells make antibodies – were found to still be present at six months.
Scientists had feared that those who developed only mild infections would be unlikely to have a strong immune response, but almost all developed cells capable of creating new antibodies if they encountered the virus again.
Stephen Evans, professor of pharmacoepidemiology at the London School of Hygiene and Tropical Medicine, said it was probably “good news for vaccines being able to provide immunity that is more than very short-term”.