Two Covid vaccine doses become less effective at stopping infections within six months, a major study has found.
Researchers warned Britons given the jabs first including the elderly could see protection plummet to just 50 per cent by winter without boosters.
The real-world study, led by Kings College London, looked at more than a million people who had been fully vaccinated.
Its unclear whether the waning immunity against infection also means people are less protected against hospitalisation and death.
But Professor Tim Spector, the lead scientist behind the study, said high levels of infection would ultimately lead to more deaths. He warned effectiveness could drop below 50 per cent by winter, and urged Britain to urgently get its act together on booster vaccines.
It comes on the back of a separate study last night which found four in 10 people who have weakened immune systems show low or undetectable levels of Covid immunity after being double vaccinated.
Both studies will pile pressure on the Governments scientific advisers to green light a booster jab programme for the elderly and vulnerable this autumn.
The Joint Committee on Vaccination and Immunisation (JCVI) is expected to approve booster doses for the immunocompromised in the coming weeks.
But Professor Adam Finn, who sits on the JCVI, suggested this morning the group will stop short of recommending them for healthy elderly adults until more evidence of the benefit surfaces.