The chance of testing positive for Covid after being double jabbed rises by nearly 60 per cent in the months following vaccination, with experts saying boosters are needed to keep immunity high.

The latest data from Imperial College’s React survey, which monitors community infection levels, found prevalence among fully vaccinated people in the three months after their second jab was around one in 285 – 0.35 per cent.

However, between three and six months it rose to one in 181, a 57 per cent increase. The risk is still far less than for unvaccinated people, among  1.76 per cent, or one in 56, were found to have the virus.

Prof Paul Elliott, the director of the React programme, said: “The positivity rate for two doses within six months is higher than that for less than three months.

“So there’s some suggestion that maybe there is a higher rate of breakthrough infection after three months and we can’t really say what happens after that. It definitely shows incentive for people to get their booster when it becomes available.”