Around three months after receiving a third jab, protection against hospitalisation among those aged 65 and over remained at about 90%, the UK Health Security Agency said.
"The data is highly encouraging and emphasises the value of a booster jab," Wei Shen Lim, chair for COVID-19 immunisation on the government's Joint Committee on Vaccination and Immunisation, said in a statement.
By comparison, with only two vaccine doses, protection against severe disease for the over-65s dropped to around 70% after three months and to 50% after six months, the UKHSA said.
"The current data show the booster dose is continuing to provide high levels of protection against severe disease, even for the most vulnerable older age groups," Lim said.
"For this reason, the committee has concluded there is no immediate need to introduce a second booster dose, though this will continue to be reviewed."
Protection against mild symptomatic infection was more short-lived than against severe disease and dropped to around 30% after about three months, the UKHSA said.
Israel is now administering fourth doses to people over 60 and health workers, as well as immunocompromised patients, after finding they boost antibodies five-fold within a week.
