Analysis by the UK Health Security Agency (UKHSA) found over-65s who had a third jab three months before still had 90 percent protection against hospitalisation.
It suggests that immunity is not waning as quickly as it did three months after a second vaccine dose.
So those among the first to have a booster jab in September do not need a second round at this time.
However, the Joint Committee on Vaccination and Immunisation (JCVI) said the decision will be kept under review.
Experts added that it was more vital to continue rolling out first, second and booster shots to all age groups.
Professor Wei Shen Lim, the JCVI’s chair of Covid-19 immunisation, said: “The current data shows the booster dose is continuing to provide high levels of protection against severe disease, even for the most vulnerable older age groups. The committee has concluded there is no immediate need to introduce a second booster dose, though this will continue to be reviewed. The data is highly encouraging and emphasises the value of a booster jab.”
The JCVI also noted that the Omicron wave was progressing very swiftly, so giving more doses to those already well protected would be unlikely to have much impact.
Prof Lim added: “With Omicron continuing to spread widely, I encourage everyone to come forward for their booster dose or, if unvaccinated, for their first two doses, to increase their protection against serious illness.”
With just two vaccine doses, protection against severe disease drops to around 70 percent after three months and to 50 percent after six months.
Protection against severe disease remains high for longer after a booster but immunity to mild infection is more short lived, dropping to around 30 percent three months after a third inoculation.