A third top-up booster dose of a COVID-19 vaccine provides high levels of protection against severe disease from the Omicron variant among older adults, a latest UK study concluded on Saturday.

The UK Health Security Agency (UKHSA) analysis showed that around three months after the third jab, protection against hospitalisation among those aged 65 and over remains at about 90 per cent.

Whilst with a booster shot, the duration of protection against severe disease remains high, protection against mild symptomatic infection is more short-lived and drops to around 30 per cent by about three months.

The UKHSA study examined booster shots in those aged over 65, who were among the first to be eligible when the UK's booster vaccination rollout began in mid-September 2021.

The latest findings also show that protection from getting severe infection from the Omicron variant of COVID-19 after the first two doses wanes within months.

"With just two vaccine doses, protection against severe infection drops to around 70 per cent after three months and to 50 per cent after six months," the study noted.

The UK's Joint Committee on Vaccination and Immunisation (JCVI) said it has taken this latest evidence into account in its ongoing review of the booster programme and decided against the need for a fourth booster dose rollout at this stage.

"The current data shows the booster dose is continuing to provide high levels of protection against severe infections, even for the most vulnerable older age groups. 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," said Professor Wei Shen Lim, the JCVI's chair of COVID-19 immunisation.

"The data is highly encouraging and emphasises the value of a booster jab. 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," he said.

The JCVI has concluded that there is no immediate need to introduce a fourth jab to the most vulnerable groups such as care home residents and those aged over 80 and that priority should continue to be given to rolling out the first booster shots to all age groups.

However, extremely vulnerable patients with impaired immune systems are still advised to administer the fourth shot to get fully vaccinated.

More than 35 million boosters and third doses have now been administered across the UK, with the government's "Get Boosted Now" campaign at the end of last year to tackle the surge in coronavirus cases driven by the Omicron variant.

It comes at a time when the UK's daily infections rate continues to remain high, with another 178,250 cases being reported on Friday.

Hospitalisations, which have remained relatively low, have also started to rise among the vulnerable age groups.

As a result, the widespread staff absences due to self-isolation have caused severe pressures on the country's National Health Service (NHS), with Army personnel being drafted in for support in some regions.

"I think we have to be honest when we look at the NHS and say it will be a rocky few weeks ahead," said UK Health Secretary Sajid Javid.

About 4 per cent of hospital staff in England - nearly 36,000 - were off work for reasons related to COVID-19 during the week ending January 2. When other sickness absence is added, it brings the total to 9 per cent - nearly double what would normally be seen at this time of the year.