Scientists in the UK say a booster shot appears to offer good protection against the Omicron variant but two doses it not enough to stop you catching it.

An early analysis found receiving a third dose prevented about 75 per cent of people getting any COVID symptoms, the BBC reports.

Data from 581 Omicron cases and thousands of Delta cases was examined to determine the effectiveness of vaccines against the new variant.

The world is still trying to work out the full impact of Omicron and whether it could be a bigger problem than the Delta variant.

In India, which has detected 25 cases of Omicron, health officials have said all showed mild symptoms and the government had no immediate plan to authorise vaccine boosters.

Senior health official Vinod Kumar Paul told a news briefing that government experts were studying data on boosters but “our emphatic view… is to (first) cover every adult with (just) the primary two doses”.

The government has said this target could be achieved by January.

About 87 per cent of India’s adults, estimated at 939 million people, have received at least one dose of a vaccine and 54 per cent of them have received the full two.

In South Africa, booster doses of  Pfizer and Johnson & Johnson will be offered after 22,000 new virus cases were recorded in one day during the country’s fourth wave.

Health Minister Joe Phaahla said there were positive signs from early hospital data showing Omicron appears to be causing mainly mild infections.

Glenda Gray, president of the South African Medical Research Council, said there were far more unvaccinated people among current hospital admissions.

On the Pfizer vaccine, she said: “We are seeing this vaccine is maintaining effectiveness. It may be slightly reduced, but we are seeing effectiveness being maintained for hospital admissions and that is very encouraging.”

Meanwhile the World Health Organisation continues to oppose making booster shots against COVID-19 universally available, in the interests of making first jabs more accessible worldwide.

The WHO has expressed concerns that rich countries spooked by the emergence of the Omicron variant could step up the hoarding of COVID-19 vaccines.

The United Nations health agency, after a meeting of its expert panel on vaccination, reiterated its advice to governments against the widespread use of boosters in their populations so that well-stocked countries instead can send doses to low-income countries that have largely lacked access to them.

“What is going to shut down disease is for everybody who is especially at risk of disease to become vaccinated,” said Dr Kate O’Brien, head of the WHO’s department of immunisation, vaccines and biologicals.

“We seem to be taking our eye off that ball in countries.

“As we head into whatever the Omicron situation is going to be, there is risk that the global supply is again going to revert to high-income countries hoarding vaccine to protect – in a sense, in excess – their opportunity for vaccination, and a sort of ‘no-regrets’ kind of approach,” Dr O’Brien said.

“It’s not going to work,” she added.

“It’s not going to work from an epidemiological perspective and it’s not going to work from a transmission perspective unless we actually have vaccine going to all countries because where transmission continues, that’s where the variants are going to come from.”

-with AAP