Sage advisers cautioned that a “very stringent response” from Downing Street may be needed, while scientists in the New and Emerging Respiratory Virus Threats Advisory Group (Nervtag) said a spike in cases could overwhelm the NHS.
The warnings emerged as nine new cases of the more transmissible omicron variant were identified in England, bringing the total to 22.
Boris Johnson has clashed with health officials and independent scientists about the level of restrictions in place, with the prime minister insisting that the measures introduced this week – mandatory masks in shops and public transport, and more stringent checks on travellers – will be enough to curb cases and keep the new variant at bay.
However, the World Health Organisation (WHO) warned that travel bans will not stop the international spread of omicron, while health secretary Sajid Javid admitted that cases of the variant will continue to rise in the UK.
A total of 48,374 Covid infections were reported on Wednesday, alongside 171 fatalities, bringing the UK’s death toll to 169,020.
Cases also remain high in Europe, with politicians on the continent poised to debate making Covid vaccinations mandatory due to low vaccination rates across the 27-nation bloc. “It is understandable and appropriate to lead this discussion now,” said European Commission president Ursula von der Leyen, adding that 150 million Europeans are unvaccinated.
Clearer information on the transmissibility of omicron is meanwhile expected “within days,” according to the WHO. The government’s own Sage advisers, in minutes leaked to the BBC, noted that it is too early to determine the severity of disease caused by the variant or jump to firm conclusions due to data limitations.
However, meeting on 29 November, the scientists said that “any significant reduction in protection against infection could still result in a very large wave of infections. This would in turn lead to a potentially high number of hospitalisations even with protection against severe disease being less affected.
“It is important to be prepared for a potentially very significant wave of infections with associated hospitalisations now, ahead of data being available.”
Nervtag, which is a sub-group of Sage, echoed similar warnings during an “extraordinary meeting” it held on 25 November. “We cannot exclude that this wave would be of a magnitude similar, or even larger, than previous waves,” the advisers stated in minutes that surfaced on Wednesday.
In the eventuality of such an outcome, this surge in infections “will be accompanied by a wave of severe cases, and the subgroup cannot rule out that this may be sufficient to overwhelm NHS capacity,” Nervtag added.
The experts similarly called for “early and robust actions” to limit the spread of the variant in the UK. They did not specify measures, but reiterated the need for Britain’s vaccine programme to be accelerated. The PM said on Tuesday the government is aiming to have offered all adults a booster by the end of January.
For now, scientists are racing to better understand the transmissibility of omicron, its lethality and its ability to evade immunity acquired via injection or infection.
The WHO said early indications suggest cases caused by the variant are “mild”, adding that there is no evidence to suggest the effectiveness of the vaccines has been reduced by omicron – yet the body failed to provide any data to support its assertions.
Paul Hunter, a professor of health protection at the University of East Anglia, said it is “far too soon to be certain” about such claims.
If immunity levels in the population are insufficient in providing protection, omicron “could rapidly spread throughout the UK and we could see serious increases in hospitalisations,” Prof Hunter said.
“On the other hand, if it spreads less rapidly and existing immunity is sufficient to still reduce risk of severe disease it may have only a relatively small impact of health care provision. We just don’t know as yet.”
Although the government’s top scientists remain unsure how big a wave of omicron infection might be, Sage advisers warned that a “very stringent response measures” could be needed from Downing Street.
During the 29 November meeting, the experts noted that pre-departure Covid testing for travellers returning to the UK would be “valuable”. The current policy of a single PCR test within two days of arrival will “identify significantly fewer cases” than an additional test on either day five or day eight, they add.
No 10 said ministers make “balanced” judgements on the scientific advice it receives. Asked if the government had ignored the guidance, the prime minister’s official spokesperson said: “At all times we take account of any clinical advice we receive, and then we need to make a balanced judgement on what is right.”
Labour said the lack of pre-departure testing for those flying to the UK from abroad was an “obvious gap in the country’s defences” against the omicron variant – demanding “strong action at the border now”.
No 10 was also challenged on whether it was now government policy that partygoers take a lateral flow test before events, after health secretary Sajid Javid suggested that people could take a test before attending parties.
The PM’s official spokesperson said: “I think he was very clear about what he was saying. He was setting out that we do have a significant testing capacity, and if people wanted further reassurance they could use that.”
Omicron has been reported in 23 countries, according to the WHO. “We expect to have more information on transmission within days, not necessarily weeks, but in days,” said Dr Maria Van Kerkhove, Covid-19 technical lead of the WHO.