Britain’s wave of Omicron infections could reach 1m a day by the end of December, the government’s most senior public health adviser has warned amid growing calls to limit Christmas gatherings. Dr Susan Hopkins told MPs on Tuesday the Omicron Covid variant was initially doubling every two to three days in the UK but the pace appeared to have speeded up, driving a surge of disease that risked putting “significant” pressure on the NHS. While confirmed cases of the variant are being tracked through genomic testing, the number of Omicron infections across the country is estimated to be far higher – at an estimated 200,000 daily infections on Monday – due to a time lag and because many cases are never picked up by the testing programme. Hopkins said with so many people expected to contract the virus over the coming weeks, the NHS would come under significant pressure if only a fraction became ill enough to need hospital care. “If we have a million infections a day, even a very small proportion of those individuals requiring hospitalisation will put a significant impact on healthcare,” she told the Commons science and technology committee. There are also concerns about the impact on schools, lorry drivers and shop workers if cases continue to rise rapidly while forcing 10 days’ isolation for anyone who contracts Covid. The warning came as Nicola Sturgeon urged Scots to limit indoor mixing to no more than three households over Christmas and reduce social contacts “as much as possible” in the coming weeks to help slow the spread of the variant. The first minister stressed the restrictions were not a legal requirement and family festive celebrations could go ahead, but said: “We are asking everyone – and we will issue strong guidance to this effect – to cut down as far as possible the number of people outside our own households that we are interacting with just now.” Ahead of MPs voting in the Commons on “plan B” measures, including the requirement for either proof of two vaccine doses or a negative lateral flow test (LFT) to enter some public venues, Hopkins said people should take an LFT beforehand regardless of their jab status. “We’ve advised that the optimal is being vaccinated and that we also recommend people have [LFTs] before they go,” she told MPs. “While certification will talk about vaccine or [LFTs], our strong public health recommendation is that if people are going out to venues to socialise, they should do a lateral flow test before they go to reduce the risk of going into that venue with asymptomatic infection and therefore transmitting to others.” Some restrictions to slow the spread of Omicron would probably be needed for the next four to eight weeks, she said. Speaking at a meeting of the all-party parliamentary group on coronavirus, Prof Wendy Barclay, a member of Sage and a virologist at Imperial College London, said it was too soon to know the severity of disease caused by Omicron. Hospitalisations are rising fast in South Africa, where the variant was first spotted, and while there are reports of hospital stays being short and that intensive care occupancy may be lower, the younger population in South Africa and previous waves of infection there make comparisons with the UK difficult, according to Barclay. New data from the insurer Discovery Health together with the South African Medical Research Council shows protection against severe complications following two jabs is about 70% for Omicron compared with 90-95% for Delta. “That suggests that even for severe disease, there is probably a fall-off in the vaccine protection against Omicron,” Barclay said. Prof Christina Pagel, the director of the clinical operational research unit at University College London (UCL), said early data from Denmark suggested similar proportions of confirmed cases were resulting in hospital admissions with Omicron as with Delta. Stephen Reicher, a member of the Sage subcommittee advising the government on behavioural science and a professor of psychology at the University of St Andrews, warned it would take several weeks to roll out booster jabs and another fortnight before they took effect. “If we were to do nothing now, by then the cases would be catastrophically high. So we need to bring cases down in order to give us time to vaccinate,” he said. “There are two ways you can bring them down. You can bring them down by giving very clear advice, which is don’t socialise. If you do socialise now you won’t be able to socialise at Christmas.” The alternative, he said, was that socialisation could be limited by legislation. “Now, that’s a very real debate. But it seems to me that’s the only debate that should be being had right now, not whether but how we bring down the level of contact.” Hospitals in England are bracing themselves for a “significant” surge in Covid patients from next week because the Omicron variant is spreading so fast, a senior NHS leader said. Omicron’s greater transmissibility means hospitals would again have to treat large numbers of patients despite it apparently inducing milder symptoms than the previously dominant Delta variant, said Chris Hopson, the chief executive of NHS Providers. On Tuesday, the UK’s four chief medical officers approved a temporary suspension of the 15-minute observation period to help speed up the vaccine rollout. Patients normally stay at the vaccination centre for a short time after having their shot in case they experience a serious allergic reaction, which happens with about one in 100,000 doses. The observation period will remain in place for people who have previously experienced anaphylaxis or other allergic reactions.