The coronavirus pandemic that has so far killed more than 5 million people worldwide is far from over and the next one could be even more lethal, the creator of the Oxford/AstraZeneca vaccine has said.

As fears grow over the threat posed by the highly mutated Omicron variant, detected in more than 30 countries, Prof Dame Sarah Gilbert cautioned that while it was increasingly obvious that “this pandemic is not done with us”, the next one could be worse.

The message came as ministers were told by one of their scientific advisers that the new variant was spreading pretty rapidly in the UK, and travel rules starting on Tuesday would be too late to prevent a potential wave of infections. The UK Health Security Agency (UKHSA) on Sunday night reported 86 new Omicron cases, taking the total identified so far to 246.

Delivering the 44^th Richard Dimbleby lecture, due to be broadcast on the BBC on Monday, Gilbert said that despite the destructive nature of a two-year pandemic that had already infected more than 265 million people, the next one might be more contagious and claim even more lives.

“This will not be the last time a virus threatens our lives and our livelihoods,” she said. “The truth is, the next one could be worse. It could be more contagious, or more lethal, or both.”

Gilbert, a professor of vaccinology at the University of Oxford whose team developed the Covid vaccine now used in 170 countries, said the scientific advances made and knowledge gained in research fighting against the coronavirus must not be lost.

“We cannot allow a situation where we have gone through all we have gone through, and then find that the enormous economic losses we have sustained mean that there is still no funding for pandemic preparedness,” she said. “Just as we invest in armed forces and intelligence and diplomacy to defend against wars, we must invest in people, research, manufacturing and institutions to defend against pandemics.”

Gilbert said the new variant contained mutations already known to increase transmissibility of the virus and that antibodies induced by vaccination or previous infections might be less effective at preventing infection with Omicron. But she also said reduced protection against infection “does not necessarily mean reduced protection against severe disease and death”. Gilbert added: “Until we know more, we should be cautious, and take steps to slow down the spread of this new variant.”

From Tuesday, all passengers arriving in the UK will be required to show proof of a negative PCR or lateral flow test taken no earlier than 48 hours before departure. Nigeria will also be added to the travel red list on Monday.

But Prof Mark Woolhouse, of the Scientific Pandemic Influenza Group on Modelling (Spi-M), said the new travel rules were too late to make a material difference. He told BBC One’s The Andrew Marr Show: “I think that may be a case of shutting the stable door after the horse has bolted.

“If Omicron is here in the UK, and it certainly is, if there’s community transmission in the UK, and it certainly looks that way, then it’s that community transmission that will drive a next wave. The cases that are being imported are important, we want to detect those and isolate any positive cases we find, as we would for any case anywhere. But I think it’s too late to make a material difference to the course of the Omicron wave if we’re going to have one.”

Though the emergence of the new variant has caused alarm worldwide, Dr Anthony Fauci, the top US infectious disease official, told CNN “thus far it does not look like there’s a great degree of severity to it” but he added that it was too early to draw definitive conclusions and more study was needed.

As of 9am on Sunday there were another 43,992 lab-confirmed Covid-19 cases in the UK. A further 54 people died within 28 days of testing positive for coronavirus.

The president of the Royal College of Emergency Medicine said the NHS would be in a difficult position if the Omicron variant were to trigger a surge in hospital admissions. Dr Katherine Henderson said hospitals were already struggling to cope. “It is pretty spectacularly bad now, it will get worse – and if the new variant becomes a thing in terms of numbers and translates into hospitals admissions we are going to be in a very, very difficult position.”

The government is expected to announce the chair of its long-awaited Covid public inquiry within the next fortnight, having pledged to bereaved families that a chair would be in place by Christmas. MPs have called for the inquiry to investigate the effect that rule-breaking by public figures had on public compliance.

Meanwhile, Keir Starmer has made his strongest intervention to date to criticise those resisting taking the vaccine, after the Guardian reported that unvaccinated patients are dominating ICU beds.

The Labour leader, who will receive his booster jab on Monday, said those who are unvaccinated should “consider the impact of their decision, think again, and get vaccinated”.

“It is frustrating and worrying that medics are seeing too many hospital beds and NHS resources are taken by those that have chosen not to get the vaccine,” he said.

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He also said the government needed to radically boost efforts to get third jabs into arms. New analysis by Labour reveals the total number of booster vaccinations currently being administered remains significantly below the number of jabs that were being delivered at the same point in the first vaccine rollout earlier this year.

During the initial vaccine rollout, the number of vaccinations peaked at 602,265 a day on average. In contrast, the current total number of vaccines now being delivered a day on average is 435,542, over a quarter less than in March.

Separately, millions of people are being urged to get a flu jab by Friday to maximise protection over Christmas, as figures reveal more than half of all those who are pregnant or have underlying health conditions have still not been vaccinated. The UKHSA is encouraging eligible people to have the vaccine by 10 December to allow it take full effect before the festive season.

Andrew Gregory and Jessica Elgot