A future variant of Covid-19 could be much more dangerous and cause far higher numbers of deaths and cases of serious illness than Omicron, leading UK scientists have warned. As a result, many of them say that caution needs to be taken in lifting the last Covid restrictions in England, as Boris Johnson plans to do next week. At the same time, demands are growing for Chris Whitty and Patrick Vallance, the government’s most senior advisers on Covid, to hold a press conference to reveal what evidence there was to back the decision to end all pandemic restrictions. The dangers posed by accepting the widespread assumption that Covid-19 variants would continue to get milder in their impact was highlighted by epidemiologist Prof Mark Woolhouse, of Edinburgh University. “The Omicron variant did not come from the Delta variant. It came from a completely different part of the virus’s family tree. And since we don’t know where in the virus’s family tree a new variant is going to come from, we cannot knoW how pathogenic it might be. It could be less pathogenic but it could, just as easily, be more pathogenic,” he said. This point was backed by virologist Prof Lawrence Young of Warwick University. “People seem to think there has been a linear evolution of the virus from Alpha to Beta to Delta to Omicron,” he told the Observer. “But that is simply not the case. The idea that virus variants will continue to get milder is wrong. A new one could turn out to be even more pathogenic than the Delta variant, for example.” David Nabarro, a special envoy on Covid-19 for the World Health Organization, also highlighted the uncertainty of how future variants might behave: “There will be more variants after Omicron and if they are more transmissible they will dominate. In addition, they may cause different patterns of illness, in other words they may turn out to be more lethal or have more long-term consequences.” Nabarro urged authorities to continue to plan for the possibility that there will be surges in numbers of people who are ill and need hospital care. “It would be prudent to encourage people to protect themselves and others consistently. An approach that does not do this would be a gamble with potentially severe consequences. I cannot see any upsides to such a gamble. The pandemic has a long way to go and – as is the case since it started – people and their leaders will influence its long-term impact through actions they take now.” The warnings came as charities and teachers called for England’s chief medical officer and chief scientific adviser to offer a public explanation of the plan, unveiled in parliament last week, to lift all Covid restrictions – including the requirement to isolate after testing positive – in England from Thursday 24 February. The call comes as new figures suggest that people with blood cancer are now accounting for a higher proportion of Covid deaths than at any point in the pandemic. According to analysis by the Office for National Statistics, a total of 458 people with blood cancer in England and Wales died of Covid between October and December 2021 – one in 20 of those who died of Covid during that time. People with blood cancer have weakened immune systems and so are less likely to be protected by vaccines. “The lack of any joined-up plan to support the immunocompromised suggests that they have not featured prominently in the government’s decision to lift the remaining Covid restrictions,” said Gemma Peters, chief executive of Blood Cancer UK. “We understand we cannot keep restrictions for ever, but given the potential negative impact for immunocompromised people, it is important that the government’s advisers set out the scientific basis.” Fiona Loud, policy director of Kidney Care UK, urged the government to show commitment to the nation’s 500,000 immunosuppressed people by sharing their plans, and evidence for their decision-making: “Abandoning all measures without preventive treatments, free testing, and a duty not to expose immunosuppressed people to Covid-19 unnecessarily risks making us into second-class citizens.” Robin Bevan, headteacher of Southend high school for boys, said last week’s announcement felt premature: “It would be much more reassuring – and also be much easier to explain to parents and to pupils – if there was a narrative rooted in science rather than a narrative rooted in libertarian aspiration.” Ceinwen Giles, who has reduced immunity after cancer treatment, said Johnson’s announcement left her feeling excluded. “There seems to be the perception that somehow immunocompromised people are very old and very sick and it doesn’t really matter. If you are old and sick, you still matter. This just means we’re being shut out.” A government spokesperson said: “Those considered clinically extremely vulnerable are advised to follow the same guidance as the general public, but consider taking extra precautions to reduce their chance of catching Covid-19. Vaccines are the best way we can protect ourselves from the virus.”