Boris Johnson’s decision to remove all plan B measures in England – and to signal the end of the legal requirement to self-isolate – comes as the Omicron surge in the UK appears to have peaked. The move means compulsory mask wearing in shops and on public transport, guidance to work from home and vaccine certificates will be scrapped in England next week, with the need to self-isolate lapsing on 24 March if not before. What impact will this have on the epidemic? One question scientists have yet to nail is the extent to which different factors are driving infections down. High levels of immunity due to vaccines, boosters and runaway infections play a big role, but that protection is more effective against hospitalisation and death than against catching the virus. Another major force that has shaped the Omicron wave is people’s behaviour, which extends far beyond plan B. Monitoring by the London School of Hygiene & Tropical Medicine (LSHTM) showed this week that people reduced their contacts throughout the autumn and have kept them low in December and January, with adults reporting fewer than three contacts a day. There is plenty of room for socialising, and infections, to bound back. Many epidemiologists expect infections will pick up again in England. Modelling from the University of Warwick suggests that such a rise could drive an “exit wave” of hospitalisations in April and May. Admissions are unlikely to reach the levels hit this winter, but one concern is that the rise in cases could coincide with waning booster immunity in older and more vulnerable people. Hospitalisations are not the only issue: there is still huge uncertainty around how much Omicron will increase the prevalence of long Covid. Behaviour has helped Omicron peak in other ways, too. In the run-up to Christmas, routine lateral flow testing became widespread and a large proportion of reported cases were detected that way. If people interpret falling cases as the end of the crisis – and scrapping the legal requirement for self-isolation might encourage that view – they may pose a greater risk to others. “I suspect this has been one of the most important contributors to the Omicron wave being smaller than predicted,” said Prof Mark Woolhouse, an infectious disease epidemiologist at Edinburgh University. “This is particularly important for anyone planning a contact with a vulnerable person and will remain so for the foreseeable future, in my view.” While cases are falling at the UK level, the picture is mixed nationally and regionally. It is unclear whether infections are falling in Northern Ireland, or in north-east and south-west England, for example. Going into the spring, more fine-grained data is going to be crucial to reveal whether Omicron is holding on, or has begun to rise again, in particular areas. “We shouldn’t be looking at averages any more,” said Martin McKee, a professor of European public health at LSHTM and a member of the Independent Sage group. “There are still a hell of a lot of people not vaccinated in the UK. There are parts of the country where a lot of people are living in very difficult circumstances, with overcrowding and all the conditions where the virus spreads, and I am very worried about that.” How Covid persists in different age groups will also be important to monitor. As of last week, infections were falling in all age groups in England except children aged two to 11 – the unvaccinated young – prompting concerns about Covid in schools. Boris Johnson’s announcement means that from Thursday staff and pupils in schools in England will not be required to wear masks in classrooms. They will continue to wear them in communal areas until next Thursday, and where there are significant outbreaks public health directors can recommend a return to face masks. Face coverings have been a source of growing dispute in schools, as heads have struggled to enforce the latest government advice. Many school leaders will be glad to see them go but there is concern in the sector that the announcement is premature with cases still high in some areas. “Removing measures such as masks in schools is crazy,” said Prof Stephen Reicher, a behavioural scientist at the University of St Andrews who advises Sage and Independent Sage. “This has much more to do with appeasing those who might otherwise be writing to the 1922 Committee [to try to oust the prime minister].” Behavioural scientists have shown throughout the crisis, and in previous pandemics, that people act according to the risk they perceive. Telling people they will no longer have to self-isolate sends a message that “it’s all over”, said Reicher. “This will impact all behaviours including – critically – the need to get vaccinated and boosted. The government’s approach will undermine even the steps they still acknowledge are important.”