England’s chief medical officer has warned of a “disastrous” resurgence in coronavirus cases if people stop adhering to social distancing guidelines now that the mass vaccination programme has begun. Prof Chris Whitty told MPs that the winter months were high risk for the NHS, particularly because of respiratory infections. He stressed the importance of immunising an estimated 20 million people made a priority for a jab before any substantial easing of restrictions. He told a joint hearing of the Commons committees for science and technology and health and social care that the UK was heading into spring 2021 “in much better shape than three or four months ago”, but he warned against complacency. “That would be disastrous, because then actually the wave would come back incredibly quickly. We’re all very nervous about January and February, which is the highest risk period for the NHS in particular, March as well. The alternative is to say actually there is an end to this, we just need to get ourselves through this last period, and we really must be self-disciplined, as we have been all the way through this year.” This week some of the most vulnerable people in the UK received the first shots of the Pfizer/BioNTech vaccine outside a clinical trial, as the NHS began the most ambitious mass vaccination programme in its history. Older people in care homes, other people over 80 and health and care workers are first in line for the vaccine, followed by people with health conditions and younger people. Despite vaccines being “by far the strongest tool in our box”, said Whitty, very few people would recommend “starting to really remove [restrictions] during a high-risk period of the year, which the winter always will be for respiratory infections, until you have got covered the tiers which the Joint Committee on Vaccination and Immunisation (JCVI) has laid out.” He added: “I want to be very clear. For the next three months we will not have sufficient protection. The idea we can suddenly stop now because the vaccine is here – that would be really premature, it’s like someone giving up a marathon race at mile 16. It would be absolutely the wrong thing to do.” An estimated 20 million people are included in the JCVI’s priority list for the Covid-19 vaccine, which includes everyone aged 50 and over, and anyone from age 16 upwards who has a health problem that puts them at serious risk from coronavirus. The UK’s Medicines and Healthcare products Regulatory Agency (MHRA) approved the Pfizer/BioNTech vaccine last week and is reviewing clinical trials data for the AstraZeneca/Oxford University vaccine and the US National Institutes of Health/Moderna vaccine. Giving evidence to the session, June Raine, the chief executive of the MHRA, said the regulator expected a further package of trial data from AstraZeneca in the coming days, which would inform its decision on granting a licence for emergency use. Further data from trials of the US Moderna vaccine are expected in the next week or two. Whitty said he expected to have a portfolio of three to four vaccines by the middle of next year. Clinical trials of the Pfizer, AstraZeneca and Moderna vaccines showed they helped to protect against severe Covid-19 disease, but it is less clear whether they prevent infections entirely and stop people spreading the virus. Whitty said the short-term impact of the vaccination programme would be to reduce hospitalisations and deaths. The virus would still circulate, however, leaving many people at risk of “long Covid”, a mix of medical problems that persist months after a person has seemingly recovered. On the prospects of returning to a near normal life, Whitty said that at some point society, through political leaders, would say the level of risk from the infection was tolerable, “just as we accept that in an average year 7,000 people die of flu, and in a bad flu year 20,000 people die of flu”. He added: “At a certain point you say actually the risk is now low enough that we can largely do away with certainly the most onerous things we have to deal with. This will be a kind of gradual retreat. But it is a de-risking process, rather than it’s just going to go away.”