In the past two and half years our health service has endured a global pandemic, staff shortages, terrible ambulance queues, long-waiting lists and a social care crisis; and we are now again seeing warnings of severe pressures in the NHS in the coming winter season. But the truth is that we are confronted by even more uncertainty than usual about the scale of “winter pressures” that we will face. The excess emergency admissions in a normal winter are largely driven by viral respiratory illnesses in the colder months, and the three prominent winter viruses that are a concern now are influenza, RSV (respiratory syncytial virus, a cold-like virus that can cause serious illness in some cases) and Covid-19. What we mean by “winter pressure” is large numbers of vulnerable people, particularly elderly people, getting one of these viral infections on top of pre-existing health conditions, or the frailty of old age, and ending up in hospital – so that the system grinds to a halt. We haven’t had any significant flu outbreaks for the past two winters (wonderfully absent as a side effect of Covid-19 restrictions) and so there is a real concern that it may be back with a vengeance now that we are back to more normal levels of social mingling: it came earlier than usual in the recent Australian winter and produced a sharp peak in cases. When flu comes to our shores this year, and we can be reasonably sure it will, vaccination of children (with the nasal vaccine) and of older adults could reduce its potential impact. But we are uncertain about what will actually happen: we can’t be sure exactly how the virus will behave in the northern hemisphere, we don’t know how many of those who are in need of a jab will come forward, and we don’t know whether or not the virus we get here will match our vaccine strain well and give the highest levels of protection to vaccine-recipients. So it could be bad, but it’s difficult to say how much pressure it will put on hospitals this year. RSV (respiratory syncytial virus) arrived unseasonably early here in the UK this year. In most years, this virus is fairly predictable, reaching a sharp peak in infections in November, but its behaviour has changed since lockdown and social distancing caused a dramatic reduction in population immunity. Fewer people got it in the past few years, so fewer people have immunity. There is now much more opportunity for its spread out of season. So, with this early transmission, RSV might be gone before the winter and not even in the mix. But it might also roll through the autumn and winter, and cause a more normal peak as the darker months arrive. Again, this adds uncertainty. As for the newest virus, we really just don’t know what will happen next with Covid-19. BA4/5 Omicron has largely had its day and is now in decline, so it is highly unlikely that these variants will be here for the winter – just as Alpha, Beta, Gamma and Delta all fizzled out after their appearances around the globe last year. Will the immense wall of immunity from all the vaccine doses and infections delay the next wave further into the future so that we are spared this winter? Or will a new Covid-19 variant emerge to add to a bad flu season and cause a deepening crisis? We simply don’t know. We can’t afford to get our approach wrong, and so the best way to prepare is to protect those at risk through vaccination. The NHS will be vaccinating older adults and those with health conditions against flu and Covid-19 in the weeks ahead. In addition, vaccinating children using the nasal flu vaccine will protect them and also reduce transmission of this virus to frail adults. We don’t yet have vaccines for RSV, but vaccines and monoclonal antibodies are in development and could be game-changing in future years. Because vaccines don’t reach everyone and can’t protect against all infections, there will always be some people who end up in hospital. This is expected, but the scale of these admissions this year is very hard to predict. There are also some immunocompromised individuals who can’t respond to vaccines: innovation in preventive therapies for this group must be a high priority. Monoclonal antibodies seem the most likely approach, but to be effective these need to match the virus strain that appears next, and we don’t know yet what that will be. While there is a lot of uncertainty about how badly these respiratory viruses will behave this winter, there is one certainty: if they do stack up together the NHS is not sufficiently resilient to deal with it. Whatever this winter brings, most experts think that Covid-19 will likely be added to the mix of RSV and flu in future normal years, and a rapidly expanding older population compounds these risks. The NHS will need more capacity to cope. A more resilient NHS would help in the winter, but, in the afterburn of Covid-19, we should not overlook the fact that resilience is also a core part of preparedness for future pandemics. Professor Sir Andrew Pollard was chief investigator of the Oxford Covid-19 vaccine trials and is director of the Oxford Vaccine Group