here has not been a lot of good news lately. But with the discharge of Boris Johnson from hospital on Sunday, and statements that the “peak” strain on the National Health Service would be over the Easter period, you might be under the impression that the storm is passing, and the Covid-19 pandemic will soon be a memory. Fueling this mood are reports from studies of communities already hit by the pandemic. At long last we are beginning to see the results of work looking for signs that people have already been infected, through the presence of antibodies against Sars-CoV-2, the virus which causes Covid-19. Some of this data suggests strongly that many infections may have passed unnoticed, with the only symptoms being mild things such as loss of the ability to smell and taste, and that as a result, more people may be immune than had been thought. Surely this is a sign that communities around the world can breathe a sigh of relief and start getting back to work? Unfortunately, it is nothing of the kind. Talk of the “peak” can be misleading, because it’s not clear whether you are talking about the Matterhorn or Table Mountain – both have a summit, but the peak is far more pronounced in one than the other. In countries such as Italy (unlike Wuhan) the initial surge in the Covid-19 pandemic has not evaporated quickly. There are multiple reasons for this but the most important is that the impact of physical distancing achieved in China has been hard to accomplish elsewhere, mostly because of the freedoms we correctly value in liberal democracies. Worse, there may be a mountain range. In other words, what is happening right now could be just one peak – not the peak. And the reason for this is that despite all those positive signs from antibody testing, the huge majority of the population is not immune. An editorial in the British Medical Journal has reported data from China suggesting that as many as four in five cases of Sars-CoV-2 infection could be asymptomatic. It then goes on to quote people from the Centre for Evidence-Based Medicine in Oxford, who say that if this is true “What the hell are we locking down for?” I wish those people would be brave enough to go and repeat that opinion in an ER in the Bronx right now, in which actual medicine is going on. Worrying about the exact rate of asymptomatic infection, or the currently unknown duration of immunity and a possible “second wave”, is like politely applauding the performance in a jazz club and murmuring “nice” while the building is demolished around you and the piano player gets decapitated. There have been more than 93,000 cases of Covid-19 identified in the UK. Let’s round that up and say it is 100,000. So if the reports from the BMJ editorial are accurate, the actual number would be that multiplied by five, in which case there would have already been half a million infections in the UK. If this really is the peak and we see as many cases on the way down as on the way up, that would total 1 million infections from the initial surge in the UK – hopefully all of those people would then be immune. That would leave about 65 million people in the UK still without immunity. I am going to be unusually optimistic here, and assume that everyone who has Covid-19 becomes fully immune (not a given), and that the virus is towards the less transmissible end of the range of estimates currently available. If this is the case, you would need half your population to have been infected to achieve a level of population immunity that would stop the epidemic continuing to grow and overwhelming healthcare systems. As I write the UK is reporting more than 10,000 deaths from Covid-19. Due to the realities of collecting data during an infectious disease emergency like this, that is likely to be an underestimate. Again, if we assume this is the peak and there is the same number on the way down that’s 20,000 total from the initial surge. And to get to population immunity you have to multiply that by at least 30: based on the current data, that’s about 600,000 deaths to get there, minimum. Finding a vaccine to offer a complete solution to this pandemic is, even in the best scenarios, is still a long way off But it is not hard to see many ways we can slow the pace of the pandemic and save lives. One of them is greatly improved testing to identify cases and their contacts, which could be supplemented by clever digital methods to spot who has been at risk. Governments around the world are attempting ways to keep jobs and businesses afloat while lockdowns are in place – but the pressure remains to swiftly end such shutdowns. I get that this is going to be a mammoth strain on the economy. But the deaths of many thousands of people would be too: it is simply not possible to thoroughly insulate an economy from the impact of a pandemic of this kind. Where I live, in Cambridge Massachusetts, I keep hearing sirens. This crisis is not close to over, quite the reverse. The pandemic is only just getting started. • Dr William Hanage is a professor of the evolution and epidemiology of infectious disease at Harvard