In the UK, the number of confirmed coronavirus cases keeps on steadily ticking upwards. As of March 12 it had 590 confirmed infections – a 134 case increase on the previous day. Up until now the government’s strategy has been simple: first try and contain the outbreak and then delay the spread, evening out the pressure on the NHS.
But now people involved in the government’s coronavirus response appear to be mooting a new strategy: herd immunity. On March 11, David Halpern – chief executive of the government-owned Behavioural Insights Team and a member of the the Scientific Advisory Group for Emergencies – spoke to BBC News outlining an approach that depended on shielding vulnerable people until enough of the UK population had been infected with Covid-19 that acquired immunity stopped its spread altogether.
On the ITV website, Robert Peston referred to the same idea, writing that the strategy of the British government “is to allow the virus to pass through the entire population so that we acquire herd immunity”. So how does the concept work? People can gain immunity to diseases after being exposed to them, and once enough people are immune to a disease – either through exposure or vaccines – it will stop circulating within a population. That’s herd immunity.
This policy would put the UK government in distinct contrast from China and South Korea who responded to their own outbreaks by several restricting travel and monitoring movements – managing to limit the extent of their current outbreaks. Italy too is trying similar policies – including banning most public gatherings – although it’s still too early to know whether that has stopped the spread of the disease there. We contacted the Department of Health and Social Care to clarify whether herd immunity was part of the government’s official coronavirus strategy, but it did not respond in time for publication.
But how would herd immunity work in the UK if it is adopted? Roughly-speaking – given what we know about the current infection rate of Covid-19 – the disease would need to infect approximately half of the UK population until we achieved herd immunity. Although over 80 per cent of Covid-19 infections are mild – that’d add up to more than six million people at risk of severe symptoms. And according to a Chinese study of 44,415 confirmed cases, around five per cent of people experience critical illness: including respiratory failure, septic shock or organ failure.
The problem is that embracing herd immunity could well put the NHS under immense strain – depending on how well we were able to shield vulnerable people from the disease. Jeremy Rossman, a virologist at the University of Kent, isn’t convinced that accepting herd immunity is inevitable. “I think it’s very likely that with continued containment and delay strategies we will be able to stop the virus spread well before reaching even 50 per cent,” he says. “Even spread over a period of months [widespread infection] is obviously not an acceptable plan. Nor is this a necessary or inevitable outcome, especially with good surveillance, containment, delay and social distancing measures enacted.”
The example of other countries suggests that herd immunity might not be the only ending point of the coronavirus outbreak. In South Korea, which recorded 851 new cases in a single day at its peak, the outbreak is slowing. Yesterday it recorded a total of 242 new cases, after some of the most widespread testing in the world. China – once the centre of the global outbreak – recorded only 31 new cases in the WHO’s latest situation reports. Although it’s difficult to know the precise number of people who have caught the infection in China, it does suggest it’s possible to contain the current outbreak without half of the population catching the disease.
It is possible that China or South Korea will experience subsequent outbreaks – so we still don’t know how effective mass quarantine is in the long run. But while other countries – including Denmark, Spain and the Republic of Ireland – are doubling-down on containment by shutting schools and limiting public gatherings, the UK, or at least some of those close to the government, are leaning in a different direction.
Although the UK government is now moving to the ‘delay’ phase’ of its Covid-19 plan, it’s not clear what role herd immunity will play in this. What we do know is that it is a keen interest of both the Behavioural Insights Team (the so-called “Nudge Unit”) and Boris Johnson’s chief adviser Dominic Cummings – who brought up the topic in a meeting with UK tech leaders on March 11. How influential they prove to be over the coming months may end up determining the result of the UK’s growing coronavirus outbreak.
Matt Reynolds is WIRED’s science editor. He tweets from @mattsreynolds1
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