“Herd immunity” used to be such a nice phrase. Until recently, it was most often deployed by champions of universal infant vaccination, who argued – quite correctly – that an infection can no longer spread when a sufficient proportion of the population has been inoculated against it, develops antibodies and no longer transmits the illness.
This is why the so-called “anti-vaxx” movement has been so dangerous: when a smaller proportion of children are vaccinated against (for instance) measles, the disease returns in force. So – hitherto – herd immunity has been regarded as an uncontentious social good.
The Covid-19 epidemic has, however, loaded these two words with a quite different significance. The UK government, in contrast to its counterparts in most other countries, has been explicitly attracted to a distinctive, three-fold approach:
- Sixty per cent of citizens become infected with the virus, the level at which herd immunity is expected to be achieved in the case of coronavirus.
- The pace of infection is managed – partly by encouraging the self-isolation at home of those experiencing early symptoms – so that the NHS can cope with the rate of patient traffic. But the infection does spread: counterintuitively, this is a good thing (or so the argument goes) because, as the vast majority of the infected recover, so does the nation’s collective immunity grow.
- Meanwhile, those who are most at risk from the virus (principally the elderly) are “cocooned”; for example, the isolation measures for the over-70s announced yesterday by Matt Hancock, the health secretary.
Sir Patrick Vallance, the government’s chief scientific adviser, has been quite explicit about this. As he said on Friday’s BBC Today programme:
“What we don’t want is everybody to end up getting it in a short period of time so we swamp and overwhelm NHS services – that’s the flattening of the peak. Our aim is to try and reduce the peak, broaden the peak, not suppress it completely; also, because the vast majority of people get a mild illness, to build up some kind of herd immunity so more people are immune to this disease and we reduce the transmission, at the same time we protect those who are most vulnerable to it. Those are the key things we need to do.”
Here’s what he’s talking about in visual form:
The Government has also resisted pressure to close schools – in contrast to education authorities in 39 nations worldwide that are already keeping pupils at home. It is true that the precise efficacy of school closure in flu epidemics remains unclear and that most studies have drawn mixed conclusions (especially when studying closures during the swine flu outbreak of 2009).
In addition, UK ministers argue that the sudden exclusion of 10 million pupils, particularly those of primary age, would create intolerable and unexpected childcare problems – not least for those parents employed by the NHS and in social care, precisely when they are most needed.
But it is also possible – though scarcely advertised – that keeping schools open is a low-risk way of building herd immunity. As Ian Donald, Emeritus Professor at Liverpool University and an expert in antimicrobial resistance, pointed out in a tweet on Friday:
“Kids generally won’t get very ill, so the govt can use them as a tool to infect others when you want to increase infection. When you need to slow infection, that tap can be turned off – at that point they close the schools. Politically risky for them to say this.”
Donald’s final, laconic sentence was a bullseye. In the past few days, ministers have grown increasingly nervous of the public emphasis upon “herd immunity” and its Darwinian undertones (exploit the sturdiness of the young, let the disease spread, protect the elderly as much as possible, hope for the best).
On Sunday, Hancock distanced the government from the very objective that its chief scientific adviser had embraced only two days before – declaring herd immunity to be “a scientific concept, not a goal or a strategy”.
This, it might be said, is like Robert Oppenheimer declaring nuclear fission to be a “concept” rather than a “strategy”: it still generated a mushroom cloud. What is certain is that ministers, faced with the human reality of a rising infection rate, are newly jittery about any suggestion that they are not simply resigned to mass contamination but actively seeking it.
Finally, and most strikingly, it is not even clear that the herd immunity principle applies in the case of Covid-19. As one very senior medical source told us on condition of anonymity, “We have been told not to speak to the press. But the truth is that nobody yet knows for sure whether the recovered patient will carry on transmitting the illness or even be safe from re-infection.”
This uncertainty is also reflected in the (limited) studies to date. As Kim Roberts, a virology lecturer at Trinity College Dublin, tweeted on Friday:
“The main problem with the UK strategy is that not enough is known about herd immunity & coronaviruses. These viruses do not trigger robust adaptive immune responses, which is one reason why we get colds caused by coronaviruses every few years, even without extensive mutation.”
In a way, it has been gratifying to see the UK government so clearly deferring to its principal scientific voices: Vallance and Chris Whitty, the chief medical adviser. While President Trump has variously described the pandemic a) a Democrat party “hoax”, b) in retreat, and c) good for the US motorist, Boris Johnson has emphatically ditched the populist playbook and ensured that he is flanked at press conferences by experts.
The question remains, however: what sort of expertise? Both Whitty and Vallance are devotees of behavioural science. At Thursday’s press conference, the former explicitly alluded to the lessons of this relatively new field of study in his discussion of lockdowns and isolation measures:
“An important part of the science on this is actually the behavioural science – and what that shows is probably common sense to everybody in this audience. Which is that people start off with the best of intentions but that enthusiasm at a certain point starts to flag… You start [tough measures] too early and people’s enthusiasm runs out just about the peak [of infection], which is exactly the time that we want people to be doing these interventions.”
Vallance, meanwhile, is so immersed in behavioural science that many in Whitehall have forgotten he was originally a vascular biologist by training (see him here speaking at the Behavioural Exchange Conference in 2019, and note the enthusiasm for behavioural science in the evidence he gave to the House of Lords Select Committee on Science and Technology in June 2018).
“Nudge” science can sometimes be a useful tool in generating health policy. The Behavioural Insights Team has helped to generate prompts that reduce missed medical appointments, as well as strategies for preventive medicine, including the use of Fitbit-style technologies.
In their defence, Whitty insists that he and Vallance are mostly relying on classical epidemiology: the standard science of disease, its transmission and treatment. But this has not ended the debate. In a letter to The Times on Saturday (£), Dr Richard Horton, editor-in-chief of The Lancet, and five other prominent public health experts requested that “the government urgently and openly share the scientific evidence, data and models it is using to inform its decisions on the Covid-19 public health interventions in the UK. This transparency is essential to retain the scientific community, healthcare community, and the public’s understanding, co-operation and trust.”
Underpinning this request is anxiety in the medical profession (not to mention the political class) that huge decisions are being taken on the basis of behavioural-science computer models rather than hard evidence.
Whitty and Vallance have now promised to publish their working, though it remains to be seen whether this will quell the anxiety of those who feel that the UK’s “outlier” response to the epidemic – at odds with the strategy adopted in most other countries – has questionable scientific foundations.
None of the above would even be an issue were it not for the greatest challenge facing the Government: namely, the crisis of capacity in the NHS and social care.
As Chris Cook pointed out in his Budget analysis last week, there is almost no elasticity in the health service and provision for the elderly. Even without a pandemic to deal with, there are few hospital beds to spare.
Small wonder, then, that ministers and officials have been attracted, in this first phase, to relatively small-scale measures (hand-washing, isolation for those with minor symptoms, cancellation of unnecessary journeys).But – as was painfully clear from Hancock’s face on his media rounds this weekend – the serious stuff is about to begin. Cancellation of mass audience events, fast procurement of new critical care equipment, home isolation for the elderly.
“We are moving,” as one senior minister told us, “from ‘nudge’ to ‘thump’.” Will the NHS be up to the task? Who, exactly, will look after the elderly at home? How will they avoid infecting them as they do so?
These, to quote Donald Rumsfeld, are just the known unknowns. The unknown unknowns lie ahead of us on an ill-lit road of uncharted challenge and adversity.
All graphics by Chris Newell