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7 June 2021updated 21 Sep 2021 5:46am

Will a third wave of Covid-19 delay the UK’s unlocking?

If the vaccine rollout has gone so well, why is the Delta variant a problem?

By Harry Lambert

How well protected is the UK from a third Covid wave? On the surface, the UK has, over the past the six months, built a formidable shield against the disease. For every ten British adults, four have been double-dosed with a vaccine, two have been single-dosed, and one (of the remaining four) likely has some degree of protection from Covid thanks to prior infection. Only three are likely to lack any defence from the disease.

As a second wave was building in December, when we first wrote about the life-saving potential of vaccines, eight in ten lacked any protection (two in ten having been infected). We are in a different world today.

And yet the government’s final stage of reopening, tentatively set for a fortnight’s time, may well have to be delayed by a few weeks, given the rise of the new Delta, or Indian, variant. Why?

[see also: How the 21 June reopening date became about more than data]

There are two key reasons. First, there are a significant number of people still unvaccinated who are at risk of ending up in hospital. Second, none of the vaccines on offer appear to be 100 per cent effective, so some portion of those given a jab will be ineffectively vaccinated.

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“You can get quite a long way just by knowing those two numbers,” says James Ward, a risk consultant whose Covid models have attracted widespread interest. Ward’s models show that “about 45,000” might die if an exit wave ran through all those still at-risk across the UK.

How so? Take the first variable: the unvaccinated. Nearly 320,000 people across England aged 65 or over have not been given a first dose of vaccine. If all of them contracted the disease, we would – given infection fatality rates thus far – expect around 16,500 deaths among them, or nearly 20,000 across the UK, as per a New Statesman analysis. There are a further 1.6 million unvaccinated 40- to 64-year-olds across England. If all were to contract Covid, we would expect around 6,000 deaths among them, extrapolating across the UK.

This is one reason why cases cannot advisably be allowed to spiral out of control in the following months: cases and hospitalisations have not been entirely “decoupled”. Despite one of the most comprehensive vaccine roll-outs in the world – with 97 per cent of those 65 and over having had a first dose – there are still hundreds of thousands of unvaccinated people in at-risk groups. There is a risk of 25,000 or so deaths among them if all were infected.

In reality, it is unlikely that everyone still at-risk would be infected in a world without restrictions. Populations reach herd immunity – the point at which the rate of infection or the R number falls and remains below 1 – without 100 per cent protection. And seven in ten people, as we know, now have some of defence from Covid. Nevertheless, the new Delta variant is spreading. We have not reached herd immunity yet. The unvaccinated still pose a risk.

The second key reason why cases must be kept under control is the risk to the ineffectively vaccinated (those for whom the vaccine doesn’t work). This is the other major variable in any Covid projection. Here, Ward’s model – based on the public data available thus far –assumes two doses of the Covid vaccine is 98 per cent effective at protecting against hospitalisation and death. That may prove an overestimate, but even that very high level of effectiveness could lead to around 15,000 deaths in the ineffectively vaccinated – in addition to the 25,000 or so possible fatalities among the at-risk but unvaccinated.

Where does that leave the decision to reopen? The dynamics of Covid are difficult to predict. “If we hadn’t had Delta, all the debate would be around can we bring forward June,” Ward tells me, “Delta’s changed that, we now think there will be some kind of exit wave.”

Forecasting how Covid will play out is like “nailing different bits of jelly to a wall” says Professor Oliver Johnson, director of the Institute for Statistical Science at the University of Bristol. “It gets quite messy quite fast.” Johnson’s analyses have shown that cases are currently rising exponentially ­– they are rising linearly on a log graph – albeit from a low base. After the next stage of reopening, transmission would increase, but by how much? At the same time, more vaccines will provide an ever greater shield, but how much of one?

[see also: Why delaying the 21 June unlocking is such a political headache for Boris Johnson]

The uncertainty has led to renewed calls to delay the 21 June reopening. But, Ward points out, there are also compelling reasons why, even with rising cases – and the need to prevent infection among both the unvaccinated and ineffectively vaccinated – the government may be wise to “exit” Covid this summer and drop all restrictions as planned. If the government instead waits until, say, everyone eligible in the UK has been double-dosed, the problem is “that takes you well into September”. 

Not only would Britain’s summer of renewed freedom be delayed, but any future exit wave may be worse when the weather changes and schools and universities return. “The longer we drag it out, the worse it may get again,” Ward notes, as new and ever more transmissible variants take hold, as they have over the past year.

The ideal outcome – an unlocking that doesn’t lead to an exit wave – may no longer possible under the Delta variant. The government may well reasonably delay the 21 June reopening by a few weeks until July, giving it more time to administer vaccines to adults under 30, who are the most likely to transmit Covid.

But there is no guarantee that a longer delay would buy the UK greater safety from a final wave. A degree of risk will remain, even with the UK’s remarkably high rate of vaccine take-up, and vaccines that appear to be extremely effective at preventing hospitalisations.

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