What are the risks of England unlocking in the Covid third wave?

Lifting the final Covid restrictions in England on 19 July is a gamble for the government. Even without further easing, cases are on course to surpass 50,000 a day by mid-July. Thereafter they could swiftly exceed the winter peak of 81,000 and hit 100,000 or more, the health secretary has said. What the next wave means for lives and the NHS is still deeply uncertain – but the science offers some clues.

Cases

A third wave of coronavirus infections is well under way in the UK. The number of new cases is doubling roughly every nine days, according to the government’s chief scientific adviser, Sir Patrick Vallance. If the pace doesn’t slow, the national epidemic could soon grow larger than the second wave that hit the country in the winter.

Early July has seen average daily cases above 25,000. While Boris Johnson noted at the Downing Street briefing on Monday that cases could reach 50,000 a day by 19 July – the date England is expected to lift the last remaining Covid restrictions – the number could be higher. Even without further easing, which will increase the growth rate, cases could reach 50,000 a day in the week before full reopening and 100,000 a day by the end of the month – more cases than the UK has recorded at any point in the crisis.

Modelling by teams feeding into the government’s Scientific Advisory Group for Emergencies (Sage) anticipates cases rising through July and peaking in August. The majority of infections will be in younger people who are not fully vaccinated. But what happens in the real world is far from clear because of important uncertainties, not least in vaccination rates, coverage, and people’s behaviour relating to mixing and taking precautions after 19 July. Lifting restrictions will undoubtedly give the epidemic a boost, though the closure of schools for the summer holidays will reduce the impact a little.

Hospitalisations and the impact on the NHS

Hospitalisations are expected to track infections with a delay of a week or two. The steep rise in infections will lead to an exponential increase in hospitalisations – meaning they too will double over a fixed period of time – but the rise should be far smaller than seen this winter. The main difference is vaccination, though immunity after natural infection plays a role too. About two-thirds of the UK population has now received one shot of Covid vaccine, with 51% having had both. Because the rollout started with older and more vulnerable people, those being treated in hospital today are younger than they were in the winter and less likely to die from the disease.

Prof Neil Ferguson, who runs the Imperial College modelling group advising Sage, says the ratio of cases to hospitalisations has been cut by more than two-thirds compared with the winter wave, and as more people get their second doses, that reduction will continue. Modelling by the University of Warwick, which necessarily made assumptions about the spread of the virus, vaccine rollout and effectiveness, suggests hospitalisations in England may peak at about 1,300 a day in late July and August, but as ever, the assumptions in the modelling mean little is certain.

This is the gamble the government is taking. At the height of the winter wave, daily hospitalisations peaked at more than 4,000 a day in England, and the NHS may be spared similar pressure this summer. But if cases get very high, in the order of 150,000 or 200,000 a day, then hospitalisations could still put stress on the NHS and deaths will be correspondingly higher.

“Even if vaccines do keep deaths at low levels, current trends in hospital admissions, if extrapolated to the levels of transmission that we know from other countries that this virus can reach, could put a severe strain on the NHS,” said Azra Ghani, professor of infectious disease epidemiology at Imperial.

The focus on coronavirus admissions does not take into account of the demand the NHS will face from patients with long Covid, also known as post-Covid syndrome. Young people and those who are not sick enough to go to hospital with the disease are still at risk of long Covid and may drive up demand on specialist services and long Covid clinics for many months. The NHS is also dealing with an unprecedented backlog of 5 million people awaiting treatment in England.

Deaths

Full vaccination, with two shots of either AstraZeneca or Pfizer, is more than 90% effective at preventing deaths from the Delta variant of Covid. According to Ferguson, deaths from a given number of cases are now 10 times lower than during the winter wave, which peaked in the UK with more than 68,000 cases a day and 1,800 daily deaths. About 99% of UK deaths from Covid have been in those aged 40 and over, and by 19 July nearly everyone in that age group will have been offered two shots of a vaccine.

As the vaccine programme pushes into those aged 18 and over, the impact is more on blocking transmission of the virus than on preventing the deaths of the individuals vaccinated. Because younger people have more contacts, they tend to spread the virus more than older groups, but the more cases there are among young adults and schoolchildren, the greater the chance of the virus finding vulnerable people who have not been jabbed, or who had a poor immune response to the vaccine.

Vaccines and herd immunity

All adults should have been offered both jabs by mid-September, but as the vaccination programme rolls on, infections will continue to spread and bolster the population’s immunity further. The rising levels of immunity will slow the spread of the virus, but to make the epidemic fizzle out, the country must reach the elusive threshold for herd immunity.

The threshold itself isn’t clear-cut, and varies depending on who spreads the virus, but if the R (reproduction) number for an unmitigated Delta variant epidemic is seven, as Public Health England’s Dr Susan Hopkins told MPs, then transmission may need to be completely blocked in at least 85% of the population.

The Office for National Statistics estimates that more than 85% of adults in England have antibodies to coronavirus, but having antibodies does not necessarily stop people becoming infected and passing the virus on. And since adults make up only 80% of the population, there is still some way to go. The threshold may only be met when everyone has good immunity from multiple vaccine doses or infections.

New variants

More infected individuals means a higher risk of new variants emerging. The UK’s planned easing of restrictions, coupled with its strategy of vaccinating down the age groups, makes a substantial epidemic likely in the coming weeks, and with that comes a real risk of new variants. The Delta variant is more dangerous largely because it is so transmissible, though it is also a little more resistant to vaccines. The risk in the months ahead is that a new variant emerges that has substantial vaccine resistance. If that happens, an autumn booster programme, which is being planned for the 50s and over, may be enough to keep the epidemic under control. But in the longer term, vaccines are expected to need updating to match the most common variants in circulation.

“With just over 50% of the population fully vaccinated, by letting the virus run through the population, we are creating the perfect conditions for the selection of mutations that allow the virus to evade the vaccine. This strategy may therefore not only be risky for England, but could also set back the global fight against the pandemic,” said Ghani.

Reinstating restrictions

Unless a new, more problematic variant pops up, the risk of the next wave overwhelming the NHS remains an unlikely worst-case scenario for outbreak modellers on Sage. It is still absolutely possible, though: previous worst-case scenarios during the pandemic have turned out to beoptimistic. But after previously stressing the need for the lifting of restrictions to be irreversible, Boris Johnson refused on Monday to rule out reinstating restrictions if need be. “If, heaven forbid, some really awful new bugs should appear, then clearly we will have to take whatever steps we need to do to protect the public,” he said.