Only about half of the sickest Covid-19 patients, admitted to intensive care struggling to breathe, are being put on mechanical ventilators, it has emerged, as evidence grows that many do better with non-invasive help.

The rush to increase the number of ventilators in Britain from 8,000 to 18,000 was a response to early assumptions that intubation was the only way to save the lives of those who become severely ill. Industry was urged to switch production, and Dyson was among the companies volunteering to help, but it has now been told by the government its services are not needed.

This may now look like an over-reaction, but one leading intensive care expert said the government had little choice. The Imperial College modelling prediction of 250,000 UK deaths was based partly on a shortfall in the number of ventilators in the NHS.

“It is easy in retrospect,” said Mervyn Singer, a professor of intensive care medicine at University College London. “Governments had to prepare for the worst and hope for the best. The truth is usually somewhere in the middle.”

Singer talked to colleagues in China and in Italy about their experiences before the UK’s intensive care units started to fill up. “We started off with a strategy to try to avoid intubation,” he said.

The alternatives to mechanical ventilation include continuous positive airway pressure (Cpap). Cpap machines are a type of ventilator that uses a mask but delivers air at mild pressure without taking over the function of the lungs. It is believed Boris Johnson was treated with Cpap.

Quick guide Will there be a second wave of coronavirus? Show Hide In recent days the UK has seen a sudden sharp increase in Covid-19 infection numbers, leading to fears that a second wave of cases is beginning. Epidemics of infectious diseases behave in different ways but the 1918 influenza pandemic that killed more than 50 million people is regarded as a key example of a pandemic that occurred in multiple waves, with the latter more severe than the first. It has been replicated – albeit more mildly – in subsequent flu pandemics. Until now that had been what was expected from Covid-19.

How and why multiple-wave outbreaks occur, and how subsequent waves of infection can be prevented, has become a staple of epidemiological modelling studies and pandemic preparation, which have looked at everything from social behaviour and health policy to vaccination and the buildup of community immunity, also known as herd immunity. Is there evidence of coronavirus coming back in a second wave? This is being watched very carefully. Without a vaccine, and with no widespread immunity to the new disease, one alarm is being sounded by the experience of Singapore, which has seen a sudden resurgence in infections despite being lauded for its early handling of the outbreak. Although Singapore instituted a strong contact tracing system for its general population, the disease re-emerged in cramped dormitory accommodation used by thousands of foreign workers with inadequate hygiene facilities and shared canteens. Singapore’s experience, although very specific, has demonstrated the ability of the disease to come back strongly in places where people are in close proximity and its ability to exploit any weakness in public health regimes set up to counter it. In June 2020, Beijing suffered from a new cluster of coronavirus cases which caused authorities to re-implement restrictions that China had previously been able to lift. In the UK, the city of Leicester was unable to come out of lockdown because of the development of a new spike of coronavirus cases. Clusters also emerged in Melbourne, requiring a re-imposition of lockdown conditions. What are experts worried about? Conventional wisdom among scientists suggests second waves of resistant infections occur after the capacity for treatment and isolation becomes exhausted. In this case the concern is that the social and political consensus supporting lockdowns is being overtaken by public frustration and the urgent need to reopen economies. However Linda Bauld, professor of public health at the University of Edinburgh, says “‘Second wave’ isn’t a term that we would use at the current time, as the virus hasn’t gone away, it’s in our population, it has spread to 188 countries so far, and what we are seeing now is essentially localised spikes or a localised return of a large number of cases.” The overall threat declines when susceptibility of the population to the disease falls below a certain threshold or when widespread vaccination becomes available. In general terms the ratio of susceptible and immune individuals in a population at the end of one wave determines the potential magnitude of a subsequent wave. The worry is that with a vaccine still many months away, and the real rate of infection only being guessed at, populations worldwide remain highly vulnerable to both resurgence and subsequent waves. Peter Beaumont, Emma Graham-Harrison and Martin Belam

Early fears were that healthcare workers would be more likely to be infected by Cpap patients, but at University College hospital that turned out to be unfounded.

Singer and his colleagues wrote an algorithm for deciding which patients needed intubation and which could be given other forms of breathing support. They launched their care pathway on 20 March, the day that London’s Northwick Park hospital had to declare an emergency and send Covid-19 patients to other hospitals. “They were intubating everyone as per guidance and ended up with no ventilators left and had to declare a critical emergency,” said Singer.

Around the world, doctors are increasingly reluctant to use mechanical ventilation for any but the severest cases. A study of outcomes in New York published on Wednesday in the Journal of the American Medical Association found that 88% of those put on mechanical ventilation in critical care units died.

But that’s a Catch 22 situation, say UK experts. These were probably the sickest patients, whose lungs were barely functioning and would have died without invasive ventilation.

Prof Anita Simonds, a consultant in respiratory medicine at Royal Brompton hospital, said the very poor outcome in New York patients was “probably not a fair assessment” because there were still patients in intensive care, so the survival rate may yet go up.

“My view, which I think is fairly widely held, is that some of the comparisons being made are not apples and apples. As is appropriate with evolving information, these plans are iterative in how you manage patients. We’ve learned as we’ve gone along,” she said.

For maybe 30% or even 50% of Covid patients, non-invasive Cpap ventilation with extra oxygen at high levels can be sufficient. “If that is sufficient for them, the outcome in that cohort – survival and other measures like length of time in hospital – will be better than those who had invasive ventilation. That’s largely because they include a less-ill group of patients,” she said.

“The group who go on to be intubated, often they’ve had a trial of Cpap which has failed or they’ve deteriorated so rapidly you have no hope of treating them so they have to be intubated. They are sicker patients and their outcome will be poorer.”

Cpap is not the only non-invasive ventilation method being tried for Covid-19 patients. It is one of three now included in a trial called Recovery RS, sister to the Recovery trial for new drug treatments for the disease. Mechanical ventilation is not included.

Singer said hospitals had to be very careful how they ventilated patients, given the staffing pressures in intensive care units. “I think the general view is that if you can keep a patient off a ventilator, they will do well,” he said. “But it’s catch 22. Sicker patients have sicker lungs.”