The Intensive Care National Audit and Research Centre receives notifications from adult critical care units across the UK (excepting Scotland) of all Covid-19 admissions. For the past month, ICNARC has issued weekly reports, which have become increasingly comprehensive and revealing, indicating in detail the characteristics shared by the most seriously ill patients. The data compare outcomes for Covid patients against those for patients admitted to ICUs with viral pneumonia between 2017 and 2019. The information allows us to identify the most vulnerable so that they can be protected, even as people return to work and children return to school.

The most striking figure in the ICNARC report dated 1 May is that 72% of Covid-19 patients admitted to critical care are men. This number has been consistent and compares to 55% of patients requiring an ICU bed for viral pneumonia between 2017 and 2019. The second very clear fact, which is again very widely known, is that vulnerability increases steadily with age. While only 21% of those under 40 who are admitted to an ICU die, the death rate for those over 70 rises to 67%. Third, and less clearly, there appears to be a somewhat higher risk of death among Black (53%) and Asian (54%) patients admitted to an ICU, compared to white patients (46%). These outcomes do not correlate with those recorded for patients with viral pneumonia (2017-19), for whom death rates were far lower, but relatively higher for white (22%) than black (13%) and Asian (20%) patients. Further research on this is needed, but for now it is worth identifying BAME patients as potentially more vulnerable to serious infection.

The ICNARC report also shows a significant rise in the mortality rate of those with a Body Mass Index above 30. Put crudely, being obese is a strong indicator to doctors that serious interventions will be necessary. This is sustained by a recent report, based on data from New York City hospitals, which suggests that Covid-19 patients with a BMI over 30 were three times as likely to be require hospitalisation as they were to be discharged to recover at home. It is not likely, of course, that obesity itself is the problem, but many obese patients have related conditions (comorbidities), notably hypertension and diabetes, and other cardiovascular diseases that are commonly associated with obesity. These all make Covid-19 a far more serious infection.

The ICNARC report sets out very clearly that 66% of Covid patients admitted to critical care required mechanical ventilation within 24 hours, and of those (given that not all outcomes are yet known) 62% later died. This is high, but is down from 66% on 17 April, suggesting that critical care over longer periods is saving lives. Of those who, like Boris Johnson, receive only basic respiratory support (an oxygen mask or CPAP) 83% of patients have been discharged, most like him after about three days.

UK outcomes are now somewhat better than those recorded in New York, where 445 of 650 patients admitted to ICUs were put on ventilators. At 69%, this is higher than in the UK (66%). 64% of those had died at the time the report was published, again higher than the UK average (62%). UK data is now also rather better than from Italy, according to a recent retrospective study of 1591 Covid-19 patients in Lombardy.

The numbers presented in the ICNARC report will continue to change over time as more cases are closed and, we all hope, fewer are admitted to ICUs. We can expect that a greater number will be discharged than will survive, and we all hope that the ratio between the two outcomes will change for the better as more and more effective pharmaceutical interventions are identified. Early reports from clinical trials have suggested the drug Remdesivir, developed for Ebola, has lowered the time spent on mechanical ventilation for those who survived, although as yet there is no evidence that it has saved any lives. The hope is that additional therapeutics will work with or better than Remdesivir. For now, however, we must assume that a mortality rate of between 60% and 70% for those placed on mechanical ventilation will be a feature of the first wave of Covid-19.

It is abundantly clear that school-age children are the least vulnerable, and increasingly clear that they are not great spreaders of the virus to each other or to adults.

Clearly, with such a high death rate for the sickest patients, the most vulnerable must be protected. However, the overwhelming majority of people infected by the virus are not vulnerable to serious infection.

It is abundantly clear that school-age children are the least vulnerable, and increasingly clear that they are not great spreaders of the virus to each other or to adults. Even those advocating a continued lockdown have calculated that a full return to school would increase the now notorious “R” by only about 0.2 (far less than decreasing handwashing or basic social distancing measures). It is also possible, but not yet clear (despite the certainty displayed by Swiss public health officials) that children may lack the receptors properly to contract the virus.

Assuming children do transmit the virus, the principal argument for keeping children out of school is the desire to protect teachers and their families. However, according to the most recent reliable data, a comprehensive survey of teachers in UK state schools conducted in November 2018, teachers as a cohort are among the least vulnerable.

Teachers are predominantly young, white, and female. 74% of teachers are women, 24% of teachers are under the age of 30, and only 2% over 60. Only 13% of teachers are BAME. Some individuals, of course, will have underlying conditions that make them more vulnerable. They can inform their heads about these and be offered support.

The first stage to returning to normality should (but certainly won’t) include opening all schools immediately. We must admit that social distancing is still desirable for adults but not vital or possible for school children. There should not be a staggered restart, with parts of each year group turning up on certain days. That would require parents staggering their return to work or, in many more cases, asking vulnerable grandparents to step in. There should not be a rolling return, allowing some year groups to return earlier than others.

Finally, there is certainly no reason to prioritise the return of year 10 and year 12 students, whose exams have already been cancelled, who are most able to benefit from online learning, and who can safely and legally be left home alone.