While coronavirus infections have been surging again across Europe since late summer, the chances of surviving the respiratory disease seem to have improved from the first phase of the outbreak.
The number of Covid-19 patients ill enough to go to hospital has risen less steeply — and mortality more slowly still, according to an FT analysis. Health services are not overwhelmed as they would have been if severe disease had followed infection in the way it did between March and April.
“In western Europe, pretty much every country including the UK is still seeing a much smaller per capita death rate in this second wave than in the first one during the spring,” said Mark Woolhouse, professor of infectious disease epidemiology at the University of Edinburgh.
The falling “case fatality rate” — deaths as a proportion of confirmed cases — can be explained partly by increased testing, which reveals more infections, and by the fact that a higher percentage of people with Covid-19 today are young and less likely to become severely ill than patients in the spring.
But even patients admitted to critical care are more likely to survive now than their counterparts earlier in the pandemic. Data from ICNARC, the UK Intensive Care National Audit and Research Centre, show that the proportion who died within 28 days of admission fell from 39 per cent in the months to August 31, to 27 per cent after September 1.
The increase in 28-day survival was most notable in patients under 70. It rose from 61 to 79 per cent among those aged 50 to 69, and from 82 to 91 per cent among under-fifties.
Improvements are being seen across a wide range of patients, including those with additional chronic health problems, and those with very low blood oxygen saturation levels, an indicator of particularly severe respiratory illness.
Paul Hunter, professor of medicine at the University of East Anglia, attributed about half of the improvement to the use of dexamethasone and other steroid medicines to reduce inflammation and damp down patients’ overactive immune systems.
“The rest is probably down to the experience of doctors and nurses learning how to treat patients,” he said. “We see this in any epidemic, when medics flail around for a bit as they discover what works best. With Ebola, for example, mortality rates fell during the epidemic in west Africa.”
Peter Openshaw, professor of experimental medicine at Imperial College London, has a similar explanation. “People have learnt many little tricks which, when added together, make a big difference over time.”
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For instance, clinicians are gaining a better sense of when to give patients blood thinners, when to put them on ventilators and when to place them in a prone position on their stomach to increase oxygen intake.
The age composition of Covid-19 hospital patients has also shifted, with over-sixties accounting for less than half of patients in August, down from 70 per cent in February, according to data compiled from 44 countries by ISARIC, the International Severe Acute Respiratory and Emerging Infection Consortium.
But improved hospital outcomes are not just the result of shifting patient demographics: in-hospital mortality among over-sixties halved from 50 per cent in early spring to 25 per cent in August.
Nonetheless, interpreting trends in hospital mortality remains tricky, as there are many differences between the spring and autumn cohorts of patients beyond their age composition.
“It is extremely hard to compare the people who were hospitalised when it was incredibly difficult to even get a test and people were waiting a long time to go in and those today who are tested at the slightest sign of symptoms and get admitted much more easily,” said Gideon Meyerowitz-Katz, an epidemiologist at the University of Wollongong in Australia.
The number of people in hospital with Covid-19 is rising again across much of Europe, with occupancy levels already exceeding half of their spring peak in several countries particularly in eastern Europe. Current patient numbers in the Czech Republic are far higher than in March and April.
In terms of mortality, Europe’s Covid-19 resurgence is proving less frantic than the original spring surge, with death rates climbing more slowly this time. Since deaths began rising again in late summer, it has taken one month on average for them to reach one death per million people. In March the same ascent took one week.
Scientists also discuss more speculative reasons why Covid-19 may be becoming less lethal.
One is that people who become infected today receive lower doses of coronavirus than six months ago, for behavioural reasons including more cautious social interactions and wearing masks. In many respiratory infections, a smaller viral load tends to produce less severe disease though there is no direct evidence for Covid-19.
Another factor that is sometimes mentioned — and dismissed by most viral geneticists — is that the virus has mutated to become less virulent but perhaps more infectious.
“Scientists who have credibility on the genetics of virulence tell me that this has not changed yet,” said Prof Hunter, “but that doesn’t mean that it will not change eventually”.
A plausible theory, he added, was that two other previous coronaviruses could have jumped from animals into humans — “one in Tudor times and the other in Victorian times” — and caused epidemics with many deaths, which were regarded then as outbreaks of severe influenza. Their viral descendants still circulate among people today, causing symptoms no worse than a common cold.
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