Covid-19 is becoming less fatal in Europe but we do not know why

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By Adam Vaughan

London becomes busier and busier as lockdown lifts

Keith Mayhew / Images SOPA / Shutterstock

It’s becoming increasingly clear that people are less likely to die if they contract covid-19 now compared to the start of the pandemic, at least in Europe, but the reasons are still shrouded in uncertainty.

A British doctor said the coronavirus was “getting a little less angry”, while an infectious disease consultant at the National University of Singapore claimed that a mutated version of the coronavirus, D614G, made the disease less deadly.

In England, the proportion of people infected with the coronavirus who subsequently died was certainly lower in early August than it was at the end of June. Over the period, that infection mortality rate (IFR) fell from 55 to 80 percent, depending on the dataset used, found Jason Oke of the University of Oxford and his colleagues.

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“It doesn’t appear to be the same disease or as deadly as it used to be when we saw so many people die,” he says. For example, the week of August 17 saw 95 people die and just over 7,000 cases across the UK. In the first week of April, 7,164 died and nearly 40,000 tested positive.

Dividing deaths by case gives a crude case fatality rate of around 1 percent in August, down from nearly 18 percent in April. These numbers don’t represent true IFRs at those times, both because deaths are a few weeks behind infections and because testing regimes have changed over time, but they indicate a change of the IFR. Oke and his colleagues used a more sophisticated method to estimate the change in IFR.

The situation is not unique to England and the rest of the UK, says Oke, who has seen the same pattern repeated across Europe.

However, why this is happening is not so clear. According to data for England, a greater proportion of younger people are infected than happened around the first peak of cases in April, with case rates from August 10-16 being highest among 15-44 years.

Covid-19 is known to be less risky the younger you are, so the changing demographics of those infected could be a plausible reason the disease currently appears less fatal. Yet Oke doesn’t think the change in the age distribution alone is enough to explain what’s going on. There are still a lot of older people who test positive, he says.

Several researchers said New scientist that the other main possible explanation is that cases are handled more efficiently in hospitals.

The jury is out on whether a variant of the coronavirus, known as D614G, explains why covid-19 is becoming less deadly. Paul Tambyah of the National University of Singapore told Reuters that the rise of the D614G mutation had coincided with falling death rates in some countries, suggesting it could be “more contagious but less fatal.”

Other research disagrees, concluding that while D614G may be more contagious, there is no evidence that it is less lethal. A study by Erik Volz at Imperial College London, published this month but not yet peer reviewed, looked at the genome of virus samples taken from 19,000 British patients, as well as whether they had died of covid-19.

“We are not seeing a reduction in the risk of death with the D614G variant,” says Volz. He adds that failure to control the age of patients in the modeling may lead to a “mistaken conclusion” that the mutation “has less severe outcomes.”

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