The daily number of deaths from the new coronavirus jumped unprecedented on Thursday with 38 deaths. A total of 170 people died from this viral pneumonia, all in China. The Minister of Health, however, wanted to be reassuring, Tuesday, about the mortality rate of the 2019-nCoV virus: it would be "clearly below 5%".
Or lower mortality than during the SARS epidemic, which killed 774 people in 2002 and 2003, out of the 8096 people infected.
However, it seems too quick to ensure that the new coronavirus is "less deadly than that of the SAR or the Sea" ... quite simply because it is impossible to establish a precise mortality rate. Arnaud Fontanet, director of the Department of Global Health at the Pasteur Institute, who prefers to speak of the case fatality rate, assures him "it is premature, because there are too many unknowns".
The number of unknown infected
And the most important is the number of people infected. Officially, there are close to 7,700 in China, and around 100 in the rest of the world. But these are only confirmed cases. To get an idea of the real number of people infected, two questions remain unanswered.
First, the reproduction rate of the virus, that is to say the number of people infected by a single infected person. And scientists are also trying to find out at what point the virus is contagious: if it is before symptoms appear, as Chinese authorities said on Sunday, the number of people infected could be much higher. higher than the official figure.
"We are doing serology surveys to find out if infected people have been able to develop antibodies to fight the virus," says Arnaud Fontanet. Clearly, the goal is to find out if some people have contracted the disease without expressing symptoms, or a mild form of the virus, which did not require a medical visit.
"As long as we do not know the number of asymptomatic people or those who have contracted mild forms, we will not be able to know the real lethality rate of the virus," concludes the researcher at the Pasteur Institute.
A virus kills in three or four weeks
What could be established today is the lethality rate of the virus among people hospitalized, since this number is certain. But here again, the result would not necessarily be representative of the dangerousness of the disease. An infected person who is at risk of complications (people over 60 or already sick) usually dies three to four weeks after contracting the virus.
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However, the epidemic began to gain momentum about ten days ago. The number of deaths we know today is therefore rather to be compared to the number of people hospitalized three or four weeks ago, that is to say at the very beginning of the epidemic.
In reality, the exact case fatality rate will therefore not be known until the end of the epidemic. And it is not so serious, says Arnaud Fontanet, who refuses to make an estimate: "What interests us is not only to know how many people will die, compared to those affected, but to avoid a too many deaths in absolute terms ”. There is only one way to do this: to characterize the disease as well as possible, and how it spreads to limit the epidemic.