Less deadly than SARS, but more transmissible, perhaps even before the onset of symptoms: the robot portrait of the new coronavirus is gradually emerging and the comparison with its close relative, responsible for 800 deaths in 2002/2003, gives clues to fight the epidemic.
"From what we see now, this disease is not (...) as powerful as SARS," said Gao Fu, head of the China Center for Disease Control and Prevention on Sunday.
"We have the impression (...) that today the spread of this virus is faster than SARS, but that on the other hand mortality is much lower", added the French Ministry of Health, Agnes Buzyn. France is one of the countries outside China where a few cases have been detected.
According to the WHO, the SARS epidemic had killed 774 people worldwide out of 8,096 cases in 2002/2003 before being brought under control, ie a mortality rate of 9.5% (compared with 34.5% for the only other epidemic caused by a coronavirus, the Mers).
The new virus has so far killed 81 people, all in China, out of 2,744 reported cases (plus around 40 abroad), ie a mortality rate of less than 3%.
However, this figure is only indicative: we do not know the real number of infected people since patients with few, if any, symptoms were probably not detected.
"Rather, the death rate seems to be going down day by day, because we are discovering more cases," said Buzyn. "So the number of deaths compared to the number of cases means that mortality seems to be reduced compared to what we initially feared."
Scientists at Imperial College London estimate that "on average, each case (of patients with the new coronavirus) has infected 2.6 other people".
Called "basic reproduction rate" (or R0), this measure is important for understanding the dynamics of an epidemic.
In the case of SARS, it is estimated that each case infected on average 2 to 3 other people (like the common seasonal flu), but with great disparities: there were "super-transmitters" capable of infecting dozens of people.
In the case of the new virus, one question is crucial: the stage of infection at which a patient becomes contagious.
"Contagion is possible during the incubation period", that is to say even before symptoms appear, said Ma Xiaowei, head of the Chinese National Health Commission (CNS), on Sunday. "It is very different from SARS," he insisted.
However, this hypothesis is based on the observation of a few initial cases and has not yet been confirmed with certainty.
"If it is something rare, it will have only a minimal impact on the evolution of the epidemic, but if it is frequent, it will be more and more difficult to control it", explains the virologist Jonathan Ball, of the University of Nottingham (England).
In fact, if a patient is contagious even before symptoms appear, the spread of the virus will be more difficult to contain, especially since the incubation period can be up to two weeks, according to estimates.
In this scenario, "measures such as (temperature) control at airports would be ineffective," said British professor Sheila Bird.
The disease caused by the new coronavirus and SARS have common symptoms, according to the observation of the first 41 cases identified in China.
All of these patients had pneumonia, almost all had fever, three-quarters coughed, more than half had difficulty breathing.
But "there are important differences with SARS, such as the absence of symptoms affecting the upper airways (runny nose, sore throat, sneezing)", analyzes Professor Bin Cao, main author of this work published on Friday in The Lancet.
The average age of the 41 patients is 49 years and less than a third suffered from chronic diseases (diabetes, cardiovascular problems ...). Almost a third developed acute respiratory distress and six died.
Although there is no general conclusion to be drawn given the small number of patients considered, these observations provide an initial clinical picture of the disease.
These indications are all the more precious as the diagnosis is made difficult by the flu epidemic which is currently raging, with similar symptoms.
There is no vaccine or medication for the coronavirus, and medical management is about treating the symptoms.
- Control the epidemic
The SARS epidemic had been contained in a few months thanks to a large international mobilization. China had imposed strict hygiene measures on its population (including the wearing of masks), and isolation and quarantine devices had been implemented. Hence the importance of knowing if the new coronavirus can be transmitted even without symptoms.
In addition, China had banned the consumption of civets, a mammal through which the virus was transmitted to humans.
In the case of the new virus, it is not yet known which animal plays this role of intermediary. Until it is known, China has banned the trade in all wildlife.
© 2020 AFP