Paris (AFP)
Elderly people or those already suffering from another disease such as diabetes, asthma or hypertension are the most vulnerable to the epidemic of new coronavirus, which moreover kills more men than women.
Since its onset in China in December, Covid-19 respiratory infection has resulted in more than 2,800 deaths out of 83,000 people infected in at least 53 countries.
In most cases, it causes mild or moderate symptoms (cough, fever, fatigue ...), but in the most severe cases, patients can enter into severe acute respiratory distress or be victims of acute renal failure , or even a failure of several organs, which can lead to death.
Its average mortality rate remains relatively low - it is not yet known with precision, but it is estimated between 1% and a little more than 3%.
It is much more than the seasonal flu (around 0.1%), but less than the previous epidemics linked to a coronavirus, much more virulent: 34.5% for the Seas (Middle East respiratory syndrome) and 9 , 6% for SARS (severe acute respiratory syndrome), whose virus is close to 80% of the new coronavirus.
The most complete analysis to date, published on February 17 by the Chinese authorities and then on February 24 in the American medical journal Jama, shows that the mortality rate increases markedly with age.
Out of nearly 45,000 confirmed cases, the average mortality rate is 2.3%. But there are no deaths among children under the age of 10. Up to the age of 39, the mortality rate remains very low, at 0.2%, then drops to 0.4% in those in their forties, 1.3% in those aged 50-59, 3.6% in those aged 60- 69 years and 8% in the 70-79 age group.
People over the age of 80 are most at risk with a death rate of 14.8%.
Outside of China, there are also many elderly people among the victims. In Italy, the most affected country in Europe, at least six people among the first 14 deaths were aged 80 or over.
- No young children -
The absence of victims among the youngest leaves experts perplexed, since infants and young children are usually among those vulnerable to infectious diseases.
"This is surprising, because when we look at all the other respiratory infections - bacterial or viral - we almost always have a lot of serious cases in the very elderly, but also in the very young, especially those under the age of five", underlines Cécile Viboud, epidemiologist at the National Institutes of Health (United States).
"We have to look if there is not a form of cross protection due to the recent epidemic of seasonal coronaviruses", those which cause a simple cold, observes John M. Nicholls, professor of pathology at the University of Hong Kong. A second hypothesis is that the immune system of children is designed "not to overreact in the presence of new infectious agents".
Another notable characteristic of Covid-19, men are more threatened than women by a fatal outcome: while they represent 51.4% of the cases confirmed in this study, they account for almost two-thirds of deaths (63, 8%).
- Tobacco aggravating factor -
This could be explained "at least in part" by the higher proportion of smokers among men, points Cécile Viboud, tobacco being among the parameters that increase the risk of death.
Differences in behavior or immune response are also advanced as hypotheses.
Chinese statistics also give indications of other possible risk factors, including having a chronic disease.
The mortality rate climbs to 6.3% in patients with respiratory disease (respiratory failure, asthma, chronic obstructive pulmonary disease ...)
It is even 10.5% in those who have a cardiovascular disease (heart failure, history of stroke or infarction ...) and 7.3% in people with diabetes.
Patients with hypertension (6%) or cancer (5.6%) also have a higher mortality rate, while it drops to 0.9% in healthy people.
These profiles are found among victims from other countries. Thus, in Italy, among the first 14 victims, one was hospitalized for cancer, another had a heart attack a few days earlier, a third suffered from heart conditions and was on dialysis, and at least two others had serious diseases.
If the overall mortality of infected Chinese health professionals remains low, in the published figures (0.3%), the young age of several of them strikes, because it comes out of the typical profile of other victims.
David N. Fisman, an epidemiologist at the University of Toronto, says that young caregivers are more likely to be in direct contact with the sick than older people. John M. Nicholls also puts forward a probable "lack of experience and training" in "taking care of contagious patients" and in using protective equipment correctly, when they are overwhelmed by the influx of patients and the previous comparable situation, the SARS epidemic, dates back 17 years.
As with other infectious diseases such as the flu, people who do not have risk factors should not feel exempt from the recommended precautionary measures (frequent hand washing, coughing in their sleeves, etc.).
These "barrier measures" in fact avoid transmitting the virus to more fragile people, who are likely to develop a severe or even critical form of the disease.
© 2020 AFP