Since its onset in China in December, Covid-19 respiratory infection has resulted in more than 3,100 deaths in more than 92,000 people infected in at least 76 countries and territories.
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If the number of new infections seems to be declining in China, it leaps elsewhere in the world, reaching Tuesday March 3 at 9 am 172 deaths out of more than 10,763 cases, including 4 deaths for 212 confirmed cases in France. While France and many other countries have taken steps to prevent an even wider spread of the coronavirus, take stock of what is known about its contagiousness.
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Is Covid-19 highly contagious?
Are some people more contagious than others?
“A small number of cases could be the spark causing a larger fire,” warned WHO No. 1 Tedros Adhanom Ghebreyesus in early February. He was referring to the case of a Briton infected in Singapore, who then transmitted the virus to a dozen people in total, in France and then in Great Britain. Another example: a 61-year-old follower of the Shincheonji Church of Jesus (a religious organization often accused of being a sect) has become one of the main vectors of coronavirus in South Korea, the second most affected country after China. She alone may have infected several dozen people before being diagnosed.
Some patients who contaminate dozens of people alone are generally called “super-spreaders” or super-contaminators. It’s a phenomenon that has always existed, “explains Sandrine Belouzard. For example, during the Mers coronavirus epidemic that started in 2012, 75% of confirmed cases in South Korea could be linked to only three people. The researchers In particular, they retrospectively demonstrated that a single patient, “patient 14”, alone infected 82 people in just three days.
Why are some more contagious than others?
Problem, it is impossible to recognize a super-spreader. You don’t find them until afterwards, going up the chain. It is therefore unclear why they contaminate far more people than others. “They may be people who secrete more viruses, assumes Sandrine Belouzard. Or who do not necessarily secrete more, but longer.” It is also unclear whether a super-spreader will be for a single virus or for several.
“We know that it exists because the phenomenon has been observed during epidemiological research. But we cannot explain it. Super-spreaders are all the more difficult to spot since the degree of the disease is not necessarily linked to viral load. So you can be a super-spreader without being very sick “
This was particularly the case of Mary Mallon, nicknamed “Mary Typhoid”. Identified as a healthy carrier of typhoid fever, it infected 51 people in the early 1900s without ever developing the slightest symptom itself.
Are some people more vulnerable than others?
While the elderly and sick are the most vulnerable to the Covid-19 epidemic, the absence of casualties among the youngest leaves experts perplexed. “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”, points out Cécile Viboud, epidemiologist at the National Institutes of Health.
So why this apparent immunity in the case of Covid-19? “There are several explanations,” said on Franceinfo the doctor Damien Mascret.
“We think, for example, that children have a much better immune system than adults or the elderly. In other words, if they come across the virus, they become infected, but get rid of it faster. Another hypothesis: some experts believe that children’s lungs are not yet mature enough for the virus to cling properly. Finally, many children are likely to be infected but will not have symptoms. So be careful, they can when even transmit the Covid-19 “
Can we be contaminated twice (or more)?
Japanese authorities announced on February 27 that a young woman who was among the first affected and was declared cured earlier this month was again diagnosed with Covid-19. Second positive diagnoses have also been reported in China. The whole question is whether these people were infected a second time or whether they were still (mildly) infected with the virus when they returned home.
Some experts believe that it is impossible for these people to have been re-infected in such a short time because infected people develop antibodies that provide immunity for a period of time after recovery. Unless the antibodies developed in the case of Covid-19 are insufficient and the immunity is greatly reduced? But the amount of virus detected was generally quite small and these people did not infect anyone else. According to a study published in the Journal of the American Medical Association (JAMA), it is therefore possible that the problem comes from the test: either the quantity of virus was very small and the test returned a “false negative”, or the test has been poorly done.
The fact remains that these cases of “reinfection”, if there is reinfection, bring up the scenario of a new seasonal disease which would be added to the flu and the four human coronaviruses which are already circulating in France and causing colds. mild. In this case, according to The Atlantic, “the cold and flu season would become the cold, flu and Covid-19 season.” But “this remains to be proven,” says Sandrine Belouzard, who calls not to draw hasty conclusions.
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