Chinese and Japanese authorities have reported that several people recovered from CoVid-19 infection have tested positive for a second time against the new coronavirus called Sars-CoV-2. Researchers are wondering about the immune response to this infection.
- No reinfection, but rather an evolving disease
- Unreliable diagnostic tests?
- Asymptomatic carriers: a low risk of contagion
Can we get sick again when we have already contracted CoVid-19 ? Or is it almost impossible as with chickenpox? This is the question researchers around the world are asking after a Japanese patient and several Chinese patients tested positive for Sars-CoV-2 infection a second time when they were considered cured.
In the case of the Japanese woman, she had tested positive for the new coronavirus last January. She was taken into hospital before she could go home. But a few weeks later, she suffered from sore throat and chest pain again and was therefore readmitted to hospital. Chinese patients, on the other hand, were asymptomatic when they tested positive a second time during follow-up examinations.
No reinfection, but rather an evolving disease
According to some researchers, this is not a reinfection, but rather traces of virus that are not completely gone. Interviewed by the New York Times , Florian Krammer, virologist at the Icahn School of Medicine at Mount Sinai in New York, explains: ” I’m not saying that reinfection is impossible but in this short period of time, it is unlikely Even the mildest forms of infection must leave at least short-term immunity to the virus in the recovering patient . ”
A vision shared by Anne-Marie Moulin, researcher at the SPHERE laboratory of the CNRS, who explains to Doctissimo that ” this does not prove that the antibodies will protect from a second attack but suggests that they play a role in the favorable evolution of the ‘infection ‘.
Other scientists also discuss the possibility of a biphasic infection: a virus that would persist in latent form in the body and which could become more symptomatic when the lungs are affected.
A recent Chinese study published in The Lancet also showed that the average duration of viral excretion, defined as the expulsion of viral particles from the body, was 20 days in survivors of CoVid-19 infection. In the 54 deceased people studied, the virus was detectable from the onset of the disease until their death.
Unreliable diagnostic tests?
Virologist Jin Dong-yan, interviewed by the South China Morning Post , did not rule out the possibility of a diagnostic error. ” It is not a second infection or a persistent infection, as some people might think. It is either because the patients experienced a long course of the disease, or because the diagnostic tests were not done correctly .”
The diagnostic test for the new coronavirus consists of a microbiological sample from the upper and lower respiratory tract (nose and bronchi). This sample is then sent for analysis to a laboratory. In China, patients are considered cured when two other diagnostic tests are performed and the results are negative. However, the samples taken can be stored at a temperature that deteriorates the virus. Or, the sampled area may not be affected by the virus found elsewhere in the body, which again falsifies the test.
” A test is considered positive if the virus is on the swab in sufficient quantity at the time when the sample is taken , specifies indeed the epidemiologist Marc Lipsitch. A negative test does not necessarily mean that the virus is no longer present “. Interviewed by Doctissimo, Olivier Schwartz, director of the Virus and Immunity Unit of the Pasteur Institute, adds: ” The most likely thing is that the viral load had dropped until it was below the detection limit of the test, then went up again afterwards “.
Asymptomatic carriers: a low risk of contagion
If the question of the reliability of diagnostic tests arises, the researchers also want to know whether these patients who test positive for a second time with Sars-CoV-2 but who are asymptomatic have the capacity to infect other people.
An unlikely hypothesis according to the Director General of the World Health Organization (WHO) Tedros Adhanom Ghebreyesus who said on March 3, 2020: ” With influenza, infected but asymptomatic people are important drivers of transmission, which does not does not appear to be the case with CoVid-19. Chinese data shows that only 1% of reported cases are asymptomatic, and most cases develop symptoms within two days of infection . ”