Covid-19: a first proven case of reinfection discovered in Hong Kong

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Once cured from Covid-19, is it possible to become infected with the coronavirus a second time? The doubts that remain regarding immunity and the case of patients recovered from the infection but who tested positive for the Sars-CoV-2 virus are questionable. In Hong Kong, a first proven case of reinfection was discovered.

Can coronavirus infect the same person twice or are you immune after being cured? This is the recurring question, as Chinese and Japanese patients tested positive for Covid-19 several weeks after their recovery and discharge from the hospital. A new discovery is reigniting the debate: in Hong Kong, a first proven case of reinfection with Covid-19 has just been reported. Their study is pending publication in the journal Clinical Infectious Diseases.

Covid-19: a patient tested positive twice, almost 5 months apart

The patient is a 33-year-old man who presented symptoms of the disease and who tested positive for the coronavirus on March 26. After his recovery, he tested negative twice. But on August 15, four and a half months after his first infection, the patient tested positive again at the Hong Kong airport, despite showing no symptoms.

The researchers say that genome sequencing shows that the two strains of the virus are "clearly different." That is why this patient is considered the first proven case of reinfection. But other specialists prefer to interpret this finding with caution: "It is difficult to draw definitive conclusions from a single case. Given the number of infections in the world," said Dr Jeffrey Barrett of the Sanger Center (UK).

Coronavirus: do cured patients still carry the virus?

Before this patient, other cases of possible reinfection had questioned scientists. Next, several hypotheses were raised.

Were patients who recovered and tested positive re-infected or did they still carry the virus? "I am not saying that reinfection cannot and never will, but in a short period of time it is unlikely. Even mild infections should leave at least short-term immunity to virus infection in the recovering patient," explained Florian Krammer, a virologist at the Icahn School of Medicine at Mount Sinai (United States), in New York.

Opinion shared by Dr. Marina Karmochkine, doctor in clinical immunology at the Georges Pompidou hospital in Paris: "The antibodies conferred by this infection will have a protective capacity, undoubtedly for a few months," he explains to BFMTV. However, she specified that this protective capacity is not the same as that obtained with a vaccine and that it is still too early to have a sufficient perspective on the matter.

Covid-19: failed tests?

The explanation for these cases that tested positive several weeks after their recovery could be quite different: Some experts also suggested that the bodies of these patients still contained a small amount of virus that the tests could not detect.

The coronavirus diagnostic test involves removing cells from the back of the nose with a swab. Part of the genetic material of the extracted virus is then amplified using a technique called PCR, which allows it to be better detected.

However, "a negative test does not mean with certainty that there is no more virus in this person," recalled Marc Lipsitch, an epidemiologist at the Harvard TH Chan School of Public Health (United States). The target area of the sample, which may not contain virus at the time of testing, or storage of samples at an inappropriate temperature, which can cause deterioration of the virus.

Sars-CoV-2 virus: hypotheses to be taken with caution

Likewise, the positive tests of patients several weeks after recovery may also have another explanation: a study published last February in the Journal of the American Medical Association (JAMA) indicated that four patients with Covid-19 who fulfilled criteria for discharge hospital and who no longer showed signs of infection had tested positive for the virus between 5 and 13 days later.

These explanations are still only hypotheses, the precautionary principle is valid. To limit the risk of contamination, it is recommended:

Wash hands frequently;

respect social distancing;

coughing or sneezing into the crook of your elbow;

use tissues;

Wear a mask.

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