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Can a cured patient with COVID-19 again get a positive result? This key question in the fight against a pandemic remains without a definitive answer, although scientists hope to prove that the immunity to the virus is at least several months.
“Being immunized means having developed an immune response to the virus that eliminates it. And since this answer has a memory, it prevents future infections. ” explains Eric Vivier, professor of immunology at the State Aid Hospital of Marseille (southeast France).
In general, to fight RNA-like viruses, such as SARS-CoV-2, “it takes about three weeks to produce enough antibodies” that protect against the virus for several months, he says.
But here’s the theory: it’s too early to determine if the same thing happens with the new coronavirus.
“We can only extrapolate it to other coronaviruses, and even data on them is limited.” admits Mike Ryan, director of emergency programs at the World Health Organization (WHO).
During the SARS, which killed nearly 800 people in the world in 2002-2003, the treated patients were protected “on average from two to three years,” says AFP Dr. Francois Ballou from University College London.
Thus, “You can get infected again, but the question is, how long? We will know this in hindsight, ”Ballu predicts.
Are antibodies equal to immunity?
A study of 175 patients treated in Shanghai, published in early April without an assessment, showed that most generated neutralizing antibodies 10-15 days after the onset of the disease, with various concentrations.
But detecting the presence of antibodies is not the same as concluding that they give immunity, according to Maria Van Kerchove, who is responsible for fighting the pandemic at WHO.
“We are trying to find out if the one who signed the contract with COVID is really protected (…)”, Dr. Jean-Francois Delfrassy, president of the science council who advises the French government on the pandemic, said Wednesday.
And what could be worse: “We don’t know if antibodies produced against the virus can aggravate the disease.” According to Tanguy, who recalls that the worst symptoms of COVID-19 appear late when the patient has already developed antibodies.
There are also no elements allowing us to find out who produces the most effective antibodies: seriously or moderately sick, elderly or young.
Faced with these unknowns, some experts question the relevance of achieving collective immunity, that is, when the number of infected people is large enough to prevent new infections in the population.
“The only real solution is the vaccine” Archie Clements, epidemiologist at Curtin University of Australia, estimates.
Immune passport?
Despite all this, in countries such as the United Kingdom and Finland, serological tests were performed to detect antibodies to determine the percentage, possibly a very low percentage of the infected population.
In Germany, the research body even proposed a kind of “passport” of immunity so that people who have already produced antibodies can resume their work.
“It’s too premature,” Dr. Saad Omer, director of the Yale Institute for Global Health, assures AFP, offering to wait a few months, “when there will be sufficiently sensitive and specific serological tests.”
Researchers insist, first of all, that these tests should not be erroneous in detecting antibodies to other benign circulating coronaviruses.
Certificates of immunity also raise ethical issues, according to some researchers.
“People who need to go to work to feed their family may want to get it.” Ballu warns.
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