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The first confirmed case of Covid-19 reinfection in the US has raised doubts about the virus’s “herd immunity” and concerned experts because the patient became more seriously ill after the second infection.
A Nevada man tested positive for Sars-Cov-2, the virus responsible for Covid-19, after developing moderate symptoms in April. He then suffered more severely two and a half months later, requiring emergency oxygen therapy.
Scientists at the University of Nevada who examined the 25-year-old during the period found far more differences in the two genetic fingerprints than could be explained by mutations during a prolonged illness, confirming two separate infections.
“Most of us have thought that re-infection with Covid-19 would likely become common as people’s immunity levels dropped after infection,” said Paul Hunter, professor of medicine at the University of East Anglia.
However, the Nevada case was “very worrying both from the point of view of the very short time between the two infections and the fact that the second illness was more serious than the first,” he added. The study was published in the Lancet Infectious Diseases.
Coronavirus reinfections have been recorded in Hong Kong, Belgium, the Netherlands and Ecuador, but this is only the second time a patient has shown more severe symptoms when the virus returned.
The University of Nevada authors came up with several possible explanations for the severity of the reinfection. The patient may have encountered a very high dose of the virus on the second occasion, causing a more acute reaction. Or it could have come into contact with a more virulent viral strain, although scientists have yet to observe mutations in Sars-Cov-2 associated with more serious disease.
Another explanation would be an unusual phenomenon known as antibody dependent enhancement (ADE). In this counterintuitive and potentially dangerous condition, the presence of antibodies, which are supposed to fight the disease, actually make a subsequent infection worse. ADE has previously been observed in the closely related coronavirus disease Sars in 2003 and in viral diseases such as dengue, but not so far in Covid-19.
“We need more research to understand how long immunity can last for people exposed to Sars-Cov-2 and why some of these second infections, although rare, present as more serious,” said Mark Pandori, lead author of the study. Nevada. “So far we’ve only seen a handful of reinfection cases, but that doesn’t mean there aren’t more, especially since many Covid-19 cases are asymptomatic. At this time, we can only speculate on the cause of the reinfection. “
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The implications of the growing list of Covid-19 confirmed reinfections for vaccine development are far from clear, scientists say.
“As more cases of reinfection emerge, the scientific community will have the opportunity to better understand the correlates of protection and the frequency with which natural infections with Sars-Cov-2 induce that level of immunity,” said Akiko Iwasaki, professor of immunobiology at Yale University. . “This information is key to understanding which vaccines are capable of crossing that threshold to confer individual and herd immunity.”
He added: “Cases of reinfection tell us that we cannot rely on immunity acquired by natural infection to confer herd immunity. This strategy is not only lethal for many, it is also not effective. Herd immunity requires safe and effective vaccines. “
