"More people are getting COVID-19 twice, suggesting immunity wanes quickly in some" - sciencemag.org [View all]

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South Korean scientists reported the first suspected reinfections in April, but it took until 24 August before a case was officially confirmed: a 33-year-old man who was treated at a Hong Kong hospital for a mild case in March and who tested positive again at the Hong Kong airport on 15 August after returning from a trip to Spain. Since then, at least 24 other reinfections have been officially confirmed—but scientists say that is definitely an underestimate.

To count as a case of reinfection, a patient must have had a positive polymerase chain reaction (PCR) test twice with at least one symptom-free month in between. But virologist Chantal Reusken of the Dutch National Institute for Public Health and the Environment (RIVM) explains that a second test can also be positive because the patient has a residue of nonreplicating viral RNA from their original infection in their respiratory tract, because of an infection with two viruses at the same time or because they had suppressed but never fully cleared the virus. So most journals want to see two full virus sequences, from the first and second illnesses, that are sufficiently different, says Paul Moss, a hematologist at the University of Birmingham. “The bar is very high,” Moss says. “In many cases, the genetic material just isn’t there.”

Even if it is, many labs don’t have the time or money to clinch the case. As a result, the number of genetically proven reinfections is orders of magnitude lower than that of suspected reinfections. The Netherlands alone has 50 such cases, Brazil 95, Sweden 150, Mexico 285, and Qatar at least 243.

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They could become more common over the next couple of months if early cases begin to lose their immunity. Reinfections with the four coronaviruses that cause the common cold occur after an average of 12 months, a team led by virologist Lia van der Hoek at Amsterdam University Medical Center recently showed. Van der Hoek thinks COVID-19 may follow that pattern: “I think we’d better prepare for a wave of reinfections over the coming months.” That’s “bad news for those who still believe in herd immunity through natural infections,” she adds, and a worrisome sign for vaccines."

From: https://www.sciencemag.org/news/2020/11/more-people-are-getting-covid-19-twice-suggesting-immunity-wanes-quickly-some

Well, reinfection occurs with the other four coronaviruses which cause the so-called common cold. So, it's not surprising if it happens with the COVID virus also.