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MIT Technology Review

Hong Kong researchers say they’ve found the world’s first case of covid-19 reinfection

The discovery could mean the coronavirus is never going away.

Hong Kong airportHong Kong airportWikimedia Commons

The 33-year-old-man arrived by plane in Hong Kong on August 15. After disembarking, he headed to one of the airport’s covid-19 testing stations. Someone swabbed his throat, and then he waited for the results.

The man had come down with the coronavirus in March, suffered fever and headaches, and spent two weeks in a hospital. So he probably didn’t expect to test positive again just 142 days later.

But he did. Was it the original infection lingering in his body or had he caught the virus again, something no one had ever shown was possible?

Scientists at Hong Kong University say they have the answer. On the basis of a genomic analysis of the virus, they say the man got covid-19 a second time, and are calling his case “the first instance of human reinfection” with the novel coronavirus.

The discovery that immunity wears off, if confirmed, could change the math on the pandemic in profound ways. It would mean that surviving the virus is no guarantee of lifelong immunity, that people might have to get vaccinated every year, and that even survivors will still need to wear masks and follow rules on social distancing.

Most of all, it could mean the coronavirus might strike again and again, never really going away.

“Our findings suggest that SARS-CoV-2 may persist in the global human population as is the case for other common-cold-associated human coronaviruses,” Kwok-Yung Yuen, Kelvin Kai-Wang To, and Ivan Fan-Ngai Hung, all professors at Hong Kong University’s medical school, said in a signed statement obtained by the South China Morning Post.

Previously, some people in Japan and elsewhere had tested positive twice for the virus weeks apart, but doctors had concluded that those results were due to test errors or lingering infection.

Researchers in Hong Kong, however, believe that their gene analysis proves this man caught the virus a second time.

Because the virus has gradually mutated as it spreads around the globe, different strains have unique genetic fingerprints. When the Hong Kong researchers compared the genetic sequences of the virus that sickened him in March and the one he had in August, they found differences at 24 positions.

“The team showed that the genome sequence of the virus strain in the first episode of COVID-19 infection is clearly different from the genome sequence of the virus strain found during the second episode of infection,” according to the Hong Kong University statement.

It’s known that four common coronaviruses, which cause colds, frequently reinfect people, sometimes within months. That, along with data showing that antibodies to the new virus fade with time, had previously led some scientists to predict that immunity to SARS-CoV-2 would follow a similar pattern.

If true, it is unlikely that herd immunity can eliminate the virus entirely, according to a copy of the case report posted by Chinese media, since people will constantly be losing their immunity, perhaps after a few months.

That doesn’t mean the virus will remain the danger it is today. People who’ve been infected, or vaccinated, might have fewer symptoms the second or third time around. Some coronavirus experts have suggested that on reinfection the covid-19 germ will stay in the upper airway, causing sniffles, rather than penetrating the lungs to cause pneumonia.

At least in the case of the Hong Kong man, his second infection wasn’t nearly as bad as his first. Doctors say he didn’t show any symptoms of being sick at all.