First documented coronavirus reinfection reported in Hong Kong

By Apoorva Mandavilli
The New York Times Company

A 33-year-old man was infected a second time with the coronavirus more than four months after his first bout, the first documented case of so-called reinfection, researchers in Hong Kong reported Monday.

The finding was not unexpected, especially given the millions of people who have been infected worldwide, experts said. And the man had no symptoms the second time, suggesting that even though the prior exposure did not prevent the reinfection, his immune system kept the virus somewhat in check.

“The second infection was completely asymptomatic — his immune response prevented the disease from getting worse,” said Akiko Iwasaki, an immunologist at Yale University who was not involved with the work but reviewed the report. “It’s kind of a textbook example of how immunity should work.”

People who do not have symptoms may still spread the virus to others, however, underscoring the importance of vaccines, Iwasaki said. In the man’s case, she added, “natural infection created immunity that prevented disease but not reinfection.”

“In order to provide herd immunity, a potent vaccine is needed to induce immunity that prevents both reinfection and disease,” Iwasaki said.

Doctors have reported several cases of presumed reinfection in the United States and elsewhere, but none of those cases have been confirmed with rigorous testing. Recovered people are known to carry viral fragments for weeks, which can lead to positive test results in the absence of live virus.

But the Hong Kong researchers sequenced the virus from both of the man’s infections and found significant differences, suggesting the patient had been infected a second time.

The man’s first case was diagnosed March 26, and he had only mild symptoms.

He had no detectable antibodies after that first bout with the virus. He was positive again for the coronavirus on a saliva test Aug. 15 after a trip to Spain via the United Kingdom; the test was administered at the airport. The man had picked up a strain that was circulating in Europe in July and August, the researchers said.

It is still unclear how common reinfection from the new coronavirus might be.

Researchers said it is possible that in some people, a second exposure will prove more severe.