Coronavirus: First confirmed case of reinfection reported in Hong Kong

Researchers say man had no Covid-19 symptoms the second time, suggesting immune system kept virus somewhat in check

A 33-year-old man was infected a second time with the coronavirus more than four months after his first bout in 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. 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 at the request of the New York Times. “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, Ms 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,” Ms 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.

“I believe this is the first reported case that is confirmed by genome sequencing,” said Dr Kelvin Kai-Wang To, a clinical microbiologist at the University of Hong Kong.

The study is to be published in the journal Clinical Infectious Diseases.

The man’s first case was diagnosed March 26th, and he had only mild symptoms. In accordance with regulations in Hong Kong, he was hospitalised on March 29th even though his symptoms had subsided and was released on April 14th only after he had tested negative for the virus twice.

The man had no detectable antibodies after that first bout with the virus. He was positive again for the coronavirus on a saliva test on August 15th 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.

His infections were clearly caused by different versions of the coronavirus, Dr To said. “Our results prove that his second infection is caused by a new virus that he acquired recently, rather than prolonged viral shedding.”

Common cold coronaviruses are known to cause reinfections in less than a year, but experts had hoped the new coronavirus might behave more like its cousins – severe acute respiratory syndrome and Middle East respiratory syndrome – which seemed to produce protection lasting a few years.

It is still unclear how common reinfection from the new coronavirus might be because few researchers have sequenced the virus from each infection. “We’ve had, what, 23 million cases documented thus far, but the fact that one out of them at this point has been reinfected should not cause undue alarm as of yet,” said Jeffrey Shaman, an epidemiologist at Columbia University in New York.

“However, it remains very, very concerning – and this does nothing to dispel that – that we may be subject to repeat infection with this virus,” he said.

Ms Iwasaki was more sanguine, however. She noted the man had no antibodies after the first infection but produced them after the second exposure. Immunity is expected to build with each exposure to a pathogen exactly in this way, she noted.

“Again, it’s what the textbook says should happen,” she said. “When you have second exposure to the same pathogen, you should elevate the antibody, and that’s what’s happening.” – New York Times