A 33-year-old man was contaminated a second time with the coronavirus greater than 4 months after his first bout, the primary documented case of so-called reinfection, researchers in Hong Kong reported Monday.

The discovering was not surprising, particularly given the tens of millions of people that have been contaminated worldwide, specialists stated. And the person had no signs the second time, suggesting that despite the fact that the prior publicity didn’t forestall the reinfection, his immune system saved the virus considerably in verify.

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

People who would not have signs should still unfold the virus to others, nonetheless, underscoring the significance of vaccines, Dr. Iwasaki stated. In the person’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,” Dr. Iwasaki stated.

Doctors have reported a number of instances of presumed reinfection in the United States and elsewhere, however none of those cases have been confirmed with rigorous testing. Recovered individuals are recognized to hold viral fragments for weeks, which may result in constructive take a look at outcomes in the absence of dwell virus.

But the Hong Kong researchers sequenced the virus from each of the person’s infections and located important variations, suggesting that the affected person had been contaminated a second time.

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

The examine is to be revealed in the journal Clinical Infectious Diseases. The Times obtained the manuscript from the college.

The man’s first case was identified on March 26, and he had solely delicate signs. In accordance with laws in Hong Kong, he was hospitalized on March 29 despite the fact that his signs had subsided, and launched on April 14 solely after he had examined unfavorable for the virus twice.

He had no detectable antibodies after that first bout with the virus. He was constructive once more for the coronavirus on a saliva take a look at on Aug. 15 after a visit to Spain by way of the United Kingdom; the take a look at was administered on the airport. The man had picked up a pressure that was circulating in Europe in July and August, the researchers stated.

His infections had been clearly brought on by completely different variations of the coronavirus, Dr. To stated: “Our results prove that his second infection is caused by a new virus that he acquired recently, rather than prolonged viral shedding.”

Common chilly coronaviruses are recognized to trigger reinfections in lower than a 12 months, however specialists had hoped that the brand new coronavirus would possibly behave extra like its cousins SARS and MERS, which appeared to supply safety lasting a number of years.

It’s nonetheless unclear how frequent reinfection from the brand new coronavirus could be, as a result of few researchers have sequenced the virus from every an 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,” stated 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 stated.

Dr. Iwasaki was extra sanguine. She famous that the person had no antibodies after the primary an infection however produced them after the second publicity. Immunity is anticipated to construct with every publicity to a pathogen precisely in this fashion, she famous.

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

Most people who find themselves contaminated with the coronavirus produce detectable antibodies that may be anticipated to guard in opposition to the virus. Even individuals who had solely delicate signs, together with this man, might also have immune “memory” in the type of B and T cells that forestall signs on second publicity.

“The majority of patients likely have a cocktail of immune responses that activate on second exposure,” stated Brian Wasik, a virologist at Cornell University. “This Hong Kong patient also seems to have been asymptomatic on second infection, perhaps due to some immune response.”

But the researchers stated it’s additionally attainable that in some individuals, a second publicity will show extra extreme. “It cannot be generalized yet, because there’s still a possibility that the second infection can be worse,” Dr. To stated.

Building immune reminiscence is just not not like boosting reminiscence of an individual, stated Dr. Michael Mina, an immunologist on the Harvard T.H. Chan School of Public Health.

The preliminary bout with the brand new coronavirus is prone to outcome in “non-sterilizing immunity,” however the virus will elicit a stronger response with every publicity, he stated: “It is often these second and third exposures that help to solidify the memory response for the long term.”

Over all, specialists stated, it’s unclear how usually individuals would possibly turn out to be reinfected, and the way quickly, after a primary bout with the virus.

“Those remain open questions, because one person exhibiting a mild reinfection, clearly documented as a distinct strain of the virus, does not provide enough evidence one way or another,” Dr. Shaman stated.

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