Coronavirus reinfections are real but very, very rare

REPORTS of reinfection with the coronavirus evoke a nightmarish future: Repeat bouts of illness, impotent vaccines, unrelenting lockdowns — a pandemic without an end.

A case study published Monday, about a 25-year-old man in Nevada, has stoked those fears anew. The man, who was not named, became sicker the second time that he was infected with the virus, a pattern the immune system is supposed to prevent.

But these cases make the news precisely because they are rare, experts said: More than 38 million people worldwide have been infected with the coronavirus, and as of Monday, fewer than five of those cases have been confirmed by scientists to be reinfections.

“That’s tiny — it’s like a microlitersized drop in the bucket, compared to the number of cases that have happened all over the world,” said Angela Rasmussen, a virologist at Columbia University in New York.

In most cases, a second bout with the virus produced milder symptoms or none at all. But for at least three people, including one patient in Ecuador, the illness was more severe the second time around than during the first infection. An 89-year-old woman in the Netherlands died during her second illness.

Rare as these cases may be, they do indicate that reinfection is possible, said Akiko Iwasaki, an immunologist at Yale University, who wrote a commentary accompanying the Nevada case study, published in The Lancet Infectious Diseases.

“It’s important to note that there are people who do get reinfected, and in some of those cases you get worse disease,” Ms. Iwasaki said. “You still need to keep wearing masks and practice social distancing even if you have recovered once from this infection.”

We asked experts what is known about reinfections with the coronavirus, and what the phenomenon means for vaccinations and the course of the pandemic.

REINFECTION WITH THE CORONAVIRUS IS AN UNUSUAL EVENT

First, the good news: Reinfection seems to be vanishingly rare.

Since the first confirmed case of reinfection, reported in Hong Kong on Aug. 24, there have been three published cases; reports of another 20 await scientific review.

But it is impossible to know exactly how widespread the phenomenon is. To confirm a case of reinfection, scientists must look for significant differences in the genes of the two coronaviruses causing both illnesses.

In the United States, where testing was a rare resource much of this year, many people were not tested unless they were sick enough to be hospitalized. Even then, their samples were usually not preserved for genetic analysis, making it impossible to confirm suspected reinfections.

A vast majority of people who do get reinfected may go undetected. For example, the man in Hong Kong had no symptoms the second time, and his infection was discovered only because of routine screening at the airport.

“There are a lot of people that are going to also have been exposed that aren’t having symptoms, that we’re never going to hear about,” said Marion Pepper, an immunologist at the University of Washington in Seattle.

People whose second infections are more severe are more likely to be identified, because they return to the hospital. But those are likely to be even rarer, experts said.

“If this was a very common event, we would have seen thousands of cases,” Ms. Iwasaki said.