A Nevada man appears to be the nation's first confirmed case of COVID-19 reinfection, researchers say.
The case is detailed in an online preprint, a study that has not yet been peer reviewed before officially being published.
The case involves a 25-year-old man living in Reno, Nevada, who first tested positive for COVID-19 in mid-April. He recovered, but got sick again in late May. The second time around, his illness was more severe, the case report said.
Researchers at the University of Nevada, Reno School of Medicine and the Nevada State Public Health Laboratory reported that genetic sequencing of the virus revealed that he had been infected with a slightly different strain, indicating a true reinfection.
Reinfection with the coronavirus appears to be rare. This is the first case reported among the nation's nearly 6 million cases so far.
"The evidence so far suggests that if you've been infected and recovered, then you're protected for some period of time," Dr. Ashish Jha, director of the Harvard Global Health Institute, said. "We don't know how long, and we're going to find individual cases of people for whom that's not true."
Indeed, on Monday, a case of COVID-19 reinfection was reported in Hong Kong — the first such confirmation of reinfection during the pandemic. Two European patients, one in Belgium and one in the Netherlands, were also reported this week to have been reinfected with the virus.
But in those instances, the patients did not get sick the second time around, or they developed much milder forms of the illness than their first infection.
"You'd expect the second time around people to have much milder or ideally no symptoms," Jha said. That's because the immune system should be able to mount a more robust response, and the Hong Kong case was "completely consistent with that."
In the Nevada case, however, the man got sicker the second time. When he was first infected, he had typical symptoms for the coronavirus: headache, cough, sore throat, nausea and diarrhea. Within about 10 days, the symptoms cleared up, and he tested negative for the virus.
But a month later, on May 28, he started feeling sick again, experiencing dizziness as well as the previous symptoms.
The illness did not clear up quickly this time. Within a week, his blood oxygen level fell dangerously low. He needed help breathing, and was hospitalized. Once again, the man tested positive for SARS-CoV-2, the virus that causes COVID-19.
"That's very concerning," Dr. William Schaffner, an infectious disease expert at Vanderbilt University Medical Center in Nashville, said.
"If this sort of reinfection is common, then we have to worry about how strong the protection will be that we get vaccines," Schaffner said.
If reinfection were common, however, "we would have seen it," Jha said. "There's so much disease in our country."