A 25-year-old was infected twice with the coronavirus earlier this year, scientists in Nevada have confirmed. It is the first confirmed case of so-called reinfection with the virus in the U.S. and the fifth confirmed reinfection case worldwide.
The cases underscore the importance of social distancing and wearing masks even if you were previously infected with the virus, and they raise questions about how the human immune system reacts to the virus.
The two infections in the Nevada patient occurred about six weeks apart, according to a case study published Monday in the medical journal The Lancet. The patient originally tested positive for the virus in April and had symptoms including a cough and nausea. He recovered and tested negative for the virus in May.
But at the end of May, he went to an urgent care center with symptoms including fever, cough and dizziness. In early June, he tested positive again and ended up in the hospital.
"The second infection was symptomatically more severe than the first," the authors of the study write. The patient survived his second bout with COVID-19.
This is the second confirmed case of coronavirus reinfection in which the patient was sicker the second time. A patient in Ecuador also suffered a more serious case of COVID-19 the second time they were infected with the virus.
Scientists are unsure why this might be. In theory, the body's immune system should make antibodies after the first infection that help it combat the virus more effectively if the person is exposed to the same virus again.
"There are many reasons why a person might get sicker the second time around," explains Akiko Iwasaki, a professor of immunobiology at Yale University who was not involved in the Nevada study. For example, "they may have been exposed to a lot higher levels of the virus the second time around," she says, or the immune response from the first infection might be making the disease worse rather than better.
But, she stresses, "this is all very speculative" because scientists still have very little information about the mechanisms at play.
One of the biggest outstanding questions is how widespread reinfection might be. It's difficult to confirm cases in which a person is infected twice. Scientists must have the nasal swabs from both the first and second infection in order to compare the genomes of both virus samples.
Only the most advanced hospital and laboratory facilities have the equipment and personnel to do the genome sequencing and analyze the results. As a result, most cases of reinfection are likely going undetected.
Danny Altmann, a professor of immunology at Imperial College London, says it seems that about 90% of people who have experienced "a clear, symptomatic infection" have the antibodies to fight off another infection, "perhaps for about a year."
"Of course, that leaves 10% who don't" have sufficient antibodies to fight off a second infection, he wrote in an email to NPR. "[T]hey have precisely the same risk as anyone out there, thus a small but significant number of reinfections."
The authors of the new study also raise the possibility that cases of people being infected multiple times could have implications for the efficacy of a coronavirus vaccine, since some people exposed to the virus may not be mounting sufficient immune responses to protect themselves from a second infection.
But Iwasaki says such cases have no bearing on the efficacy of a future vaccine. The virus can deploy proteins to get in the way of the immune response, whereas a vaccine has none of those proteins, she explains. "The good thing about a vaccine is that it can induce much better immunity, a much longer lasting immunity, than the natural exposure to the the virus," she says.
AILSA CHANG, HOST:
Scientists have confirmed that a Nevada man was infected with the coronavirus twice. It is the first confirmed reinfection in the U.S, and it underscores the importance of social distancing and wearing masks, even for survivors of COVID-19. NPR's Rebecca Hersher is here with more. Hey, Becky.
REBECCA HERSHER, BYLINE: Hey.
CHANG: Hey. So what do we know about this case in Nevada?
HERSHER: We actually know a lot. The patient is 25 years old from a county in Nevada that includes Reno. He tested positive for the virus in April at a community testing site. And he had some symptoms at that point, including a cough. And then, we know that he recovered. The symptoms went away. And in May, he tested negative. Now, here's where it gets strange. In late May, he got sick again. He went to an urgent care facility, told them he had a fever, dizziness and a cough. And it appears that they didn't test him for the coronavirus at that point, maybe because he had already had it. In any case, he went home. He got sicker. The first week of June, he ended up in the hospital with low oxygen levels, and he tested positive for the virus again.
CHANG: Wow. And how can we be sure that he was infected two separate times?
HERSHER: Right. So scientists at the University of Nevada had the nasal swabs from his tests, and they sequenced the genomes on the virus bits on the swabs - basically, fingerprinted them to see whether they were exactly the same or different enough to be two different infections. And they found that they appear to be two different infections. So this is the first confirmed case of so-called reinfection by the coronavirus in the U.S. It's the fifth such case in the world. And there are a handful more that are suspected to be reinfections, but they haven't been confirmed with this kind of genetic testing.
CHANG: OK, so five confirmed reinfection cases like this worldwide. I guess my first thought is that doesn't sound like very many compared to the scale of this pandemic as a whole.
HERSHER: Right. You know, getting the coronavirus multiple times appears to be rare, although it's hard to know exactly how widespread this is because you need the genetic testing capabilities and the testing swabs from both the first and the second infection.
HERSHER: So probably there are people who have been infected twice, and it's flying under the radar.
CHANG: And do we know anything from this case, about why this might happen to some people versus others?
HERSHER: That is the million-dollar question. So, of course, immune system 101 is that a virus comes in, it triggers an immune response and the immune system creates antibodies - right? - that remember the virus and attack it if it shows up again in the future. So why didn't this happen in these patients? And the scientists I spoke to today, they said maybe the person was exposed to a much bigger dose of the virus the second time, or it's possible the immune response was more harmful than helpful the second time around. But honestly, those are just theories. Scientists say they need a lot more than five confirmed cases to really understand what's happening here.
CHANG: Right. Well, what does this mean ultimately for people's lives? Like, should we be adjusting our behavior as it becomes more clear that some people can be infected more than once?
HERSHER: That's a good question, right? And one thing that I think some people who have had COVID-19 and recovered from it might think is that they don't need to worry about the virus, but that's not really the case. And I asked Akiko Iwasaki, an immunobiologist at Yale University, about this.
AKIKO IWASAKI: What the reinfection cases emphasize is that even if you recovered first from infection, there's no guarantee that you won't be infected again, or you won't be transmitting the virus again during that reinfection.
HERSHER: So she says that means that everyone should be social distancing and wearing masks and washing their hands, even if you've already been infected with the virus in the past, even if you've survived COVID-19. And I think that's counterintuitive for a lot of people, but she says it's really important.
CHANG: That is NPR science reporter Rebecca Hersher. Thank you, Becky.
HERSHER: Thanks so much. Transcript provided by NPR, Copyright NPR.