A COVID-19 patient in Nevada is thought to be the first person in the U.S. to catch the coronavirus twice.
The unnamed 25-year-old individual from Reno tested positive for the coronavirus that causes COVID-19 on April 18, and had symptoms including a sore throat, headache, nausea, and diarrhea, according to a pre-print study. By April 27 the symptoms had resolved, and two coronavirus tests came back negative on May 9.
On 31 May, the patient reported having a fever, headache, feeling dizzy, as well as a cough, nausea and diarrhea. Five days later, the patient was hospitalized after their condition worsened, and tested positive for the coronavirus again. Samples from the patient also showed they had antibodies against the coronavirus.
The patient did not have any immune problems that might explain reinfection, and they were not taking immunosuppressant drugs the team said.
The data supports "an instance of reinfection with SARS-CoV-2 [the coronavirus]," according to the researchers. But they said: "this may represent a rare event."
The scientists examined the genetic make-up of the virus found in the patient's samples, and found they were different enough to suggest they were infected twice.
Scientists worked with the Washoe County Sheriff's Office Forensic Sciences Unit to carry out identity tests on the samples to verify they were from the same patient.
The findings were submitted as a pre-print to the website SSRN meaning it has not been through the rigorous peer review process required to publish in scientific journals. Releasing studies this way enables scientists to prompt debate on a topic and this approach is particularly useful in fast-moving situation like a pandemic.
Mark Pandori, director of the Nevada State Public Health Laboratory, said in a statement: "It is just one finding, but it shows that a person can possibly become infected with SARS-CoV-2 a second time. If reinfection is possible on such a short timeline, there may be implications for the efficacy of vaccines developed to fight the disease. It may also have implications for herd immunity."
However he said it was important to note that is a single finding, and does not provide information on whether this is likely to occur again.
Over half a year into the COVID-19 pandemic, many unknowns remain, including how long immunity to the virus lasts. Evidence on other members of the coronavirus family of viruses suggest immunity can last for one to three years, according to the authors.
Pandori said: "After one recovers from COVID-19, we still do not know how much immunity is built up, how long it may last, or how well antibodies play a role in protection against a reinfection. This is a novel disease. We still have a steep learning curve ahead and lots of work to do, especially as inconvenient truths arise."
The incident comes after a man in Hong Kong tested positive for the coronavirus for a second time, four and a half months after first getting COVID-19. The marked the first documented case of coronavirus reinfection. Two other cases of re-infection were also reported this week, one in Belgium and another in the Netherlands.
Daniel Davis, professor of immunology at the University of Manchester, U.K., who was also not involved in the study, told Newsweek the Nevada case was similar to that in Hong Kong. "On the face of it, this shows that someone can be infected with SARS-CoV-2, recover, and then be infected again. But these individual case reports do not give any indication of how likely this is," he said.
Davis said it is to be expected that people will be exposed to this virus more than once.
"What is important to know is whether or not their immune system has built up some protection from the first infection to stop them becoming ill from the second infection and whether or not they still transmit the virus to others. In this new case, the second infection did cause symptoms. An immune response against a second infection may cause some symptoms such as a fever, but it's of some concern that this patient was hospitalised after a second infection.
"Importantly however, it's hard to make any general conclusions from this study of one individual."
More research is needed, following large numbers of people over time, Davis said, in order to paint a "general picture of what happens to people exposed to SARS-CoV-2 for a second time."
Ian Jones, professor of virology at the U.K.'s University of Reading who also did not work on the study, told Newsweek the Nevada case "fits our current understanding that some individuals seem not to mount an effective immune response to a first infection leaving them susceptible to a second.
Addressing concerns that such cases may mean vaccines could not be used to control the pandemic, Jones said such preparations "are purposefully designed to produce an immune response in all cases, very different to the real infection."
Jones said such cases seem to be "rare" and something "to note but not to overplay."
Julian W Tang, honorary associate professor of respiratory sciences at the University of Leicester who also did not work on the case, told Newsweek: "Undoubtedly we will see more of such cases over the coming months—with more robust definitions of what constitutes reinfection—to understand this phenomenon better—including the potential impact on any SARS-CoV-2 vaccine."
Jeremy Rossman, honorary senior lecturer in virology at the University of Kent told Newsweek: "We do not yet know enough about reinfections to make any conclusions. However, it is recommended that even people that have been infected with COVID-19 continue to practice the recommended precautions—physical distancing, [wearing] face coverings and hand washing— to ensure that they are protected against any potential reinfections."
Discussing the possibility of reinfection in March, Benjamin Linas, an expert in infectious diseases at Boston Medical Center and Boston University, told Newsweek: "Perhaps there is something special or different about those individuals [infected twice]. Maybe they have immune system suppression, maybe they take medicines that somehow make them more susceptible to re-infection. We do not know yet.
"For example, it may be true that people can be re-infected with SARS-CoV-2, but that the second time around the infection is less serious, because there is some partial immunity."
This article has been updated with comment from Daniel Davis, Ian Jones, Julian Tang, and Jeremy Rossman.