Scientists have confirmed the first case of coronavirus reinfection in the United States: a 25-year-old Nevada man whose second round of the virus was more severe than the first.
The findings were published Monday in the medical journal The Lancet.
The man, who remains unnamed, first tested positive in April before recovering and testing negative in May. Then in June, he tested positive for the virus again, developing symptoms of COVID-19 a second time.
According to the case study, his second infection was more severe than the first, with symptoms including fever, cough and dizziness.
The researchers sequenced the RNA from both virus samples and found they were two different strains, making it a true reinfection.
Scientists have not concluded why someone might contract the virus twice or if some people are more predisposed to reinfection. The Nevada case marks the fifth case globally of reinfection, and scientists say so far that such instances are rare.
Yale University immunobiology professor Akiko Iwasaki told NPR a second positive test could happen for a number of reasons, such as being exposed at higher levels to the virus or an immune response making the virus seem worse rather than better the second time around.
Generally, researchers are finding that people who get COVID-19 develop a healthy immune response, but it’s unknown how long it lasts.
The case study was first sent to The Lancet in August, but it was officially published and the case was confirmed as the first U.S. reinfection this week.