Lifestyle Health 25-Year-Old Nevada Man Infected Twice with COVID, Scientists Confirm The man's infections happened about six weeks apart and his second case was more severe, requiring hospitalization By Julie Mazziotta Julie Mazziotta Twitter Julie Mazziotta is the Sports Editor at PEOPLE, covering everything from the NFL to tennis to Simone Biles and Tom Brady. She was previously an Associate Editor for the Health vertical for six years, and prior to joining PEOPLE worked at Health Magazine. When not covering professional athletes, Julie spends her time as a (very) amateur athlete, training for marathons, long bike trips and hikes. People Editorial Guidelines Published on October 13, 2020 01:37 PM Share Tweet Pin Email Trending Videos Doctor performing nose swab test. Photo: Getty A 25-year-old man in Nevada was infected with COVID-19 twice, scientists confirmed, marking the first definite case of reinfection in the U.S. and the fifth worldwide. The resident from Washoe County, who had no history of preexisting conditions or known immune disorders, first tested positive for COVID-19 on April 18 and experienced mild symptoms, including fever, dizziness and coughing. His symptoms abated and he tested negative twice in May, but about six weeks after his first infection, he started feeling sick again. The man went to an urgent care center at the end of May, again dealing with fever, dizziness and coughing, and tested positive in early June. 33-Year-Old Man in Hong Kong Found to Have the First Confirmed Case of Coronavirus Reinfection The man’s second infection “was symptomatically more severe than the first,” wrote the scientists who studied his case for a study published in the journal Lancet, and he needed to be hospitalized for shortness of breath. He has since recovered and returned home from the hospital. There have been five confirmed cases of COVID-19 reinfection in other countries and anecdotal cases in the U.S., but this is the first definite American case. It emphasizes that immunity from COVID-19 is not certain, and even those who have recovered from the virus are at risk of contracting it again. WHO Warns That Antibody Testing Does Not Ensure Immunity: ‘There Is Not Enough Evidence’ The scientists said that the Nevada man contracted COVID-19 on two separate occasions, and confirmed that his second illness was not the original infection coming back again. His two infections had “significant differences” in their genetic codes. RELATED VIDEO: Amanda Kloots, Widow of Nick Cordero, Calls Trump ‘Disgraceful’ for Minimizing Deadly Coronavirus “These findings suggest that the patient was infected by SARS-CoV-2 on two separate occasions by a genetically distinct virus. Thus, previous exposure to SARS-CoV-2 might not guarantee total immunity in all cases,” the study authors wrote. Dallas Woman Tests Positive for Coronavirus Again After 4 Months: 'I Was Floored' Still, cases of reinfection are rare, and current research shows that the majority of people develop antibodies that should help them avoid reinfection, or at least have a better immune response to fight the virus. The study authors said that their findings from this man’s case show that everyone, regardless of if they have already had COVID-19, should continue wearing masks, hand washing and social distancing. “All individuals, whether previously diagnosed with COVID-19 or not, should take identical precautions to avoid infection with SARS-CoV-2,” they said. As information about the coronavirus pandemic rapidly changes, PEOPLE is committed to providing the most recent data in our coverage. Some of the information in this story may have changed after publication. For the latest on COVID-19, readers are encouraged to use online resources from the WHO and local public health departments. PEOPLE has partnered with GoFundMe to raise money for the COVID-19 Relief Fund, a GoFundMe.org fundraiser to support everything from frontline responders to families in need, as well as organizations helping communities. For more information or to donate, click here.