Contracting Covid-19 may not necessarily protect against future infection, a new study reveals.
The second infection can occur within a short time frame and be even more severe.
In the first study to confirm a case of Covid-19 reinfection in the USA, researchers found evidence that an individual with no known immune disorders or underlying conditions was infected on two separate occasions.
According to a case study published in The Lancet Infectious Diseases journal, the patient, a 25-year-old male living in Washoe County, Nevada, was infected with two distinct Covid variants within a 48-day time-frame, while testing negative in between infections.
At least four other reinfection cases have been confirmed globally in Belgium, the Netherlands, Hong Kong, and Ecuador.
However, only the Ecuador reinfection case displayed worse disease outcomes than the first infection.
The US patient's second infection was more severe, resulting in hospitalisation with oxygen support, indicating previous exposure to Covid-19 may not translate to guaranteed immunity, but further research into reinfections is required.
The authors note that all individuals - whether previously diagnosed or not - should take identical precautions to prevent infection with Covid-19.
After testing positive for SARS-CoV-2 in April 2020, the patient tested negative for the virus on two separate occasions. In June 2020, after experiencing severe symptoms, including fever, headache, dizziness, cough, nausea, and diarrhoea, the patient was hospitalized and tested positive for a second time.
The patient has since been discharged from the hospital and has recovered from the second infection. A full timeline is available in the paper.
"There are still many unknowns about Covid infections and the immune system's response, but our findings signal that a previous Covid infection may not necessarily protect against future infection," said Mark Pandori, of the Nevada State Public Health Laboratory at the University of Nevada, Reno School of Medicine and lead author of the study.
"It is important to note this is a singular finding and does not provide generalizability of this phenomenon.
"While more research is needed, the possibility of reinfections could have significant implications for our understanding of Covid-19 immunity, especially in the absence of an effective vaccine.
"It also strongly suggests that individuals who have tested positive should continue to take serious precautions when it comes to the virus, including social distancing, wearing face masks, and hand washing.
"We need more research to understand how long immunity may last for people exposed to SARS-CoV-2 and why some second infections, while rare, are presenting as more severe.
"So far, we've only seen a handful of reinfection cases."