A 25-year-old man in the US has caught Covid twice, a study published in the Lancet Infectious Diseases journal showed, indicating exposure to the virus may not translate to total immunity.

According to the Lancet, it is the first confirmed case of a US patient becoming re-infected with Covid-19, and the fifth known case reported worldwide.

In a case study, the patient from Washoe County in Nevada, had two positive tests for SARS-CoV-2, the first on April 18, 2020, and the second on June 5, 2020, separated by two negative tests done during follow-up in May 2020.

"Genomic analysis of SARS-CoV-2 showed genetically significant differences between each variant associated with each instance of infection. The second infection was symptomatically more severe than the first," the study authors from the University of Nevada, wrote.

The researchers revealed that the patient presented to a community testing event held by the Washoe County Health District on April 18, 2020.

He had symptoms consistent with viral infection (sore throat, cough, headache, nausea, and diarrhoea), which had started on March 25.

The patient had no history of clinically significant underlying conditions, and no indications of compromised immunity were identified.

During isolation, the patient's symptoms resolved (reported on April 27, 2020) and he continued to feel well until May 28, 2020.

On May 31, 2020, the patient sought care at an urgent care centre with self-reported fever, headache, dizziness, cough, nausea, and diarrhoea, at which time chest radiography was done and he was discharged home.

Five days later (on June 5, 2020), the patient presented to a primary care doctor and was found to be hypoxic with shortness of breath. He was instructed to go to the emergency department after the provision of oxygen.

"Genetic discordance of the two SARS-CoV-2 specimens was greater than could be accounted for by short-term in vivo evolution," the researchers wrote.

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.

"All individuals, whether previously diagnosed with Covid-19 or not, should take identical precautions to avoid infection with SARS-CoV-2. The implications of reinfections could be relevant for vaccine development and application," they noted.

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