A man in France is critically ill with the coronavirus variant first identified in South Africa four months after he was previously infected with the virus — the first recorded reinfection case involving the contagious mutation, according to his doctors.

After experiencing a mild infection in September, the 58-year-old man with a history of asthma was hospitalized last month and remains in critical condition, according to a paper shared Friday by the journal Clinical Infectious Diseases. The authors wrote that cases of reinfection like this “remain rare albeit probably underestimated,” urging further investigation into cross-immunity between variants and the effectiveness of vaccines against them.

The news comes as reports of the variant, called B. 1.351, have escalated globally, including 13 cases in five states, according to the U.S. Centers for Disease Control and Prevention. With the increased prevalence of the mutation, scientists have expressed concern that the variant, and two others first identified in the United Kingdom and Brazil, may become a predominant source of infection and elude coronavirus vaccines developed before the variants were detected.