Scientists have reported an extreme case of a 72-year-old immunocompromised man who was infected with COVID-19 for 613 days. The virus mutated within his body, evading his immune system and evolving into a new immune-evasive variant. This case emphasizes the importance of protecting immunocompromised individuals from COVID-19 and other viral infections, as prolonged infections in these patients are more common and can lead to the emergence of new viral variants. Researchers are working to identify the best treatments for immunocompromised patients with persistent COVID-19 infections.