Hospital-acquired COVID-19 was a major concern, particularly during the early phases of the pandemic when population immunity was low. This study includes nearly 304,000 patients in Sweden, divided into two timeframes within the pandemic. Nosocomial infection rates were low across both time frames, but 30-day mortality was higher (compared to patients without infection) in the first timeframe when immunity was low. During the second timeframe when vaccination levels were higher, there was no difference in 30-day mortality rates between patients with or without nosocomial infections.