Longitudinal Analysis of Italian COVID-19 Mortality: Seasonal Effects and Trend Evolution from September 2021 to September 2024, Including 2025 Updates

Earlier research (2021–2024, Omicron and post Omicron dominant period) established a pronounced seasonal pattern in Italian COVID-19 deaths, with weekly mortality spiking in early winter after increases throughout summer and fall, with a subsequent decline in the late winter and spring periods. Using recent data spanning 53 weeks (late May 2024–late May 2025), a new investigation utilizing piecewise linear regression confirms the continuation of this trend. The data shows the cycle repeating precisely: mortality rose in early summer, peaked at the beginning of wither, and declined steadily through midwinter and spring, tracking the previous year’s trend. This persistence suggests a continued influence of the seasonal trend on COVID-19 mortality, necessitating further exploration into the driving factors.