Latitudinal patterns and environmental correlates of global COVID-19 incidence rates

Background Geographical location—particularly latitude—played a critical role in shaping the spatial distribution of global COVID-19 incidence rates (IR). However, inconsistencies in temporal coverage and spatial scope across previous studies led to ongoing debate regarding the association between IR and latitude. Methods Based on a broader global dataset, and following the principles of relatively even spatial distribution, consistent unit size, and complete epidemiological records, this study selected 173 units across 62 countries. A Generalized Additive Model (GAM) was used to systematically analyze the relationships among COVID-19 IR, latitude, and associated environmental factors from March 1, 2020, to February 28, 2022. Results IR consistently increased with latitude across the three major pandemic waves and throughout the entire study period. A minimum IR occurred near 20° latitude (15°–25°). Further analyses indicated that this latitude zone was characterized by average temperature (22.1 ± 5.6 °C), relative humidity (66.8 ± 10.3%), ultraviolet radiation (98.6 ± 9.2 kJ/m 2 ), diurnal temperature range (9.4 ± 4.2 °C), and cloud cover (50.9 ± 5.2%)—a combination aligning with optimal climatic comfort for humans. Conclusion A nonlinear latitudinal pattern in COVID-19 IR was identified, with the lowest incidence consistently observed around 20° latitude (15°–25°). This pattern may reflect environmental gradients associated with latitude. These findings highlight a stable geographic structure of COVID-19 distribution and indicate that regionally differentiated environmental contexts may be relevant for informing public health preparedness.