Epidemic features and potential impact of vaccine campaigns on the 2025 chikungunya outbreak in southern China: a mathematical modelling study.

Chikungunya virus (CHIKV), an emerging arbovirus, is transmitted by Aedes mosquitoes. Climate change and increasing population mobility have driven recent outbreaks beyond traditional endemic regions. Since early July 2025, Guangdong province in southern China has faced an unprecedented outbreak of chikungunya fever. We aim to in-depth describe the epidemic features and theoretically assess the potential impact of vaccination campaigns. In total, the outbreak reported more than 25,000 cases. Foshan and Jiangmen successively emerged as epicenters of the outbreak. Through stringent public health interventions, the outbreak was controlled within two months in these two epicenters, respectively. Phylogenetic analysis revealed close genetic relation of the CHIKV isolates from this outbreak to the recent isolates in Réunion and Mayotte, but distant from the ones previously identified in China. Pre-emptive vaccination, achieving 20, 40%, 60%, and 80% coverage pre-outbreak, would avert up to 57%, 81%, 92%, and 97% infections shown by mathematical modelling, respectively. Achieving a daily vaccination rate comparable to the COVID-19 rollout, covering approximately 4% of the population in Foshan and 2% of the population in Jiangmen per day, could lower cumulative CHIKV infections by 68.7% in Foshan within two months and by 98.4% in Jiangmen within four months, respectively. In summary, the 2025 chikungunya outbreak in Guangdong was likely sparked by case importation. Implementation of stringent public health interventions is possible to control the outbreak, but can provoke significant public concerns. Vaccine campaigns are expected to be effective in both preparedness and response to future chikungunya outbreaks.