OBJECTIVES:

CHIKV is transmitted by Aedes aegypti and Aedes albopictus. The disease is characterized by high morbidity and debilitating long-term sequalae. The global spread of CHIKV has been facilitated by viral adaptation to new vectors and expansion of mosquito habitats due to climate change, posing increased outbreak risks in temperate regions after importation of CHIKV. This study assessed the transmission dynamics and effectiveness of vaccination as an intervention strategy in the event of an CHIKV outbreak.

METHODS:

A human-mosquito SEIR model was employed to replicate the transmission dynamics of the 2017 CHIKV outbreak in Anzio and simulate a hypothetical outbreak in Rome. The model incorporated mosquito population dynamics, accounting for the mosquito life-cycle stages and temperature dependencies. The primary outcome measure was the number of infections in two scenarios: with and without vaccination. Different levels of vaccine coverage were tested to evaluate their impact on infection rates.

RESULTS:

Without intervention and given the current environmental circumstances, a local CHIKV outbreak in Rome could affect 15.05% of the population, resulting in 413,607 infections. To illustrate the potential impact of climate change, an increase of 1-degree Celsius was applied in the model, leading to an infection rate of 81.38% among the local population. Assuming the vaccine effectiveness of 98.9% based on phase 3 seroprotection data, vaccination with VLA1553 could prevent two-thirds of infections with a coverage rate of 20%. Increasing the coverage to 40% resulted in a 90% reduction in infections. The timing of vaccine deployment and the time-to-immunity were considered in the analysis.

CONCLUSIONS:

The impact of a potential CHIKV outbreak in Rome showed to be considerable, especially in a future climate change scenario. The study highlights that in the event of a CHIKV outbreak, intervention with vaccination deployed in a timely manner would be highly effective in preventing a significant disease burden.