Interactions between timing and transmissibility explain diverse flavivirus dynamics in Fiji

Area of Science:

• Epidemiology
• Virology
• Mathematical Modeling

Background:

• Zika virus (ZIKV) exhibits diverse transmission patterns, ranging from brief, large outbreaks to prolonged low-level persistence.
• Understanding the factors driving these varied dynamics is crucial, especially when comparing ZIKV with similar mosquito-borne flaviviruses like dengue.
• Fiji has experienced significant dengue epidemics and showed evidence of multi-year ZIKV transmission between 2013 and 2017.

Purpose of the Study:

• To investigate the factors contributing to the observed multi-year transmission of Zika virus in Fiji.
• To differentiate the transmission dynamics of ZIKV from other closely related mosquito-borne flaviviruses.
• To develop and apply a robust modeling framework to analyze complex epidemiological data.

Main Methods:

• Jointly fitting a transmission dynamic model to multiple data sources: surveillance, serological, and molecular data.
• Utilizing mathematical modeling to simulate and analyze ZIKV transmission patterns.
• Comparing transmission dynamics across different flaviviruses in the Fijian context.

Main Results:

• Two primary factors were identified as critical for ZIKV's multi-year persistence in Fiji: strong seasonal effects creating an optimal outbreak period, and ZIKV introductions occurring after this optimal window.
• These factors explain how ZIKV transmission could extend across multiple seasons.
• The modeling approach successfully captured the observed transmission dynamics.

Conclusions:

• The study elucidates the specific ecological and temporal factors enabling sustained Zika virus transmission in Fiji.
• The findings provide insights into why ZIKV may persist longer than initially expected or observed in other settings.
• The methodology of jointly fitting models to diverse data sources offers a valuable approach for understanding outbreak dynamics of infectious diseases globally.