Assessing vulnerability for future Zika virus outbreaks using seroprevalence data and environmental suitability maps

Area of Science:

• Epidemiology
• Public Health
• Environmental Health

Background:

• The 2015-17 Zika virus (ZIKV) epidemic in the Americas ended unexpectedly, with evolving population immunity hypothesized as the cause.
• Herd immunity, typically achieved at 60-70% seroprevalence, was only observed in limited South American areas, suggesting widespread vulnerability.

Purpose of the Study:

• To assess population vulnerability to ZIKV by comparing environmental suitability for transmission with documented seroprevalence.
• To identify geographic areas at high risk for future ZIKV outbreaks based on observed-expected seroprevalence discrepancies.

Main Methods:

• A systematic literature search identified 119 locations with seroprevalence and geospatial data from 37 studies.
• Environmental suitability for ZIKV transmission was assessed for each location.
• Observed seroprevalence was compared to a hypothetical expected seroprevalence to determine vulnerability levels (high, low, very low risk).

Main Results:

• Of 119 locations, 69 (58%) were categorized as high risk, 47 (39%) as low risk, and 3 (3%) as very low risk for ZIKV outbreaks.
• Significant heterogeneity exists between environmental suitability and observed seroprevalence, indicating potential population vulnerability.
• Vulnerability was particularly noted in areas at the environmental suitability fringes, such as Sao Paulo, Brazil.

Conclusions:

• Discrepancies between expected and observed ZIKV seroprevalence suggest large populations remain vulnerable to future outbreaks.
• The reasons for the rapid subsidence of the ZIKV epidemic despite unaffected populations remain unclear.
• Predicting future ZIKV outbreaks with confidence is challenging due to the current lack of understanding regarding epidemic dynamics and population immunity.