Quantifying the risk of Zika virus spread in Asia during the 2015-16 epidemic in Latin America and the Caribbean: A modeling study

Abstract

Background: No large-scale Zika epidemic has been observed to date in Southeast Asia following the 2015-16 Latin American and the Caribbean epidemic. One hypothesis is Southeast Asian populations' partial immunity to Zika.

Method: We estimated the two conditions for a Zika outbreak emergence in Southeast Asia: (i) the risk of Zika introduction from Latin America and the Caribbean and, (ii) the risk of autochthonous transmission under varying assumptions on population immunity. We also validated the model used to estimate the risk of introduction by comparing the estimated number of Zika seeds introduced into the United States with case counts reported by the Centers for Disease Control and Prevention (CDC).

Results: There was good agreement between our estimates and case counts reported by the CDC. We thus applied the model to Southeast Asia and estimated that, on average, 1-10 seeds were introduced into Indonesia, Malaysia, the Philippines, Singapore, Thailand and Vietnam. We also found increasing population immunity levels from 0 to 90% reduced probability of autochthonous transmission by 40% and increasing individual variation in transmission further reduced the outbreak probability.

Conclusions: Population immunity, combined with heterogeneity in transmission, can explain why no large-scale outbreak was observed in Southeast Asia during the 2015-16 epidemic.

Keywords: Asia; Disease transmission; Epidemics; Infectious; Latin America; Southeastern; Zika virus.

Fig. 1

Estimated mean number of ZIKV introductions from Latin America and Caribbean into each state in the United States (black dots) and ZIKV case counts from the United States Centers for Disease Control and Prevention dataset (red dots). Black bars denote the 95% confidence interval. AL: Alabama, AZ: Arizona, AR: Arkansas, CA: California, CO: Colorado, CT: Connecticut, DE: Delaware, DC: District of Columbia, FL: Florida, GA: Georgia, HI: Hawaii, ID: Idaho, IL: Illinois, IN: Indiana, IA: Iowa, KS: Kansas, KY: Kentucky, LA: Louisiana, ME: Maine, MD: Maryland, MA: Massachusetts, MI: Michigan, MN: Minnesota, MS: Mississippi, MO: Missouri, MT: Montana, NE: Nebraska, NV: Nevada, NH: New Hampshire, NJ: New Jersey, NM: New Mexico, NY: New York, NC: North Carolina, ND: North Dakota, OH: Ohio, OK: Oklahoma, OR: Oregon, PA: Pennsylvania, RI: Rhode Island, SC: South Carolina, SD: South Dakota, TN: Tennessee, TX: Texas, UT: Utah, VT: Vermont, VA: Virginia, WA: Washington, WV: West Virginia, WI: Wisconsin, WY: Wyoming. [color should be used in print]. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

Fig. 2

Estimated mean number of potential seeds introduced from Latin America and Caribbean into each Southeast Asian country (black dots). Black bars denote the 95% confidence interval.

Fig. 3

Estimated probabilities of autochthonous transmission in Indonesia, Malaysia, the Philippines, Singapore, Thailand and Vietnam assuming independent introductions of the estimated mean number of potential seeds at varying population immunity levels. Lines denote the estimated average probabilities of autochthonous transmission and the shaded areas denote the 95% confidence interval. Red, black and blue colors respectively denote the high, moderate and low transmissibility scenarios. [color should be used in print]. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)