Relationship between average estimated occurrence of A. aegypti and A. albopictus in a country with the probability that CHIKV has ever been reported in that country. The probability of Aedes occurrence was calculated using existing estimates of mosquito distributions in 5-km x 5-km grid cells throughout the world 19. For each country, we calculated the human population-weighted average occurrence in the country (so mosquito levels in high density areas provided more weight than low density locations). The plot shows the proportion of countries that had ever reported CHIKV outbreaks for locations with a similar level of Aedes occurrence. We separately considered A. aegypti, A. albopictus and a 'Maximum', which is the maximum of either A. aegypti or A. albopictus in any location. The lines present the fit of a logistic regression model.
