“They found that the introduction of the infected mosquitoes into local mosquito populations was “associated with a significant reduction” in dengue of up to 97% in each city compared to ten years prior to the start of the experiment.”
The headline number is 97%, measured against the decade before. The controlled study in Medellín found 47%. That is still a big result for a disease with up to 22,000 deaths a year, and Wolbachia mosquitoes stay put once released. A Brazilian biologist expects the virus to find a way around it anyway.