How can scientists know whether a genetically modified-mosquito product successfully prevents disease?

An important aspect of the phased testing pathway is assessing efficacy (the ability to produce the desired effect). Efficacy testing begins with measurement of entomological characteristics, such as whether the modification is stable, adversely affects the survival or mating competitiveness of the mosquitoes, and reduces either the mosquitoes’ ability to reproduce or carry the pathogen of interest. These characteristics can help predict the product’s future efficacy for preventing disease. However, the ability of the product to reduce the incidence or prevalence of infection or disease can only be assessed in subsequent large-scale field trials. These will be conducted similarly to other types of clinical trials, according to internationally agreed upon ethical standards as well as applicable national and local regulatory requirements. Pre-determined performance milestones will determine whether efficacy results justify continued testing at each phase.

For more information:

https://www.who.int/publications/i/item/9789240025233
http://www.ajtmh.org/content/journals/10.4269/ajtmh.18-0083
https://apps.who.int/iris/bitstream/handle/10665/259688/WHO-HTM-NTD-VEM-2017.03-eng.pdf