Regarding genetically modified mosquitos whose salivary glands secret an antibody which stops the microbe which causes malaria from being spread to humans during feeding.

One of the easiest and often most effective means of controlling the spread of malaria is to control the mosquitos that carry it to humans. Unfortunately, that has proven to be just as much of an evolutionary arms race as targeting malaria itself...

Recent efforts have focused on forms of control that don't impose a huge fitness burden on the mosquito population...

From the perspective of not harming the mosquitos, it all seemed to work. Females appeared to be completely unaffected by the inserted genes, and males had only slightly reduced lifespans, which came well after their peak period of fertility. From the mosquito's perspective, the antibody genes don't seem to do it significant harm, so won't cause any sort of selective pressure to get rid of them.