From this AFP story hosted at Google News, we find this further explanation.
A new study shows real promise for turning the reviled insects into heroes by genetically modifying them to make them "flying vaccinators", according to scientists at Jichi Medical University north of Tokyo.
The researchers have already genetically modified a mosquito species so that its saliva contains a protein that acts as a vaccine against leishmaniasis, a sandfly-borne disease that triggers terrible skin sores and can be fatal.
The team confirmed that mice bitten by the transgenic mosquito developed an antibody to the disease, meaning they had built up immunity, said Shigeto Yoshida, the associate professor who has led the research.
Similarly the mosquitoes could be used to help combat malaria, perhaps a decade from now, said the malaria expert.
"What's good is that they don't charge you for vaccinations," Yoshida told AFP by telephone on Wednesday.
"You would be vaccinated without even noticing. You wouldn't need any drug and you wouldn't need to show up at a designated place for mass vaccinations."
Repeat bites would only strengthen the immunity, he said.