The same thing ordinary mosquitoes do already?
Right now you can consent to get a malaria vaccine, no covert parasite needed.
If the counter that it is for poorer populations, I'd still say you may want to ask them if they want to be injected with a genetically modified parasite. If one single person doesn't want to be in the area, you shouldn't do it. Would you support them dropping these in your neighborhood?
Oh, and this already happens with the attenuated polio vaccine. People can catch the vaccine from those who have been immunised, in a similar way to how they could catch the virus. Delivering the vaccine the same way the pathogen spreads also allows people to opt out by following the same techniques they would to avoid the actual disease. You can use mosquito nets, mosquito sprays, etc., to help avoid both malaria and the mosquito-delivered vaccine.