I already have to breathe in pollutants released into my neighbourhood by other people without my consent. I have to deal with the aggregated effects of bad economic decisions made by others. Getting infected with a malaria vaccine instead of actual malaria via a mosquito bite without my consent would be the most benign of this type of problem.

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.