The question is interesting. I used to work in a community pharmacy, and we went from village to village, sometimes on horseback or by landrover, educating families on cleanliness and building immunity. There was no Zika in Lesotho at the time, but there was a high incidence of PEM in children from 3 months to about 5 years and we encouraged families to practice good hygiene to build immunity. So, I am not sure I understand why those "factors" in your question would limit building immunity only to "causes like the Zika virus." What about the bacteria linked to microcephaly?
Victoria Sethunya Good points. I would consider bacterial sources in the same broad category as viruses, as opposed to factors one cannot develop immunity to, such as genetic factors.