Zika virus is endemic in parts of Africa. Probably most people there, including girls, are infected with it in childhood. This will trigger a normal immune response, including the production of memory T and B cells. What that means is that if a pregnant woman there gets infected with it the memory cells will get activated, taking care of the virus before it has a chance to damage her foetus.

It is different in the Western Hemisphere - the virus arrived there in 2014. That means that pregnant women there have no immunity to it.

The evidence for a causal link between infection of a non-immune pregnant woman and damage to her foetus is fairly convincing see, for example, MMS: Error

This information from WHO discusses these issues WHO | Zika virus and complications: Questions and answers.

If I was a non-immune adult woman resident in a country where Zika virus has recently arrived I would certainly want access to a good vaccine against it before considering becoming pregnant.