by wasoxygen

CMV is so good at evading the immune system that it can “superinfect”, where an individual who is already latently infected develops a second primary infection. This is quite unusual for a virus. In the case of CMV, superinfection depends on its ability to evade the response of CD8+ T-cells (18). The possibility of superinfection is a discouraging sign for vaccine development, since it indicates that the normal immune response is inadequate to prevent CMV infection.

Interestingly, it’s been hypothesized that romantic kissing evolved as a method to reduce congenital CMV by ensuring that the mother was infected prior to pregnancy, rather than during pregnancy (21). I don’t know if this has any evidence, but it seems plausible. Overall I would still recommend trying to avoid CMV exposure prior to pregancy.