Why do we not have a vaccine against congenital cytomegalovirus (CMV) infection?

Congenital cytomegalovirus (CMV) infection is a major cause of disability in newborns. In spite of knowledge that maternal immunity to CMV protects newborns against these disabilities, there is no licensed vaccine for CMV. The barriers to availability of a CMV vaccine include: (1) a lack of knowledge about the problem; (2) an incomplete understanding of the immune correlates of protection; and (3) uncertainty about what the proper target population is for vaccination. This review summarizes the current state of CMV vaccines and discusses the obstacles that must be overcome before the goal of a vaccine can be realized.