There have been two promising phase II trials into a vaccine for CMV. One trial (Pass et al 2009) was undertaken in adolescent and young adult women with a particularly high risk of acquiring primary CMV infection (e.g. a substantial proportion had a toddler at home) . The study found that a glycoprotein B (gB) vaccine gave 50% protection against acquiring a primary CMV infection for those who had not been infected before. These suggest that a gB vaccine may be able to prevent congenital CMV transmission in women of childbearing age.
However one of the main complications in developing a vaccine is the fact that congenital CMV infection does not just occur when a woman catches CMV for the first time when pregnant. It can also occur if she has pre-existing immunity but then catches a new strain of the virus. A further phase II study on glycoprotein B vaccine was carried out on transplant patients (Griffiths et al. 2011). The results of this trial were significant because it increased protection against CMV infection in those who had never had a strain of CMV before (seronegative) and those who had previously caught a different strain of the virus (seropositive).