As noted above, questions exist regarding the ability of attenuated live vaccines to protect high-risk individuals against CMV infection. Other options might be useful in ameliorating CMV-related illness occurring during the post-transplant period. Cheeseman et al. (1979) have demonstrated that prophylactic administration of interferon may prevent cytomegalovirus infection following renal transplantation. In an analogous situation, it has been demonstrated that the administration of antiviral compound can decrease post-transplant complications caused by herpes simplex infection. Thus, it is possible that antiviral drugs or interferon may offer sufficient temporary protection to the transplant recipient during the period of greatest risk.
Defining the target population is the first step in calculating the possible reduction in morbidity and mortality that could be produced by a vaccine candidate. This knowledge can be translated into an estimate for vaccine preventable illness (VPI). VPI is defined as the number of cases, complications, sequelae, and deaths that could be prevented by immunization of the entire target population with a hypothetical vaccine that is 100 percent effective.
The primary purpose of immunizing nonpregnant adolescent females would be to prevent disease associated with congenital and perinatal CMV infection, so only that portion of the total CMV disease burden is considered here. The vaccine also may protect recipients from CMV disease; however, to simplify the calculations of vaccine preventable illness, the potential reduction in disease burden in recipients of the vaccine is not considered. The degree to which this simplification underestimates the potential benefits of the vaccine is considered minor, but could be calculated using the estimates of disease burden provided in this report.
Because reactivation of maternal infection contracted prior to administration of the vaccine could result in congenital or perinatal infection, it is estimated that even if the entire target population were immunized, some congenital and perinatal infection and disease would continue to occur. In calculating the extent of vaccine preventable illness, it is assumed that 10 percent of symptomatic congenital and perinatal infections result from reactivation of virus. Thus, 90 percent of the symptomatic congenital and perinatal infections are assumed to be potentially vaccine preventable.