HBIG, it is 85 to 95 percent effective in preventing perinatal HBV infection (Szmuness et al., 1982). Immunocompromised individuals do not respond as well to the current vaccines. Only 50 to 60 percent of dialysis patients and an even lower proportion of oncology patients develop anti-HBs following complete immunization (Crosnier et al., 1981; Desmyter et al., 1983; Stevens et al., in press [a]). Moreover, efficacy of the current vaccine in these groups has not been clearly established.
Hepatitis B occasionally occurs despite administration of vaccine. Thus far, such cases have been limited to the initial immunization period (i.e., before protective antibody develops) and to nonresponders to the vaccine (less than 5 percent of those immunized). Long-term follow-up of vaccine recipients indicates that detectable, vaccine-induced anti-HBs persists for at least four to five years in 90 percent or more of vaccine responders (Stevens et al., in press [b]).
When HBV infection is prevented, the risk of chronic HBV infection also is prevented. Thus, effective immunization of those at risk eventually should produce the secondary benefit of reducing the pool of chronic HBsAg carriers, the primary source of HBV.
Hepatitis B vaccine currently is recommended in the United States only for high-risk groups. Although this approach seems reasonable for the moment (with limited supplies of a fairly expensive vaccine), it restricts the number of hepatitis B cases that can be prevented. The actual proportion of cases prevented is probably far less than 50 percent, because many people at high risk are not recognized by the physician (e.g., infants and close contacts of undetected HBsAg carriers) or do not identify themselves (e.g., some homosexual men and drug addicts).
The need for a new generation of hepatitis B vaccines is clear. The goals in developing these vaccines would be to enhance immune responsiveness (especially for immunocompromised populations), to make available an unlimited resource of antigenic material, to reduce the cost of immunization, and to reduce the fear of side effects.
Defining the target population is the first step in calculating the benefit 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 CDC Sentinel County Study results indicate that approximately 50 percent of illness from hepatitis B occurs in the high-risk target population and this is the portion considered vaccine preventable in this study (Alter, 1983; Francis et al., 1984). The estimates of VPI are shown in Table H.3.