B Young

Hepatitis B virus (HBV) infection and disease is a major public health problem. Worldwide, it is estimated that about 300 million people are carriers of HBV, and more than 1 million deaths annually are attributed to serious sequelae of chronic HBV infection. Hong Kong is a high endemicity area of the infection. An epidemiological study in 1978 showed that about 10% of the population were carriers of HBsAg and 75% above the age of 50 had evidence of previous infection by the virus. However, recent studies revealed a declining trend of HBV prevalence. It is estimated that the HBV carrier rate is currently about 8%.

Since there is no established therapy for hepatitis B, prevention of the infection by immunization with hepatitis B vaccine is the most effective means to decrease the incidence of the infection. In Hong Kong, a pilot study of immunizing born to HBsAg-positive mothers with hepatitis B immunoglobulin (HBIG) and hepatitis B vaccine was started in 1983. The results revealed that the efficacy of hepatitis B vaccine was dependent on maternal HBeAg status and the long term immunogenicity was determined by the age at which vaccination was commenced. The dosage and schedule of the vaccine, and of HBIG appeared less important in the long term efficacy and immunogenicity. The effect of a booster dose of the vaccine was studied and the results showed that although there were anti-HBs responses, the antibody titres were not well sustained. Natural boostering of anti-HBs was also observed, regardless of anti-HBc seroconversion.

The effectiveness of reduced dose (2.5 μg) of hepatitis B vaccine (B-Hapac II) was compared with the 5 μg dose in low-risk neonates and pre-school children. The seroconversion rates were comparable in the 2.5 μg and 5 μg groups in both newborns and pre-school children; however, it was significantly lower in newborns receiving 2.5 μg if positive response was taken as a titre >10 IU/l. The older children achieved a high seroconversion rate and antibody titre when compared with the newborns, irrespective of the dosage.

In Hong Kong, since 1985, all babies born to carrier mothers received HBIG and hepatitis B vaccine at birth. From 1989, all newborns were vaccinated; and in 1992, this programme was extended to pre-school children.