The effectiveness of the infant hepatitis B immunisation program in Fiji, Kiribati, Tonga and Vanuatu.

The aims of this project were: (1) to determine the extent to which infant hepatitis B immunisation is preventing chronic hepatitis B infection in children living in a sample of Pacific Island countries; and (2) to identify factors associated with the successful prevention of hepatitis B infection in these populations. A regional hepatitis B immunisation project which supplied hepatitis B vaccine to 10 Pacific Island countries began in 1995. Seroepidemiological surveys were conducted in Fiji, Kiribati, Tonga and Vanuatu in early 1998. These included immunised pre-school children and their biological mothers, and a historical control group of unimmunised students. Prevalence rates for hepatitis B surface antigen (HBsAg) in the populations of students, mothers and their pre-school children were respectively: Fiji: 6.9, 6.6, 0.7%; Kiribati: 27.4, 15.1, 3.8%; Tonga: 11.1, 18.6, 3.8%; Vanuatu: 16.3, 12.3, 3.0%; and for all four countries: 13.2, 12.5, 2.6%. Compared to the historical control group of students, the pre-school population had a much lower probability of HBsAg positivity (relative risk [RR]=0.19 [95%CI: 0.12-0.31]). Statistically significant differences in risk were apparent for all the countries: Fiji: RR=0.10; Kiribati: RR=0.14; Tonga: RR=0.34; Vanuatu: RR=0.19. This is equivalent to an overall program effectiveness of 81% (95%CI: 69-88%) in reducing chronic carriage. Also, the overall protective effectiveness against vertical hepatitis B transmission resulting in HBsAg positivity among children exposed to HBeAg positive and negative carrier mothers, was estimated to be 70%. By age 6 months, when all children should have had three vaccine doses, completed immunisation rates ranged from 22 (Fiji) to 84% (Vanuatu). Coverage of the first dose being given within 2 days of birth varied from 43% in Kiribati to 92% in Tonga. In conclusion hepatitis B immunisation of infants in these four countries is having a substantial beneficial effect in preventing chronic hepatitis B infection. Nevertheless, there is significant scope for further improving the timeliness of immunisation.