Improved immunization practices reduce childhood hepatitis B infection in Tonga

Area of Science:

• Public Health
• Infectious Disease Epidemiology
• Vaccinology

Background:

• Hepatitis B infection is hyper-endemic in Tonga, with 19% of pregnant women testing positive for hepatitis B surface antigen (HBsAg).
• Despite routine childhood immunization since 1989, HBsAg prevalence in pre-school children remained at 3.8% in 1998.
• Enhanced hepatitis B vaccine delivery, emphasizing the first dose within 24 hours of birth, was implemented to curb transmission.

Purpose of the Study:

• To evaluate the impact of improved hepatitis B immunization practices on HBsAg prevalence in pre-school children.
• To assess Tonga's progress toward the elimination of hepatitis B infection in children.

Main Methods:

• A cross-sectional study was conducted involving children aged 6-59 months admitted to Vaiola Hospital.
• Hepatitis B surface antigen (HBsAg) was tested using rapid serological tests on 375 children.
• Immunization status was verified through cards and public health nurse records; socio-economic and other relevant data were collected via maternal interviews.

Main Results:

• HBsAg prevalence in the study group was 0.8%, achieving the elimination target of <1%.
• Hepatitis B vaccine (Hep B 1) first-dose coverage was high at 99.1%, with 91.9% administered within 24 hours of birth.
• Third-dose coverage reached 97.6%, and 84.7% of children completed the full immunization schedule by six months.

Conclusions:

• Strengthened hepatitis B vaccine delivery strategies have effectively reduced childhood hepatitis B transmission in Tonga.
• Tonga has likely achieved the hepatitis B elimination target of <1% HBsAg prevalence in children.
• Convenience testing is a cost-effective and reproducible method for monitoring immunization program effectiveness in settings with good healthcare access.