Active pre-exposure immunisation against hepatitis B virus: immunogenicity of hepatitis B vaccine in healthy Thai adults and children.

The immunogenicity of plasma derived hepatitis B vaccine (Hevac B) was studied for active pre-exposure immunisation in 176 healthy volunteer adults and 162 randomised children who had no hepatitis B virus markers. All subjects received three injections of 5 micrograms of hepatitis B vaccine intramuscularly at one month intervals. Seroconversion at 2 months after the third dose of vaccine was 96.30 percent in the children and 92.00 percent in the adults with mean anti-HBs titres of 800 mlU/ml and 353 mlU/ml respectively. The difference of anti-HBs levels between these two groups was statistically significant (p less than 0.05). Female adults had exhibited higher immune response to HB vaccine than male adults but there was no seroconversion difference between boys and girls. There were no serious local or systemic side effects of hepatitis B vaccination. It was concluded that active immunisation with plasma derived hepatitis B vaccine in non-immune children and adults is highly effective without any serious side effects or complications. The prevention of horizontal transmission of hepatitis B virus should be done by vaccination in children since they have a much better immune response to hepatitis B vaccine than adults.