Hepatitis B vaccines, given to newborns around Taiwan since 1984, are now questioned for their effectiveness. Thirty-nine children living in a village of Taipei County were recently found to be free of antibodies to the disease, despite having been vaccinated at birth.

Mr. Huang's 14-year old son received three Hepatitis B vaccines when he was born and a fourth vaccine six years ago.

However, a recent physical exam revealed that the boy has no Hepatitis B antibodies.

Hepatitis B vaccines have been administered to all newborns in Taiwan since 1984, but 39 of Taiping Village's 67 children between the ages of seven and fifteen don't have any Hepatitis B antibodies.

According to doctors, antibodies sometimes disappear after a vaccine is administered, but the body remains protected against viruses as long as immunological memory remains.

Experts say that residential environment would not make antibodies disappear,

and that both domestic and foreign research show that Hepatitis B antibodies start decreasing in number around ten years after vaccination.

Therefore, periodic health checkups and blood tests can be used to determine whether another vaccine is required.