Clinical evaluation of a yeast recombinant hepatitis B vaccine in healthy hospital staff in Singapore.

A yeast recombinant hepatitis B vaccine (subtype adw), derived from purification of HBsAg particles, expressed in the yeast Saccharomyces cerevisiae which contained the gene for HBsAg, was evaluated in 31 healthy adult hospital staff members in Singapore. Each subject received a 10 mcg dose of vaccine intramuscularly at 0, 1 and 6 months. One month after the first two injections of vaccine the seroconversion rate (defined as greater than or equal to 2.7 mIU/ml) was 90%. Two months after the third injection 100% of participants had anti-HBs levels higher than 2.7 mIU/ml and 97% had titers of anti-HBs greater than 10 mIU/ml. The geometric mean titer (GMT) of anti-HBs levels at 2, 3, 6, 8 and 12 months were 21.9, 38.6, 57.6, 1253.4 and 354.1 mIU/ml, respectively. All clinical complaints were mild and transient. They consisted of mild soreness at the injection site, transient fever and headache. There was no correlation between the presence of antibodies to S. cerevisiae with any allergic manifestations. The vaccine was safe and immunogenic for staff exposed to an infection risk and should now be widely used in the extension of hepatitis B immunization programs.