Secular trends were considered in the evaluation of universal hepatitis B vaccination in Taiwan

The objective was to evaluate time-trend bias in the context of a series of studies reporting that a national hepatitis B virus vaccination program (launched in mid-1980s) substantially reduced childhood hepatocellular carcinoma (HCC) incidence.

We applied an age-period-cohort model to evaluate the relative importance of age, time-trend (period), and vaccination (cohort) effect, respectively, on the incidence and mortality rate of HCC in boys and girls in Taiwan from 1980 to 2009.

HCC incidence increased with age. The period effect analysis revealed that the incidence of HCC started to decrease in 1980s, leveled off in mid-1990s, and declined again in mid-2000s among boys. The period effect was flat among girls. Cohort effect analysis demonstrated that among boys, the incidence of HCC started to decrease by those born in 2000-2004, which was 15 years later than the first vaccinated cohort. Among girls, the incidence rate started to decline before the mass vaccination program was initiated. The analysis showed a decline in mortality for boys and girls born in 1980s.

Time trend may play a more important role than the universal vaccination program in interpretation of the observed early decreasing trend in HCC in children, especially among boys.