Haemophilus influenzae type B vaccination and risk of childhood leukaemia in a vaccine trial in Finland

Incidence of childhood leukaemia was studied among subjects of a trial comparing administration of several doses of a conjugate vaccine against Haemophilus influenzae type b (Hib) starting at an early age (three months) with a single dose given at the age of two years. Among 114 000 subjects, a total of 77 cases of childhood leukaemia were detected. The incidence of childhood leukaemia was lower in the early vaccination arm (relative risk 0.72, 95% confidence interval 0.46–1.13) than late vaccination arm, but the difference did not reach statistical significance. Our results suggest that early immunization against Hib may reduce the incidence of childhood leukaemia, but confirmatory studies are needed. © 2000 Cancer Research Campaign