Table 4  Geometric mean titres (IU/l) (with 95% confidence intervals) at two and six months after vaccination (intention to treat analysis) Month Antigen (µg) No of subjects 2 6 5 25 10.0 (3.8 to 26.7) 11.9 (5.7 to 25.1) 10 25 26.9 (13.1 to 55.3) 28.6 (12.0 to 68.1) 20 25 58.5 (17.1 to 200.2) 57.5 (16.8 to 197.0) 40 25 79.7 (27.5 to 230.5) 61.8 (23.1 to 165.5) Total 100 33.5 (20.2 to 55.6) 33.2 (20.6 to 53.6) P value for trend 0.002 0.009