<qa>  How many subjects are randomised in the first part of the trial?The trial is conducted in two parts. In the first part, 50 of the subjects are randomised with allocation weights 4:4:1:1 to IPV SSI, 13 IPV-Al SSI, 15 IPV-Al SSI or 110 IPV-Al SSI, respectively. In the second part, the corresponding allocation weights are 1:1:4:4 for the remaining 50 of the subjects. 