A fourth dose of DTPa-IPV vaccine given to 4-6 year old children in Italy and Sweden following primary vaccination at 3, 5 and 11-12 months of age

Healthy 4–6 y old children from Italy and Sweden immunized with DTPa and inactivated or oral polio vaccines at 3, 5 and 11–12 months of age, received 1 dose of combined DTPa-IPV (n=211) or DTPa+IPV as separate doses (n=205) in a randomized trial. The pre-booster seroprotection rates were similar in each group and were above 60% against all antigens except diphtheria (31.3% and 37.0%) and PT (21.5% and 25.9%) in the DTPa-IPV and DTPa+IPV groups, respectively. At least 99.5% of subjects had seroprotective antibody levels against diphtheria, tetanus and polioviruses and ≥96% showed a vaccine response to each pertussis antigen after vaccination. Post-booster antibody levels increased at least 51-fold for anti-diphtheria and anti-tetanus, at least 18-fold for anti-pertussis antibodies and at least 32-fold for antibodies against all 3 poliovirus types, compared to prior levels. DTPa-IPV was comparable to DTPa+IPV in terms of seroprotection rates and mean antibody levels against each vaccine antigen. Similar rea...