Health benefit for the child and promotion of the common good were the two most important reasons for participation in the FinIP vaccine trial.

Background And Aims: The Finnish Invasive Pneumococcal disease (FinIP) vaccine trial was a nationwide cluster-randomised double-blind trial designed to demonstrate the effectiveness of pneumococcal conjugate vaccine in vaccinated children and indirect effects in unvaccinated populations. Together with the parallel carriage/AOM trial, over 47,000 children were enrolled, 52% of the initial target. We conducted a questionnaire study to find out which factors affected parents' decision on their child's study participation.

Methods: A questionnaire designed to evaluate parents' attitudes to vaccine trial participation in general and the FinIP trial in particular was mailed after the trial enrolment period had ended to parents of randomly selected children: 1484 who participated in the trial and 1485 who did not participate.

Results: Altogether 1438 parents (48%) responded to the questionnaire. The response rate was higher among FinIP participants (65%, 965/1484) than among FinIP non-participants (32%, 473/1485). The two most important reasons for giving consent to the FinIP trial were the potential benefit of immunisation against pneumococcal diseases (75% of consenters) and the promotion of the common good and public health (11%). The reasons reported as most important for declining consent were suspicions of vaccine safety (36%) and the double-blind trial design (12%). Up to 65% of the non-consenters declared that drug and vaccine trials should not be conducted in children at all.

Conclusions: The expected health benefit for the child was by far the most important reason for consenting to the vaccine trial. Safety concern was the main reason for decline. Importance and necessity of clinical drug and vaccine trials among children and the rationale of the blinded studies should be thoroughly explained to the public. This may increase participation in future vaccine trials.