Drawing blood from young children: lessons learned from a trial in Ghana.

This paper reflects on lessons learned from a trial in Ghana assessing the impact of vitamin A supplementation on children's immune responses to tetanus and polio vaccines. There were more losses to follow-up than was anticipated at visits during which blood was drawn, owing to concerns or misconceptions about blood draw. The trial initially planned to recruit 960 children but had to recruit more because the proportion of infants lost to follow-up was greater than the anticipated 15%, resulting in a longer recruitment period. Of 1085 infants who were randomised into the trial, 767 (71%) completed follow-up at 6 months of age. It was notable that at the first (6 weeks) and fourth (6 months) visits at which blood was drawn, losses to follow-up were greater than at the second (10 weeks) and third (14 weeks) visits during which blood was not drawn. Losses to follow-up pose a threat to the validity of trials as there is a chance that those lost to follow-up may differ from those who remain in the trial. Monitoring losses to follow-up as they emerged and allowing mothers to witness the blood draw, as well as holding community meetings, helped to allay anxieties in the community.