Abstract
<h3>In Reply. —</h3> We congratulate Coles et al on the innovative use of discharge diagnosis data, and we agree with the conclusion that the polysaccharide<i>Haemophilus</i>vaccine provided protective efficacy in children aged 24 to 59 months. A randomized trial of the vaccine in Finland<sup>1</sup>as well as three postlicensure case-control studies<sup>2-4</sup>all demonstrated a protective effect of the vaccine. Only one study,<sup>5</sup>a small case-control study with wide confidence limits, suggested a lack of efficacy. Although surveillance data can provide important supporting evidence of efficacy, there are methodological difficulties in using surveillance data to estimate the efficacy of a vaccine, as can be seen in the data presented by Coles et al. Year-to-year variation during the period of 1980 to 1984, when no vaccine was available, was substantial for the two younger age groups, 0 to 23 and 24 to 59 months of age. In fact,
Published Version
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