Prophylactic RSV Ab has been shown to be protective against severe RSV disease. We examined RSV disease incidence in children with underlying heart or lung disease relative to their Ab titer at the start of RSV season. Children ≤ 36 months with either underlying heart or lung disease were eligible for enrollment into the study. The preseason titer was determined from sera obtained at the beginning of the RSV season or the previous year's convalescent titer if the patient were enrolled in a RSV study the previous year. 427 patients were enrolled and sera were available from 350. Of these, 239 had underlying heart disease, 124 had chronic lung disease and 13 had both; 186 were male; 118 were less than 1 year, 120 were 1 - 2 years, and 112 were 2 - 3 years old. The RSV illness experience is summarized:Table The presence of Ab significantly modifies RSV illness experience and there are clear trends for reduced incidence of LRI, RSV hospitalization, and hospitalization in those with high antibody level that do not reach statistical significance. There was a much lower frequency of RSV hospitalization in this population compared to that observed in the previous trials of RSVIG, which may be due to differences in underlying disease severity between populations. (Funded by Lederle Praxis Biologicals)

Table 1
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