Abstract 998 Poster Session IV, Tuesday, 5/4 (poster 85)

Healthy infants were enrolled soon after birth and were followed for up to three RSV seasons. Data on their first RSV season is presented. Blood specimens and nasal secretions were collected prior to and after the RSV season. Weekly telephone interviews captured acute respiratory illness (ARI) data. Medically attended ARIs were cultured for RSV. From 1992 to 1995, 86 of the 90 enrolled infants were exposed to their first RSV season. Primary RSV infection occurred in 50 (58.8%) of 86 infants; twelve of the infections were culture positive for RSV. The date of onset and the serum neutralizing antibody (NtAb) titer at onset of the RSV infection were not known in most of the cases. Medically attended lower respiratory tract illness (MD-LRTI) was significantly associated with RSV infection, RSV culture positive illness, and family history of asthma (p < .024). Infants with preseason NtAb titer to RSV/A of 5.5 log2 or greater were less likely to become infected with RSV (p = .005). Noninfected infants had higher preseason geometric mean NtAb titer to RSV/A compared to RSV infected infants (6.5 log2 vs 5.1 log2; p = .016). Multivariate analysis revealed that RSV infection was the only factor associated with the level of postseason NtAb titer (p < .004). Neither age of infant at the start of the RSV season or preseason NtAb titer modified the postseason NtAb titer. However, we did not determine if age or level of NtAb at onset of RSV infection modified the postseason NtAb titer. An understanding of the immune responses induced by RSV infection and immune correlates will be useful in evaluating RSV candidate vaccines.

Funded by the Acute Viral Respiratory Disease Unit, contract NO1-AI-15103 and SmithKline Beecham Pharmaceuticals