SAN DIEGO, CA—The humanized monoclonal antibody palivizumab has up to 58% effectiveness for reducing hospitalizations for severe Respiratory Syncytial Virus (RSV)-associated acute lower respiratory tract infections (aLRTI), suggest findings from a multicenter study reported at IDWeek 2015.

“Using a test-negative case-control design with molecular detection of RSV, palivizumab effectiveness was 58% (95% CI: 43.1– 69%) against aLRTI requiring hospitalization but confounding likely lowered this point estimate,” reported coauthor Eric A. F. Simões, MD, MB, BS, DCH, Department of Epidemiology and Center for Global Health, Colorado School of Public Health, Aurora, Colorado, and coauthors.

RSV-associated aLRTI occurs among children with chronic lung disease of prematurity, congenital heart disease, and preterm birth ≤35 weeks gestational age (wGA), the researchers noted.

Using nasopharyngeal aspirate PCR test data for RSV and human metapneumovirus collected between 2002 and 2006 for 849 eligible children admitted with aLRTI at age <2 years, the authors compared the odds of palivizumab administration between RSV cases and controls (OR). Palivizumab percent-effectiveness (PE) was then calculated as (1-OR) x 100, Dr. Simões explained.

Analysis was restricted to admissions during the November–April U.S./Canadian RSV season, he noted.

“Palivizumab was used in 434 children,” Dr. Simões reported. “Palivizumab use was more common among those who were older, were more premature, had lower birth weight, had prior NICU admission,  and had  longer NICU admissions” (P<0.0001 for all comparisons). For children aged 29–35 wGA and <6 months, the PE was calculated as 74.1% (95% CI: 56.2–84.7).

RSV was confirmed in 403 of the admitted infants. The calculated PE point estimate for RSV was 43% and the PE point estimate was -4% against human metapneumovirus (95% CI: -55.4% to 30.1%) among RSV-negative children, Dr. Simões reported.