(223) Incidence of RSV Lower Respiratory Tract Infections Among Infants Considering Effects of Palivizumab Immunoprophylaxis

Saturday, August 27, 2022

8:00 AM – 6:00 PM CEST

Location: Hall C

Publication Number: 897

Presenting Author(s)

Almut Winterstein, PhD, FISPE
– Distinguished Professor, University of Florida, Gainesville, Florida, United States

Co-Author(s)

Phuong Tran, MPH
– Graduate Assistant, University of Florida College of Pharmacy, Gainesville, Florida, United States
Sabina O. Nduaguba
– Dr, University of Florida College of Pharmacy, Morgantown, West Virginia, United States
Renata Shih
– University of Florida, United States

Background: Respiratory syncytial virus (RSV) is the most common cause of lower respiratory tract infections (LRTIs) in infants. Recent incidence data do not exist for high-risk groups and for mild to moderate RSV disease. Such estimates are complicated by broad use of immunoprophylaxis, palivizumab, among high-risk groups.

Objectives: To estimate incidence of RSV-LRTIs among high-risk children in in- and outpatient settings, adjusting for palivizumab use.

Methods: Using IBM MarketScan® Commercial Claims Data 2011-2019, we calculated medically-attended RSV-LRTI incidence rates during the RSV core season (November-February). High-risk infants included those born preterm, with chronic lung disease (CLD), hemodynamically significant coronary heart disease (CHD), profoundly immunocompromised (IM), with neuromuscular disease (MD), cystic fibrosis (CF), and Down syndrome. We used American Academy of Pediatrics guidelines to define high-risk conditions. We estimated crude incidence rates of RSV-LRTIs ignoring palivizumab exposure (crude), and adjusted for periods of palivizumab exposure when the risk for infection was reduced(within 30 days of palivizumab administration). The adjustment divided the number of RSV LRTIs by efficacy estimates (preterm 78%, CLD 39%, CHD 45% for inpatient RSV-LRTI) or the average efficacy (50%) when condition- or outpatient setting-specific data were unavailable.

Results: Among infants ≤12 months old within prematurity strata (29; 29-31; 32-34; 35-36; ≥37 weeks GA), crude RSV-LRTI incidence rates decreased from 73-72-57-35-15 for inpatient and 243-352-286-247-168 for outpatient encounters per 10,000 children-month, respectively. Crude diagnosis-stratified incidence rates for inpatient (outpatient) encounters were 84 (332) for CLD, 101 (306) for CHD, 49 (163) for IM, 55 (264) for MD, 82 (267) for CF, and 157 (377) for Down. Immunoprophylaxis use is suggested for children with active CLD and IM in their second year of life; their incidence rates for CLD and IM were 108 (340) and 76 (149), respectively.
Adjustment for palivizumab exposure increased incidence rates by 100-123% for inpatient RSV-LRTI and 100-119% for outpatient RSV-LRTI.

Conclusions: Compared to background rates among healthy term infants (inpatient 15 and outpatient 168), high-risk groups had 3.3-10.5 (inpatient) and 1.0-2.0 fold (outpatient) higher risk for RSV-LRTI during their first year of life. Because of high palivizumab exposure, disease burden is underestimated if the protective effect of immunoprophylaxis is ignored.