Universal palivizumab prophylaxis for children with Down syndrome in Japan: analysis with interrupted time-series.

Down syndrome (DS) is an independent risk factor for severe respiratory syncytial virus (RSV) infection. Palivizumab - passive immunization for RSV - is the only pharmacological measure for preventing severe disease. In most countries, palivizumab is indicated in young children with congenital heart disease, premature birth, and chronic lung disease. In Japan, since 2013, children with DS, but without such "standard" risk factors, have been able to receive insurance-covered palivizumab prophylaxis, but its effectiveness of policy is unknown. From a nationwide database, we extracted data of children with DS who hospitalized for RSV-related lower respiratory infections (LRTIs), from April 2010 to January 2019. Using an interrupted time-series design, we analyzed data from before and after the introduction of the universal palivizumab prophylaxis program for DS children in Japan. As a result, we identified a total of 152 RSV-related LRTIs in 147 children hospitalized with DS. With time-series analysis, we did not observe a significant change in both level (-1.07, P = .11) and slope (0.26 per 12 months, P = .30), before and after 2013. In summary, the expansion of the palivizumab prophylaxis program to all children with DS in Japan was not associated with a reduction in RSV-related hospitalization in these children.