Transmission of Respiratory Syncytial Virus Among Children Under 5 Years in Households of Rural Communities, the Philippines.

Background: To develop a more effective vaccination strategy for reducing the impact of respiratory syncytial virus (RSV) infection, especially in young infants (<6 months old), it is necessary to understand the transmission dynamics of RSV.
Methods: We conducted a community-based prospective cohort study from 2014 to 2016 in Biliran Province, the Philippines, on children <5 years old. We collected nasopharyngeal swabs from symptomatic children with acute respiratory infection (ARI) during household visits and at health facilities. In households (n = 181) with RSV-positive ARI cases (RSV-ARI), we also identified ARI episodes among other children <5 years old in the same household. In addition, we determined the serial interval to estimate the basic reproduction number ( R ₀ ), the average number of secondary cases generated by a single primary case.
Results: In the 181 households analyzed, we found 212 RSV-ARI in 152 households with a single case and 29 households with multiple cases, which included 29 1st RSV-ARI and 31 2nd RSV-ARI. We also found possible index cases among children <5 years old in the same household for 29.0% (18 of 62) of young infants with RSV-ARI. The estimated mean serial interval was 3.2 days, and R ₀ was estimated to be 0.92-1.33 for RSV-A and 1.04-1.76 for RSV-B, which varied between different times (2014 and 2015) and places.
Conclusions: Young infants are likely to acquire RSV infection from older children in the same household. Therefore, vaccination targeting older children might protect infants from RSV infection.