In Finland, respiratory syncytial virus (RSV) causes larger epidemics every second winter. The curve represents laboratory-proven cases of RSV infection in children aged 0–4 years during the smaller epidemic of spring 2015 and the larger epidemic the following season in 2016. The data are available in the public Infectious Disease Registry at the National Institute for Health and Welfare in Finland. The peak number of cases in March 2015 was 267 cases compared with 1192 cases in February 2016. The screening samples from the mothers were obtained at the end of the mild 2015 RSV season and the figure shows when the children of these mothers were born during the following severe 2016 RSV season.