Influenza B virus infections account for a substantial proportion of cases of influenza annually, with a high morbidity and mortality burden, especially in children (aged 0–18 years). Influenza B virus, on average, accounts for 23% of the annual influenza cases globally, although it can account for up to 80% of infections in some seasons and geographical locations, 1 with an estimated 7·9 million lower respiratory tract infections and 1·4 million hospitalisations annually. The majority of this burden is on school-aged (aged 5–18 years) children and adolescents, with up to 52% of influenza-related paediatric deaths being attributed to influenza B virus. 1 Of the estimated US$3·5 billion in influenza-associated health-care costs in the US annually, 37% are attributed to influenza B virus infections (～1·3 billion on average). The theoretically plausible eradication of influenza B virus could remove this considerable clinical and economic burden.