RSV - a substantial slice of the airway disease burden and the way to a vaccine

Background: The impact of an active RSV vaccine in the future will depend on the true fraction of airway diseases attributable to RSV as the causal pathogen, since many pathogens contribute to the airway disease burden at the same time. This attributable slice of the airway disease burden can vary between populations, regions and seasons, and by the incidence of co-infections. Furthermore, potential future vaccine effectiveness will depend on several characteristics such as prevention of vaccine escape mutants and earliest possible time of vaccination. Aims and Methods: To analyse the disease burden attributable to RSV and review recently published, high-quality epidemiological data from all parts of the world. The development of an active RSV vaccine is illustrated and hurdles in delivery are described. Results: RSV is estimated to be responsible for up to 22% of severe lower respiratory tract infections in children under 5 years of age. First lifetime RSV infections occur at a very early age, mainly in infants and toddlers, in a seasonal pattern, and lead to bacterial co-infections in about one-third of patients. The development of an active RSV vaccine faces several hurdles such as incomplete natural immunity, high variability of RS viruses, selection of the best antigens, choosing the proper vaccine technology platform, and lack of an immune correlate of protection. Added to this is the long way a clinical development programme has to go before it is possible from a regulatory point of view to test a vaccine candidate in a considerable number of RSV-naive children. Conclusion: An active RSV vaccine is urgently needed, but, given experience in the 1960s with the formalin-inactivated vaccines, and the long and complicated process involved in development, considerable support and flexibility by regulatory bodies and substantial funds are needed. The slice of up to 22% of the ARI disease burden in the first 5 years of life, which is potentially preventable by an active vaccine, is substantial, and the endeavour worthwhile.