Seasonal influenza vaccine use in low and middle income countries in the tropics and subtropics: a systematic review

This systematic review aims to assess the scientific evidence on seasonal influenza vaccine use and effectiveness in Low and Middle Income Countries, in particular those situated in the tropical regions. Overall, the bulk of scientific evidence on vaccine use and effectiveness in the tropics comes from Latin America and the Caribbean and Asia; Africa remains underrepresented. Latin America and the Caribbean countries have led the seasonal influenza vaccination amongst Low and Middle Income Countries in the tropics and subtropics. Most of Asia and Africa are yet to introduce seasonal influenza vaccine into their national policy and program. Majority (61%) of the countries for which information was available prioritized pregnant women for vaccination against seasonal influenza. Vaccination campaigns in tropical countries (in both hemispheres) where increased influenza activity frequently coincides with the rainy season should be timed with the availability of the southern hemisphere vaccine formulation. The timing of vaccination and the choice of formulation in the tropics should be guided by laboratory-confirmed influenza seasonality data facilitated by a strengthened surveillance capacity. Surveillance systems in tropical countries need to be strengthened to better understand seasonality, epidemiology and virological aspects of influenza in the tropics so as to optimize the WHO recommendation for the seasonal influenza vaccine composition for the tropics.