Seasonal influenza vaccine policy, use and effectiveness in the tropics and subtropics – a systematic literature review

Aim: The evidence needed for tropical countries to take informed decisions on influenza vaccination is scarce. This paper reviews policy, availability, use and effectiveness of seasonal influenza vaccine in tropical and subtropical countries. Method: Global health databases were searched in three thematic areas – policy, availability and protective benefits in the context of human seasonal influenza vaccine in the tropics and subtropics. We excluded studies on monovalent pandemic influenza vaccine, vaccine safety, immunogenicity and uptake, and disease burden. Results: Seventy-four countries in the tropics and subtropics representing 60% of the world's population did not have a national vaccination policy against seasonal influenza. Thirty-eight countries used the northern hemisphere and 21 countries the Southern hemisphere formulation. Forty six countries targeted children and 57 targeted the elderly, though the age cut-offs varied. Influenza vaccine supply increased two-fold in recent years. However, coverage remained lower than 5 per 1,000 population. Vaccine protection against laboratory-confirmed influenza in the tropics ranged from 0 to 42% in the elderly, 20 to 77% in children and 50 to 59% in healthy adults. Vaccinating pregnant women against seasonal influenza prevented laboratory-confirmed influenza in both mothers (50%) and their infants less than 6 months (49 to 63%). Conclusion: Guidelines on vaccine composition, priority risk groups and vaccine availability varied widely. The evidence on vaccine protection was scarce. Countries in the tropics and subtropics need to strengthen and expand their evidence-base required for making informed decisions on influenza vaccine introduction and expansion, and how much benefit to expect. (aut. ref.)