Evaluating the effectiveness of the influenza vaccine during respiratory outbreaks in Singapore's long term care facilities, 2017.

•Influenza vaccine effectiveness (VE) was estimated using respiratory outbreak data.•VE was estimated to reach as high as 67.9% against influenza A(H3N2).•In contrast, estimated VE against influenza A(H1N1)pdm09 was only 35.4%.•Higher effectiveness was also seen in individuals who were recently vaccinated.•Our study provides novel data on influenza vaccine effectiveness in the tropics.