Rapid medical countermeasure (MCM) dispensing is an important intervention during a public health emergency. In the United States, MCM planning and exercising efforts have largely focused on dispensing therapeutics, with less emphasis on mass vaccination operations that would require additional specialized staff and infrastructure. Difficulties in distributing vaccines during the 2009 H1N1 influenza pandemic highlighted the need for enhanced planning and exercising of plans for conducting mass vaccination campaigns. In Taiwan, seasonal influenza mass vaccination campaigns are conducted annually, which both mitigate the effects of seasonal influenza and serve as functional exercises for mass vaccination operations during a pandemic. To identify lessons that can be applied to mass vaccination planning in the United States and elsewhere, we conducted an in-person observation and data review of Taiwan´s annual seasonal influenza mass vaccination efforts in October 2017. We offer findings and recommendations for enhancing preparedness for seasonal and pandemic influenza and other public health emergencies that would require mass vaccination.