The impact of repeated vaccination using 10-year vaccination history on protection against influenza in older adults: a test-negative design study across the 2010/11 to 2015/16 influenza seasons in Ontario, Canada Kwong, Jeffrey C and Chung, Hannah and Jung, James KH and Buchan, Sarah A and Campigotto, Aaron and Campitelli, Michael A and Crowcroft, Natasha S and Gubbay, Jonathan B and Karnauchow, Timothy and Katz, Kevin and McGeer, Allison J and McNally, J Dayre and Richardson, David C and Richardson, Susan E and Rosella, Laura C and Schwartz, Kevin L and Simor, Andrew and Smieja, Marek and Zahariadis, George and on behalf of the Canadian Immunization Research Network (CIRN) investigators, Eurosurveillance, 25, 1900245 (2020), https://doi.org/10.2807/1560-7917.ES.2020.25.1.1900245