Introduction

The Finnish Vaccination Register, established 10 years later, records all vaccinations administered in the programme since 2009 [1]. The vaccines are selected by the Ministry of Social Affairs and Health in open tendering processes. Trivalent inactivated influenza vaccine was used until the end of season 2017/18 and thereafter replaced by a tetravalent inactivated influenza vaccine.

Assuming that influenza vaccination provides partial protection for the vaccinated, an appropriate measure of the protective direct effect under real-life conditions is influenza vaccine effectiveness (IVE) defined as the vaccine-attributable relative reduction in the hazard of influenza disease [2,3]. To guide public health measures as well as individual-level decision-making, IVE in elderly people is estimated regularly in Finland using a register-based cohort study design [4].

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