Table 2

Influenza vaccine effectiveness against hospitalisation for acute respiratory infection in people aged 65–100 years, Finland, August 2012–May 2020

Season Cohort size Unvaccinated Fully vaccinated Vaccine effectiveness a %
Cases Attack rateb Cases Attack rateb Estimate 95% CI
2012/13 802,597 13,822 2,439 6,717 2,799 −1 −5 to 2
2013/14 829,885 12,605 2,249 6,675 3,206 6 2 to 10
2014/15 950,866 16,594 2,627 8,818 4,674 4 1 to 7
2015/16 991,056 16,998 2,660 8,800 4,118 2 −1 to 5
2016/17 1,023,992 17,411 2,843 11,282 3,133 0 −3 to 3
2017/18 1,069,160 17,710 2,788 11,716 2,865 3 0 to 6
2018/19 1,125,151 14,584 2,150 9,457 2,057 −2 −6 to 1

CI: confidence interval.

a Vaccine effectiveness was defined as 1 minus the covariate-adjusted hazard ratio. The covariates were age, sex, 1-year vaccination history, nights hospitalised in the past 5 years and presence of underlying chronic conditions.

b The attack rate is presented as the cumulative risk at the end of the study period multiplied by 105.