Modelling the population effectiveness of the national seasonal influenza vaccination programme in Scotland: The impact of targeting all individuals aged 65 years and over.

Background: For the last 17 years, the UK has employed a routine influenza vaccination programme with the aim of reducing the spread of seasonal influenza. In mid-2000, the programme moved from a purely risk-based approach to a risk and age group-targeted approach with all those aged 65+ years being included. To date, there has been no assessment of the population effectiveness of this age-targeted policy in Scotland.

Objectives: Statistical modelling techniques were used to determine what impact the routine vaccination of those aged 65+ years has had on influenza-related morbidity and mortality in Scotland.

Methods: Two Poisson regression models were developed using weekly counts of all-cause mortality, cause-specific mortality and emergency hospitalisations for the period 1981-2012, one using week-in-year and the other using temperature to capture the seasonal variability in mortality/hospitalisations. These models were used to determine the number of excess deaths/hospitalisations associated with the introduction of the local risk and age-based vaccination programme in 2000.

Results: Routinely vaccinating those aged 65+ years is associated with a reduction in excess all-cause mortality, cardiovascular and COPD-related mortality and COPD-related hospitalisations. Our analysis suggests that using the week-in-year model, on average, 732 (95% CI 66-1398) deaths from all causes, 248 (95% CI 10-486) cardiovascular-related deaths, 123 (95% CI 28-218) COPD-related deaths and 425 (95% CI 258-592) COPD-related hospitalisations have been prevented each flu season among the those aged 65+. Similar results were found using the temperature model. There was no evidence to suggest that the change in policy was associated with reductions in influenza/pneumonia-related mortality or influenza/cardiovascular-related hospitalisations.

Conclusions: Routinely vaccinating those aged 65+ years appears to have reduced influenza-related morbidity and mortality in Scotland. With the childhood vaccination programme well underway, these data provide an importance benchmark which can be used to accurately assess the impact of this new seasonal influenza vaccination programme.