Impact of non-pharmaceutical interventions targeted at the COVID-19 pandemic on influenza cases in the UK Armed Forces

IntroductionNon-pharmaceutical interventions (NPIs) such as lockdown, social distancing and use of face coverings was adopted by the United Kingdom (UK) Armed Forces (AF) during the COVID-19 pandemic. This study assessed the impact of the use of NPIs on influenza activity in the UK AF. MethodsA longitudinal study design was adopted, and secondary data was analysed retrospectively. Clinical Read codes for influenza-like illness (ILI) was used to generate data for flu seasons before and during the COVID-19 pandemic (September 2017 to April 2021). ResultsBefore the COVID-19 pandemic, the rate of reporting ILI was [~] 4% across all flu seasons. The count of ILI was 2.9%, 2.2% and 3.1% during 2017-18, 2018-19 and 2019-20 flu seasons respectively. During the COVID-19 pandemic, both the rate of reporting ILI (0.6%) and the count of ILI (0.5%) were significantly smaller (p < .001). The rate of reporting ILI was positively correlated with the count of ILI (r (2) = .97, p = .014). Influenza vaccination rate increased by 1.3% during the COVID-19 pandemic. vaccination rate was negatively correlated with the rate of reporting ILI (r (2) = -.52, p = 0.24) and the count of ILI (r (2) = -.61, p = 0.19). However, this correlation was not significant. The use of NPIs was negatively correlated with the rate of reporting ILI (r (2) = -.99, p = < .001) and the count of ILI (r (2) = -.95, p = 0.026). The overall multiple regression performed was statistically significant (R2 = 0.94, F (1, 2) = 33.628, p = 0.028). The rate of reporting ILI significantly predicted the count of ILI ({beta} = 0.609, p = 0.028) while vaccination rate did not significantly predict the count of ILI ({beta} = -0.136, p = 0.677). ConclusionsInfluenza activity in the UK AF was significantly reduced during the COVID-19 pandemic. The use of NPIs and the rate of reporting ILI significantly reduced the count of ILI. Being vaccinated for influenza did not significantly reduce the count of ILI.