BACKGROUND: Influenza infection is an important trigger of asthma attacks. Influenza vaccination has the potential to reduce the incidence of influenza in people with asthma, but uptake remains persistently low, partially reflecting concerns about vaccine effectiveness (VE).
METHODS: We conducted a test-negative design case-control study to estimate the effectiveness of influenza vaccine in children and adults with asthma in Scotland over six influenza seasons (2010/11 to 2015/16). We used individual patient level data from 223 primary care practices which yielded 1,830,772 patient-years of data, which were linked with hospital and virological (n=5,910 swabs) data.
RESULTS: Vaccination was associated with an overall 55.0% (95% confidence interval (CI): 45.8-62.7) reduction in the risk of a laboratory-confirmed influenza infection in people with asthma over the six seasons. There was substantial variation in VE between seasons, influenza strains and age groups. The highest VE (76.1%; 95% CI: 55.6-87.1) was found in 2010/11 season where the A(H1N1) strain dominated and there was a good antigenic vaccine match. High protection was observed against A(H1N1) (e.g. 2010/11: 70.7%; 95%CI: 32.5-87.3) and B strains (e.g. 2010/11: 83.2%; 95%CI: 44.3-94.9), but there was lower protection for the A(H3N2) strain (e.g. 2014/15: 26.4%; 95%CI: -12.0-51.6). The highest VE against all viral strains was observed in adults aged 18-54 years (57.0%; 95%CI: 42.3-68.0).
CONCLUSION: Influenza vaccination gave meaningful protection against laboratory-confirmed influenza in people asthma across all six seasons. Strategies to boost influenza vaccine uptake has the potential to substantially reduce influenza triggered asthma attacks.
Bibliographical noteFinancial support. The work was funded by the Chief Scientist Office of the Scottish Government under the grant (AUKCAR/14/03) and the NIHR–Health Technology Assessment (HTA) Programme (13/34/14) for the Seasonal Influenza Vaccination Effectiveness II (SIVE II) study. As principal investigator, C. R. S. received a grant for the SIVE-II project from the NIHR HTA. This work was carried out with the support of the Asthma UK Centre for Applied Research (AUK-AC-2012-01), the Farr Institute (MR/M501633/2), Health Data Research UK (an initiative funded by UK Research and Innovation, Department of Health and Social Care England and the devolved administrations and leading medical research charities), the European Union’s Horizon 2020 research and innovation programme (under grant agreement No 634446) and European Centre for Disease Prevention and Control (Influenza-Monitoring Vaccine Effectiveness).
Acknowledgments. The authors thank and acknowledge all colleagues at the Asthma UK Centre for Applied Research for their support in this study.
Disclaimer. The funding bodies had no role in the design of the study, review process, analysis, interpretation, or reporting of data. The views and opinions expressed herein are those of the authors and do not necessarily reflect those of the Health Technology Assessment Programme, National Institute for Health Research (NIHR), National Health Service, or the Department of Health.
Potential conflicts of interest. The authors: No reported conflicts of interest. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed.
- laboratory-confirmed influenza
- Laboratory-confirmed influenza