Optimizing influenza vaccination: timely protection of those most at risk

Abstract

Background: There are several high-risk groups in whom influenza-related mortality and complication rates are elevated compared with healthy individuals. Consequently, many countries follow the World Health Organization recommendations and have implemented programmes to ensure the most vulnerable groups are protected. Methods and materials: We searched published literature to summarise the data on influenza epidemiology, vaccine immunogenicity, efficacy, effectiveness and safety in high-risk groups. In addition, we looked at optimization of influenza vaccination through timing of administration and the impact of pre-existing immunity on vaccine response. Results: Evidence shows that influenza vaccine effectiveness in high-risk groups is approaching comparability with that seen in healthy individuals. Pregnant women, children aged 6 months–5 years and adults ≥65 years are perhaps the most well-known high-risk groups that can benefit from influenza vaccination. There are effectiveness and safety data in other groups to support vaccination against influenza, including those with: chronic respiratory disease, chronic cardiac disease, obesity, diabetes, chronic kidney disease, chronic liver disease, chronic neurological disease and compromised immune systems. Vaccination against influenza is required annually, this presents some challenges. First, the timing of vaccine administration can be problematic due to waning vaccine effectiveness during the influenza season and variations in viral transmission patterns. Early vaccination may mean that individuals are no longer optimally protected at peak transmission whereas vaccination after viruses start to circulate may result in large numbers of high-risk individuals being left unprotected. The optimal time to immunise likely varies depending on geographical location, it is therefore possible that recommendations on when to vaccinate should be individualized to countries/regions rather than provided globally. The second challenge is that the impact of exposure to influenza vaccine year on year is not well-understood. There is some evidence that repeated influenza vaccination each year may interfere with vaccine efficacy. Conclusion: Influenza vaccination can lower the risk of serious influenza-related complications and death in high-risk groups. More research is needed to overcome the challenges associated with optimising timing of influenza vaccination and understanding the impact of repeated vaccination on vaccine effectiveness. This review highlights the necessity to develop improved influenza vaccination strategies.