Factors associated with uptake of influenza vaccine in people aged 50 to 64 years in Hong Kong: a case–control study

BACKGROUND In Hong Kong, people aged 50-64 years were added as a recommended priority group (recommended group) for influenza vaccination by the Department of Health (DH) starting from 2011/12 onwards. The coverage rate of influenza vaccination for this age group was suboptimal at 8.5 % in 2012/13. This study investigates the factors associated with the uptake of influenza vaccination among adults in Hong Kong aged 50-64 years. METHODS A case-control study was conducted in communities by street intercept interviews from 17 July to 15 August 2013. Cases were adults aged 50-64 years who had received the influenza vaccine in 2011/12 or 2012/13, while controls were the same as the cases, except they had not received the influenza vaccine in 2011/12 or 2012/13. Multiple logistic regression analysis was performed on the data to explore the associations between vaccination status and the variables. RESULTS Six hundred and four respondents in total were interviewed and included in the analysis. There were 193 cases (vaccinated) and 411 controls (non-vaccinated), with a case-to-control ratio of 1:2.1. The following were strongly associated with vaccination compared to other factors: 'eligible for free government vaccine' (OR6.38, 95 % CI, 3.43-11.87, p < 0.001); 'willing to receive flu vaccination for free' (OR4.84, 95 % CI, 2.13-11.03, p < 0.001); 'perceived having severe or moderate symptoms when contracting flu' (OR2.90, 95 % CI, 1.21-6.97, p = 0.02), and 'convenient to reach a vaccination location' (OR2.87, 95 % CI, 1.06-7.74, p = 0.04). The majority of the cases (80.8 %) and controls (93.9 %) were not aware that they belonged to a recommended group for influenza vaccination and most (>80 %) were willing to be vaccinated if it was free. CONCLUSIONS Factors related to free and convenient vaccination, the perception of the severity of symptoms when contracting influenza had a comparatively strong association with influenza vaccination uptake amongst 50-64 year olds, compared to other factors.