Improving influenza vaccination rates in the workplace: a randomized trial

Background: To minimize absenteeism resulting from influenza, employers frequently offer on-site influenza vaccination to employees. Yet the level of uptake of vaccine is low among working adults. This study was designed to increase workplace influenza vaccination rates by offering both a choice of intranasal (LAIV) and injectable (TIV) influenza vaccines to eligible employees, and an incentive for being vaccinated, and by increasing awareness of the vaccine clinic.

Design: This study used a stratified randomized cluster trial.

Setting/participants: A total of 12,222 employees in 53 U.S. companies with previous influenza vaccine clinics were examined.

Interventions: Control sites advertised and offered vaccine clinics as previously done. Choice sites offered LAIV or TIV and maintained their previous advertising level but promoted the choice of vaccines. Choice Plus sites increased advertising and promoted and offered a choice of vaccines and a nominal incentive.

Main outcome measures: These included vaccination rates among eligible employees. Hierarchic linear modeling (HLM) was used to determine factors associated with vaccination.

Results: The overall vaccination rate increased from 39% in 2007-2008 to 46% in 2008-2009 (p<0.001). The difference in vaccination rates for LAIV was 6.5% for Choice versus Control and 9.9% for Choice Plus versus Control (both p<0.001). Rates of TIV increased by 15.9 percentage points in the Choice Plus arm versus Control for workers aged > or =50 years (p=0.024). Rates of TIV did not change in workers aged 18-49 years in either intervention arm or in workers aged > or =50 years in the Choice arm. In HLM analyses, factors significantly associated with increased vaccination were older age, female gender, previous company vaccination rate, and the Choice Plus intervention.

Conclusions: An incentive for vaccination, an intensified advertising campaign, and offering a choice of influenza vaccines improved vaccination rates in the workplace.