Influenza-like illnesses are often found among staff members. The influenza immunization program just covered 30% of the total number of workers. This research was therefore carried out to observe the effectiveness of immunizing BP Indonesia - West Java workers against the symptoms of influenza-like illnesses. This research used a case-control design of 1:1. The number of random samples per group was 88 people. Influenza-like illnesses were influenced by vaccinations (OR=4.83), workers' locations (OR=3.94), exercise activities (OR=3.86), smoking (OR=2.86) and Body Mass Index (OR=0.44). The average length of illness for workers who were immunized was 3 (3-5) days, while those who were not immunized experienced an average length of 4 (2-7) days. This difference was significant, with a p value of 0.008. The effectiveness of the influenza vaccination against influenza-like illness symptoms was 69.4%. This influenza vaccination program was the main determinant factor in reducing the incidence of influenza-like illnesses, with an effectiveness rate of 69.4%. Copyright 2010, Society of Petroleum Engineers.