Purpose: This study was conducted to compare the incidence rate of influenza-like illnesses between an influenza-vaccinated group and a non-vaccinated group of adults. Methods: From July 1, 2015 to July 30, 2015, self-reporting questionnaires were given to 300 adults living in the Seoul and Gyeonggi-do, Korea. 265 survey questionnaires that had an earnest response were used for data analysis. The collected data were analyzed using the statistical software SPSS Win 18.0 version. Results: 52.1% of the participants were vaccinated. The incidence rate of influenza-like illnesses was 11.3%. Within the influenza-vaccinated group, 12.3% experienced an influenza-like illness. On the other hand, in the non-vaccinated group, 10.2% experienced an influenza-like illness. There was no statistically significant difference in the incidence of influenza-like illness depending on vaccination status. Conclusion: During the influenza season from Fall 2014 to Spring 2015, there was no significant difference on the prevalence of influenza-like illness between the study participants whether they were vaccinated or not. Thus, future studies should confirm and closely examine this fact, whether it was a matter of pandemic strain selection or whether there were differences in the effects of adult influenza vaccination as reported in previous studies.