Sleep regulates immune functions. In this sense, we asked whether shift workers (morning, afternoon or night) vaccinated against hepatitis A would have some humoral and cellular response impairment. Men (18 to 55 years) will be recruited through different forms of media (electronic, newspapers, radio and magazines). The shift workers sleep pattern will be recorded polysomnographically. Subsequently, the volunteers will be underwent vaccination against hepatitis A (2 doses) and after 30, 60 and 90 days, blood samples will be collected to assess the humoral response in the experimental groups. The hormones prolactin, growth hormone, cortisol, adrenaline and noradrenaline will also be evaluated. Indeed, stimulations in culture will be conducted to assess the cellular response profile against the vaccination through the production assessment of IL-4, IFN-γ, IL-2 and TNF-α.