Study population: 90 people with clinically proven asthma, who are not carrier of hepatitis A, B or C and have not been vaccinated against hepatitis A in the past. Also, these participants do not have any other immune-related pathology Main study parameters/endpoints: primary: Specific anti-HAV antibody titers after vaccination; secondary: Phagocytic capacity of neutrophils; NK-cell activity; Th1 and Th2 cytokine production profiles by PHA stimulated PMBCs.