- Background After a case of hepatitis A in a food handling worker in a military base, the entire exposed population was vaccinated with immune serum globulin (ISG). We analyzed the potential effects of ISG on asthma attacks and respiratory infections. Methods The base population was observed for asthma exacerbation for the 3 months after the immunization and was compared with the population of the same base a year earlier. Rates were tested using χ 2 statistics. Results The vaccinated population had a highly significant decrease in the incidence of asthma attacks (rate ratio [RR] = 0.2, 95% confidence interval [CI] 0.09 to 0.45), sinusitis (RR = 0.34, 95% CI 0.2 to 0.58), and pneumonia (RR = 0.41, 95% CI 0.17 to 0.99). No significant difference was observed in the incidence rates of upper respiratory infections between the two groups. Conclusions A single administration of ISG significantly reduces the rate of asthma attacks and respiratory infections.