Abstract: 

Asthma is one of the most common chronic diseases of childhood, causing significant morbidity and mortality. Worldwide, the prevalence of asthma has been increasing for the past three decades. Respiratory syncytical virus (RSV) infection is the most common infection in infancy. More than 70% of infants are infected with RSV during their first year of life, and all infants are infected at least once by two years of age. It has long been known that severe RSV infection such as RSV induced bronchiolitis is associated with an increased risk of childhood asthma. However the mechanism behind RSV infection and asthma inception is unclear. Using infant age at winter RSV viral peak season as a marker, we reported that infants who were four months old at the winter RSV viral peak had the highest risk of RSV bronchiolitis, as well as the highest risk of developing asthmaby age six years, indicating that infant RSV infection is in the causal pathway of the development of asthma. To further demonstrate the causal relationship between infant RSV infection and asthma, we studied the only available medication that can prevent severe RSV infection, RSV immunoprophylaxis. We demonstrated that RSV immunoprophylaxis is effective in reducing RSV induced bronchiolitis hospitalization, as well as any healthcare visits (including outpatient visit, emergency department visit, and hospitalization) among infants who are at high risk for RSV infection. Our next step is to study whether RSV immunoprophylaxis is also effective in reducing the risk of asthma inception, thus potentially identifying an effective strategy of preventing asthma in susceptible children.