Inclusion Criteria:  Indicator case: Babies under 5 months of age were born in Mackay Children's Hospital and had no acute respiratory infection-like symptoms that required medical intervention when they agreed to participate in the trial. Family members: family members living with the Indicator case, including 2-5 years old siblings, parents and grandparents over 65 years old. Willing to sign the informed consent form and agree to join the official LINE account to receive research tracking.  Exclusion Criteria:  Babies older than 5 months Co-morbid medical conditions of the baby such as chronic lung disease, cyanotic congenital heart disease, neuromuscular disease and a primary immunodeficiency. Family members who do not live with the Indicator case Family with grandparents younger than 65 years old Someone living with family members refuses to participate in the research. Unwilling to sign informed consent form or refuse to join the official LINE account to receive tracking.