Respiratory syncytial virus (RSV) is a common virus which, in most cases, causes mild, cold-like symptoms such as a sore throat, cough or a blocked nose. However, in young infants RSV can cause serious lung problems and in older adults and people with chronic medical conditions, RSV can worsen illnesses such as chronic obstructive pulmonary disease (COPD) and congestive heart failure (CHF). RSV can lead to hospitalisation in severe cases and in some cases it can be fatal.