Respiratory tract infections are a major public health issue. Prevention in high risk populations relies mainly on vaccination against Influenza and S. pneumoniae. Vaccination of health-care workers is highly recommended, to decrease absenteism, but above all to protect high risk patients. New conjugate vaccines have shown their effectiveness in the paediatric population. In patients with chronic bronchitis or COPD, immunomodulatory agents (OM-85 BV) and anti-oxidants (NAC) are probably contributive in decreasing exacerbation rates. Inhaled corticosteroids decrease exacerbations in a well defined group of severe COPD. In patients with diffuse bronchiectasis, the immunomodulatory effect of macrolides, and the use of inhaled corticosteroids should be confirmed by larger clinical investigations.