Palivizumab, a monoclonal antibody against RSV, can be administered to prevent bronchiolitis to infants less than one year of age that were born very prematurely or that have underlying heart disease or chronic lung disease of prematurity. Passive immunization therapy requires monthly injections during winter. Otherwise healthy premature infants that were born after a gestational age of 29 weeks should not be administered palivizumab as the harms outweigh the benefits. Passive protection through the administration of other novel monoclonal antibodies is also under evaluation.