Prevention strategies for respiratory syncytial virus: passive and active immunization.

Prevention of respiratory syncytial virus (RSV) disease may ultimately be possible with active immunization, although no vaccine is currently available. Formalin-inactivated RSV vaccine caused serious disease in some recipients re-exposed to RSV, which slowed vaccine development. Current RSV vaccine candidates include RSV fusion protein vaccines, chimeric fusion protein-glycoprotein vaccines, and various live, attenuated RSV vaccines. RSV vaccines may be problematic in very young infants and newborns because of the relatively poor immunogenicity of most vaccine candidates to date. Passive immunization with human polyclonal intravenous immune globulin and humanized monoclonal antibody directed against the conserved fusion protein of RSV prevents severe RSV disease, although not necessarily viral infection. The humanized RSV monoclonal antibody is licensed for use in premature infants and infants with bronchopulmonary dysplasia and is being evaluated in infants with cardiac disease. Another innovative approach to prevent RSV disease in young infants is maternal immunization with a vaccine such as the purified fusion protein vaccine. Such a vaccine could stimulate antibody response to RSV surface glycoproteins and potentially prevent RSV disease in the mother, while maternal antibodies produced could be passively transmitted across the placenta to the infant. A pilot study in postpartum women demonstrated immunogenicity with no significant adverse reactions.