Despite the fact that respiratory syncytial virus (RSV) infection in infants and young children is a worldwide public health concern, the development of a safe RSV vaccine has been hampered by formalin-inactivated RSV-enhanced respiratory disease (ERD). A strategy to reduce over-reactive T cells and increase neutralizing anti-RSV antibodies should be considered when developing a safer yet effective RSV vaccine for children. The study previously demonstrated that adult mice immunized with RSV recombinant G protein plus low-dose Cyclosporine A (G+ CsA) could produce increased levels of antigen-specific T regulatory cells in the lungs after a subsequent RSV challenge, overcoming the ERD. Anti-RSV antibodies that were neutralizing and prevented viral infection were also elicited. In this study, researchers looked to see if a G+ CsA vaccine could protect infant mice from RSV infection without causing ERD. The findings demonstrated that the G+ CsA vaccine could prevent RSV infection while causing only a minor loss of body weight. Importantly, after the RSV challenge, lung tissues had nearly normal morphology and no mucus appearance. 

These findings show that the G+ CsA vaccine strategy provided comparable benefits in the neonatal prime and infancy boost models as it did in the adult mouse model. Since it prevents the devastating ERD, the G+ CsA immunization strategy is potentially safe and effective in neonates and infants.