Research led by Johns Hopkins Children's Center scientists has figured out why a respiratory syncytial virus vaccine used in 1966 to inoculate children against the infection instead caused severe respiratory disease and effectively stopped efforts to make a better one. The findings, published online on Dec. 14 in Nature Medicine, could restart work on effective killed-virus vaccines not only for RSV but other respiratory viruses, researchers say. The new findings also debunk a popular theory that the 1966 vaccine was ineffective because the formalin used to inactivate the virus disrupted critical antigens, the substances that stimulate the production of protective antibodies.