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In attempts to stimulate local respiratory tract immunity to respiratory syncytial virus (RSV), a temperature-sensitive mutant of RSV strain A2 (ts-1 mutant) was administered to 32 infants and children. Evidence of infection was demonstrated in all and no illness accompanied infection in children who had prior experience with RSV. Mild rhinitis occurred in seven infants without prior RSV experience and otitis occurred in one of these individuals. Also, genetically altered virus was recovered from some children but this type of virus represented less than 0.1% of virus recovered from the respiratory tract. An ideal RSV mutant would infect without undergoing such reversion or other genetic change and without producing clinical findings such as otitis which would not be acceptable for a vaccine designed for widespread use.
Kim et al. (Sun,) studied this question.