Field trial of an inactivated Mycoplasma pneumoniae vaccine. I. Vaccine efficacy.

The efficacy of an inactivated Mycoplasma pneumoniae vaccine was evaluated in a double-blind study of 7,861 Marine Corps recruits at Parris Island, South Carolina. Vaccine was administered to half for the volunteers in a 1-ml dose by a jet-injection device, and phosphate-buffered saline was administered similarly to control subjects. Twenty-one vaccinees (5.3 per 1,000) and 43 recipients of placebo (10.9 per 1,000) were hospitalized with pneumonia; the incidence of illness among the two groups indicated a 51% overall protective efficacy for the vaccine (x2 = 7.49; P less than 0.01). The refined data for pneumonia due to M. pneumoniae showed 67% protective efficacy when serologic data were employed (x2 = 7.84; P = 0.005) and a 42% protective efficacy (x2 = 1.80; P greater than 0.10) when data from cultures for M. pneumoniae were employed. Vaccinees with pneumonia due to M. pneumoniae suffered no increased illness compared to controls, suggesting no hypersensitization with natural illness following the inactivated vaccine. Only when serologic data were analyzed did it appear that the M. pneumoniae vaccine protected against M. pneumoniae specific bronchitis (35% efficacy) but the difference was not statistically significant (x2 = 1.28; P greater than 0.20).