Protective efficacy of an inactivated Mycoplasma pneumoniae vaccine.

The protective efficacy of a formalin-inactivated Mycoplasma pneumoniae vaccine was evaluated in a double-blind fashion in 7,861 Marine Corps recruits at Parris Island, South Carolina. Vaccine, administered in a 1-ml dose by a jet-injection device, was glass-grown and contained 264 microgram of protein nitrogen/ml. Phosphate-buffered saline with formalin was injected as a control. Systemic reactions to injection were similar in both groups, but the percentage of vaccinees with erythema (51%) and induration (52%) at 24 hr was significantly greater than the percentage of controls (2%) with these reaction (P less than 0.001). Twenty-one (0.5%) of 3,930 vaccinees and 43 (1.1%) of the 3.931 placebo recipients were hospitalized with pneumonia (chi2=7.61; P less than 0.01). Ten of 21 vaccinees and seven of 43 controls with pneumonia had a positive pharyngeal culture for M. pneumoniae (chi2=1.69; P =0.20), and fourfold rises in titer of serum antibody were noted in five of 14 vaccinees and in 15 of 28 placebo recipients with pneumonia (chi2=7.90; P less 0.0005). Therefore, vaccine efficacy for M. pneumoniae-specific pneumonia was 42% as determined by cultures and 67% by serologic tests. The vaccine showed no protective efficacy for M. pneumoniae-specific bronchitis or for M. pneumoniae pharyngeal carriage in recrutis in training.