Naturally acquired immunity to pneumonia due to Mycoplasma pneumoniae.

The immunity to Mycoplasma pneumoniae was studied by periodic collection of sera up to 15 years after infection. Sera were tested for antilipid antibodies by complement fixation. Antibody levels remained elevated for two to nine years after pneumonia but usually fell sharply after the second year in persons with milder symptoms. Infection rates were at least six times higher in comparison groups than in previous pneumonia patients. Schoolchildren with serologic evidence of infection, but without pneumonia, during the 1966-1967 epidemic were not protected during the next epidemic (1974). Children with evidence of infection during the first two years of life were at no higher risk of clinical pneumonia (immunopathological response) at school age than those without previous known exposure. The current study suggests that naturally acquired infection induces partial immunity which lasts longer after pneumonia than after mild infections.