Efficacy of pneumococcal conjugate vaccines in large scale field trials.

Each year Streptococcus pneumoniae causes approximately 1.2 million deaths worldwide from pneumonia. In the United States S. pneumoniae is estimated to cause 500,000 cases of pneumonia and 7 million episodes of acute otitis media annually. The current pneumococcal polysaccharide vaccine is ineffective in children <2 years old and may not produce an adequate antibody response until children reach the age of 5 years. Pneumococcal conjugate vaccines are immunogenic after primary and booster vaccination in young children and in children and adults with immunodeficiencies. Immunization with conjugate vaccines also induces a strong and rapid anamnestic response and enhanced functional activity of antibodies. Two large scale field trials of pneumococcal conjugate vaccines were initiated in 1995, 1 in California and 1 in Finland. The California trial, involving 37,868 children, evaluated the efficacy of a 7-valent conjugate for the prevention of invasive pneumococcal disease and secondarily evaluated its efficacy for acute otitis media and pneumonia. Preliminary results indicate 94% efficacy against invasive pneumococcal disease caused by serotypes included in the vaccine in fully or partially vaccinated children. Preliminary evidence from large scale field trials indicates that pneumococcal conjugate vaccines are effective in reducing invasive pneumococcal disease as well as acute otitis media and pneumonia in children and represents a significant advance in the prevention of childhood infectious diseases.