Improving Vaccines Against Pneumococcal Disease

Streptococcus pneumoniae is far and away the most common cause of invasive bacterial meningitis, which although rare is most prevalent in children and has a 20% fatality rate. As a result, meningitis is the attention-grabbing pneumococcal disease which makes headline news, but pneumococci are also a leading cause of respiratory morbidity and mortality in the developing world, as well as a common cause of glue-ear or otitis media. Now, growing antibiotic resistance in this organism is concentrating attention on the need for effective vaccination strategies to combat the infection.

Because there are multiple disease-causing serotypes of S pneumoniae (greater than 83 at the last count), the development of an effective polysaccharide-based vaccine has been troublesome. Commercially-available preparations, such as Pasteur-Merieux Serums et Vaccins' Pneumovax (14 antigens) and its replacement Pneumovax II (23 antigens) offer a protective efficacy of up to 60%-70%, but have limitations.

The US Centers for Disease Control in Atlanta has studied the efficacy of antigen stimulation in children by several of the individual components of the 14-valent vaccine, and found a range of efficacies (between 15% and 85%). This vaccine and the 23-valent one are poorly immunogenic in infants and should not be used in those under two years of age. Furthermore, they do not stimulate a memory response and have a limited effect on nasopharyngeal carriage, the primary route of transmission for S pneumoniae. Some of the antigens also have low immunogenicity in adults.