Streptococcus pneumoniae are Gram-positive, lancet-shaped bacteria. There are more than 90 serotypes of S. pneumoniae, of which 4 account for most disease and drug-resistant. S. pneumoniae cause more than 80% of the cases of lobar pneumonia and the group are known in medical microbiology as the “pneumococcus”, referring to its morphology and its consistent involvement in pneumonia
Community-acquired pneumonia is the sixth leading cause of death in the USA and has a significant economic impact in terms of loss in work productivity and healthcare costs. Hospitalised patients are treated with intravenous antimicrobials, such as third-generation cephalosporins, tetracyclines, macrolide antibiotics or in cases where resistance is suspected, fluoroquinolones.
Those at greatest risk of infection with S. pneumoniae are the elderly, children greater than or equal to 2 years of age, blacks, and American Indians. People infected with HIV are at increased risk for serious pneumococcal infections, as are persons with underlying medical conditions interfering with immune responses.
According to the CDC, up until 2000, S. pneumoniae infections caused 100,000-135,000 hospitalizations for pneumonia, 6 million cases of otitis media, and 60,000 cases of invasive disease, including 3,300 cases of meningitis. The incidence of sterile-site infections showed geographic variation from 21 to 33 cases per 100,000 population. In 2002, the rate of invasive disease was 13 cases per 100,000 in the US. This reduction in cases reflects the introduction of conjugate vaccines.
Death occurs in 14% of hospitalized adults with invasive disease. Neurologic sequelae and/or learning disabilities can occur in meningitis patients. Hearing impairment can result from recurrent otitis media.
Of significant concern the US CDC found that the prevalence of drug resistant S. pneumoniae has been increasing in United States since 1987. Drug-resistant pneumococci cause at least 15,000 cases of meningitis, 7,000 cases of sepsis/bacteremia, 150,000 cases of pneumonia, and over 1,000,000 cases of otitis media annually. Between 3-35% of pneumococcal illness is due to drug-resistant strains and this proportion shows wide geographic and temporal variation.
The requirement in serious cases for intensive care, intravenous therapy and mechanical ventilation contributes to the significant healthcare costs incurred, which are estimated to be in the region of US$8.4 billion in the USA (Spiritus, 2000) or an average of US$14,294 per patient (Kaplan et al, 2002).
Wyeth recently launched their paediatric vaccine Prevnar, which is approved for use in children from 2 months-2 years and provides active immunisation against the 7 most common pneumococcal serotypes. This is priced at approximately UD$ 60 per dose in the UK, 4 doses of which are required at monthly intervals to provide full immunity. The price for this 4-dose series of Prevnar is as high as all other childhood vaccinations combined, and doubts have been raised as to the cost effectiveness of a programme. A recent cost-benefit analysis (Weycker et al, 2000) reported that routine vaccination appears to be cost increasing for children less than 2 years who require multiple doses, but cost saving for those aged 2 to 5 years who require only a single dose. Despite this, Wyeth sales of Prevnar increased 73% in 2001 to reach total sales of US$ 798 million.
The market size estimate of US$2,018 million provided in Table X below is based on all children in developed nations receiving a 4-dose course at a price of US$230, and all 65 year old receiving one dose of the adult vaccine priced at US$15-20.
Table X. Strep. Pneumoniae market size.