Disease information Pneumococcus

The bacterium Streptococcus pneumoniae is the most common cause of severe pneumonia worldwide. It also causes meningitis, septicaemia, and ear infections.

Although estimates of its death toll are made difficult by various factors, the pneumococcus bacterium (Streptococcus pneumoniae) is thought to kill 1 million people worldwide each year. Most of these are young children and infants.

In developing countries, as many as one in every 10 deaths in young children is attributed to this infection. Although vaccines for adults and children aged two and over have been available for years, these have not been suitable for the babies and toddlers who are most vulnerable to the disease because they do not stimulate an appropriate immune response.

However, a new conjugate vaccine that is highly effective in infants has recently been approved for marketing by the Food and Drug Administration (FDA) in the United States, and several more are in late stages of development. But it is unclear whether these will be as effective in developing country settings.

Pneumococcal vaccines protect by stimulating antibodies against the specific polysaccharide (complex sugar) capsules that cover the bacteria. There are more than 80 specific pneumococcal capsular polysaccharides. The pneumococcal conjugate vaccine licensed by the US Food and Drug Administration stimulates the production of protective antibodies against the seven serotypes that most frequently cause invasive disease in the United States. However, this "7-valent" vaccine does not stimulate antibodies against two serotypes, 1 and 5, which together are thought to be responsible for 12%-25% of invasive pneumococcal disease in many developing countries.

With such countries in mind, researchers and the vaccine industry have developed 9-valent and 11-valent pneumococcal conjugate vaccines that stimulate antibodies against serotypes 1 and 5. These are now being evaluated in large-scale field trials in several countries in Africa, Asia and Latin America. Scientists and public health officials must for wait efficacy data to emerge from these trials before making recommendations about the use of the new pneumococcal vaccines among infants in developing countries.

For more information see

• http://www.niaid.nih.gov/dmid/gambia
  Official web site for the Gambia Pneumococcal Vaccine Trial.
  The Gambia PVT is the centerpiece of global efforts to determine the effectiveness of pneumococcal conjugate vaccines in developing countries. Its aim is to determine if child survival can be significantly improved by administration of 3 doses of 9-valent pneumococcal conjugate vaccine. The vaccine trial is being carried out as a collaborative effort of the Gambia Government, the MRC Laboratories in the Gambia and with the sponsorship of WHO, Gates CVP, USAID, and NIAID, and with technical support from CDC and the London School of Hygiene and Tropical Medicine.
  
  
• http://www.who.int/vaccines-diseases/research/mening.htm
  
  
• http://www.childrensvaccine.org/html/v_pneumo_qf.htm
  
  
• From the journal Clinical Infectious Diseases, January 2000: ’Which Pneumococcal Serogroups Cause the Most Invasive Disease: Implications for Conjugate Vaccine Formulation and Use’. A review by Hausdorff et al.
  Part I. (2000: 30: pp 100-121)
  Part II. (2000: 30: pp 122-140)

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