20 Sep (OMSJ) – It is estimated that each year, 800,000 children die of pneumonia particularly in poor countries. The most common agent of pneumonia is Streptococcus pneumoniae, of which there are over 90 serotypes. These organisms may colonise the nose and throat without causing any disease. A few children suffer from invasive disease. Vaccines are available which cover some of the serotypes. Two types of vaccines are commonly used – the conjugate vaccine which is useful in children under 2 but less useful because they protect against 7 to 13 serotypes only, and a polysaccharide vaccine which cover 23 serotypes but not useful in children under 2 years. The conjugate vaccine given in children under 2 has been successful in reducing the incidence of vaccine strain invasive pneumococcal disease, in both vaccinated children and in the non-vaccinated older population. However, widespread use of the 7 valent vaccine in some countries has resulted in an increase in infections with non-vaccine strains (replacement strains) some 6 years later. Some of the replacement strains are resistant to the relatively inexpensive antibiotics like penicillin.
The investigators wanted to explore whether further vaccine pressure, from mass vaccination with PCV-7 of the whole population (including adults who are not usually the target population for the conjugate vaccine), would cause proliferation of replacement strains in the community.
To find out, investigators performed a cluster randomized trial. PCV was given to all children under 30 months of age. Older children and adults in some communities selected randomly received one dose of PCV-7 vaccine as study drug and control communities received meningococcal serogroup C conjugate vaccine. Cross-sectional surveys to collect nasopharyngeal swabs were conducted before vaccination and periodically after vaccination. Azithromycin (a drug also effective against pneumococcus) was given to this population in an unrelated programme and so this study was truncated after 2 years.
The investigators did not find any significant serotype replacement as a result of mass vaccination with PCV-7 over the 2 year study period. The ethical issue considered is whether a trial of this nature, that increases the chances of the spread of resistant strains in the community, can be justified in a poor country like Gambia. (See full report)