Reduced risk of hospital admission for childhood asthma among Scottish twins: record linkage study.

The reliability of surveillance systems can affect the observed effectiveness of public health interventions. H influenzae meningitis is a life threatening disease and most cases occur before the age of 2 years. In this study cases of H influenzae meningitis in this age group were those most likely to be missed. The publicity surrounding the launch of the vaccine and the national study of vaccine failures might have been expected to improve reporting efficiency. However, we found that the introduction of the vaccine was associated with significantly increased underreporting, perhaps because of factors such as complacency following the success of the vaccine in reducing the incidence of the disease or an assumption that reporting to the British Paediatric Surveillance Unit was sufficient. These findings are relevant as continuing surveillance is needed to assess the effectiveness of the programme, identify vaccine failures, and monitor changes in predominant strains of the organism. A meningococcal vaccine is being introduced into the immunisation schedule in the United Kingdom. To measure the impact of this and other new vaccines accurately, the quality of the data sources for communicable disease surveillance must be ensured.