Surveillance of hepatitis B: an example of a vaccine preventable disease

The objectives of surveillance for vaccine preventable disease vary with th e stage of the vaccination programme. Pre-implementation data is required t o estimate the burden of disease and to decide on the appropriate vaccinati on strategy. Postimplementation data is required to monitor effectiveness b ut when high coverage is achieved surveillance must be able to accurately i dentify remaining pockets of susceptible persons. Sources of data include c linical and laboratory reporting. In most countries, all vaccine preventabl e diseases (including acute viral hepatitis) are notifiable by law. Such sy stems are prone to under-reporting but are usually satisfactory for monitor ing trends. To encourage the rapid tracing and vaccination of contacts of a cute hepatitis B, a sensitive case definition and timely reporting system a re required. A clinical definition (e.g. for viral hepatitis may be too bro ad, however, to assess the impact of vaccination and additional laboratory criteria may be necessary. As a country nears elimination, the predictive v alue of any case definition will fall and laboratory confirmation will alwa ys be required to target policy appropriately. Serological surveillance is another method for estimating disease incidence. This may be useful for hep atitis B as tests can distinguish vaccine induced immunity from natural inf ection and acute from prevalent cases. To monitor vaccine impact, age-coded specimens can be collected on an intermittent basis. Where the incidence i s low, however, this approach will be very expensive. Surveillance of vacci ne preventable disease therefore requires flexible surveillance systems whi ch are able to adapt to changes in incidence of infection and in control po licy. The use of multiple data sources and supportive information from spec ial studies is essential for the valid interpretation of routine data. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.