Hepatitis B is an infectious disease, which has a global occurrence and which causes substantial morbidity and mortality. Recent estimates show that 1/3 of the world's population has ever been exposed to the hepatitis B virus (HBV), that 367 million people are HBV carriers, and that hepatitis B causes 600,000 deaths each year. Yet hepatitis B is prevenatble by vaccination. Therefore, the World Health Organization (WHO) has incited to incorporate hepatitis B vaccination into the existing vaccination programmes, sinds 1997.
In the year 2000, after having reviewed the data on the persistence of vaccine-induced antibodies and on the cellular-mediated immunity after vaccination against hepatitis B, and in view of the absence of reports of clinical cases of hepatitis B in vaccinated persons, an expert group reached a consensus that there is no need for hepatitis B booster vaccination. Vaccine-induced protection is assumed to last life-long, conditional on an adequate immune response after a complete series of hepatitis B vaccines in a healthy person.
Nevertheless, the exact duration of protection after vaccination remains unknown, despite the availability of hepatitis B vaccines for over 20 years. Since universal hepatitis B vaccination has been implemented 168 countries (mostly in newborns and infants), knowledge on the duration of protection is currently needed.
This research project aims to augment this knowledge, by measuring the anti-HBs antibody levels in a time series (up to 15 years) of annual blood samples of adults who have been fully vaccinated against hepatitis B and who have received their last dose at least 5 years ago.
In addition, the hepatitis B-specific immune memory will be determined - both anti-HBs producing B-lymphocytes and hepatitis B-specific T-helper type 1 and type 2 memory T-lymphocytes - and the seroconversion for anti-HBc antibodies and HBsAg antigen during the follow-up period will be assessed. These data will also be used to study which variables influence the presence and/or the magnitude of HBsAg-specific cellular-mediated immunity, and to study the correlation between humoral and cellular immunity.