Presence of anti-HBs antibodies in blood donors 18-22 years after vaccination and implications for the selection of candidates for plasmapheresis for the production of hyperimmune plasma.

Abstract

Hepatitis B virus (HBV) infection is one of the major causes of human morbidity and mortality. It is estimated that at least two billion people are infected worldwide and that more than 350 million are chronic virus carriers; 4.5 million people develop new infections every year, of whom 15–40% will develop cirrhosis, various liver diseases, and hepatocellular carcinomas1. In addition to measures aimed at improving socioeconomic conditions and hygiene standards (the screening of blood units and blood components, the disinfection and sterilisation of medical and surgical instruments, the introduction and use of disposable equipment, and environmental and hospital education campaigns), the implementation of the mass vaccination programmes recommended by the World Health Organization (WHO) since 1992 has dramatically decreased the incidence of HBV infection among children and adolescents2,3. As early as 1983, some Italian regions began selective vaccination of people at risk, including intravenous drug users, male homosexuals, people with multiple sex partners, the life partners of HB surface antigen (HBsAg)-positive patients, haemophiliacs, and newly born babies of HBsAg-positive mothers. In 1991 (with Law N. 165 of 27 May 1991, published in the Official Gazette of the Italian Repreprintlic, 1st June 1991), in addition to maintaining selective vaccination of people at risk, vaccination was made compulsory for all children aged 12 years old (limited to the first 12 years of application) and infants in their first year of life4,5, with the aim of creating immunity in childhood or adolescence in order to protect adults whose lifestyles or occupations may increase the risk of infection. By the end of 2010, more than 20 million children had been vaccinated6 and coverage was 95.3% in 20137. This vaccination campaign therefore created two vaccinated populations: those vaccinated at the age of 12 years and those vaccinated during the first year of life. Numerous studies have been carried out in order to assess and confirm the effectiveness of the vaccination8. Post-vaccination anti-HBs antibody levels of ≥10 mIU/mL are generally considered to be protective8 but, although titres decline over time to undetectable values, this does not indicate a loss of protection and booster vaccine doses are not recommended8–11. Anti-HBs titres and their persistence depend on the number of doses received, the vaccine type, and the route and timing of administration6,8,9,12,13. It has been also observed that lower values are found in subjects vaccinated as infants than in those vaccinated after the first year of life6,9,14. The relative immaturity of the infant immune system could explain the weaker antibody response in subjects vaccinated as infants than in those vaccinated after the first year of life14. However, it is still generally agreed that, regardless of the time of administration, the vaccination induces long-term protection and that there is no need for additional booster doses8,9. On the other hand, antibody levels in young adults may be important in the field of transfusion as it is necessary to identify donors with high anti-HBs titres (after a booster vaccine dose) for the production of anti-HBs hyperimmune plasma15. The aim of this study was to evaluate antibody levels in blood donors 18–22 years after they had been vaccinated during the first year of life or at the age of 12 years.