ABSTRACT
Hepatitis is an inflammation of the liver, commonly caused by a virus, and is an important cause of mortality and morbidity worldwide. Hepatitis A and E viruses (HAV and HEV, respectively) usually cause self-limited infection. The patients completely recover from hepatitis A and E after a few weeks of the onset of the disease symptoms [1,2]. The HAV and HEV infections are especially prevalent in developing countries, where poor sanitation promotes transmission of these viruses. On the other hand, hepatitis B and C viruses (HBV and HCV, respectively), mainly transmitted via contaminated body fluids, may cause chronic disease and lead to more severe complications such as liver cirrhosis and hepatocellular carcinoma [3,4]. In any case, viral hepatitis has an important impact on public health and, although measures to control virus transmission have been used, vaccination is the most effective practice. Therefore, enormous efforts have been made to develop vaccines to prevent viral hepatitis. Currently, vaccines are available only against HAV and HBV. The first hepatitis vaccine available, against hepatitis B, was formulated using empty particles containing hepatitis B surface antigen (HBsAg) purified from plasma of patients. The use of this plasma derived vaccine raised concerns about its safety. With the advance of recombinant DNAmethodology, current HBV vaccine was developed by expressing HBsAg in yeast cells and, until 2007, when a vaccine against human papillomavirus infection was approved, it was the only recombinant vaccine available. Although this vaccine is highly immunogenic, offering protection to approximately 95% of vaccinees, some individuals do not respond or respond poorly, leading researchers to improve the current vaccine by adding other epitopes to the HBsAg and increase its immunogenicity.
