Journal of Vaccine Research 2024, Vol.14, No.3, 107-119 http://medscipublisher.com/index.php/jvr 108 2 Epidemiology of Hepatitis B 2.1 Global prevalence and incidence Hepatitis B virus (HBV) infection remains a significant global health challenge, with an estimated 240 million people chronically infected worldwide (Ott et al., 2012; Lavanchy and Kane, 2016). The prevalence of chronic HBV infection varies significantly across different regions, with the highest endemicity observed in sub-Saharan Africa and East Asia, where prevalence rates can reach up to 8.6% (Ott et al., 2012). In contrast, regions such as North America, Western Europe, and parts of Latin America exhibit much lower prevalence rates, often below 2% (Ott et al., 2012; Razavi-Shearer et al., 2018). Despite a general decline in prevalence from 1990 to 2005, the absolute number of individuals living with chronic HBV infection has increased due to population growth, rising from 223 million in 1990 to 240 million in 2005 (Ott et al., 2012). The global burden of HBV is further underscored by the high mortality associated with the infection, with approximately 800 000 deaths annually, primarily due to liver cancer and cirrhosis (Lavanchy and Kane, 2016). The World Health Organization (WHO) has recognized viral hepatitis as a critical public health issue, ranking HBV as the 15th leading cause of death globally (Lavanchy and Kane, 2016). Efforts to combat HBV have led to significant reductions in prevalence among younger populations, particularly in regions with robust vaccination programs (Lavanchy and Kane, 2016). 2.2 Modes of transmission HBV is transmitted through parenteral or mucosal exposure to infected blood and body fluids. The primary modes of transmission include vertical transmission from mother to child during childbirth, horizontal transmission through close household contact, sexual contact, and unsafe medical practices such as unsterilized injections and blood transfusions (Shepard et al., 2006; Te and Jensen, 2010; Hwang et al., 2012). In highly endemic areas, vertical and early childhood horizontal transmission are predominant, leading to a high rate of chronic infection (Hwang et al., 2012). Conversely, in low endemic regions, transmission typically occurs in adulthood, often resulting in acute, self-limiting infections (Hwang et al., 2012). The risk of chronic infection is significantly higher when HBV is acquired during infancy or early childhood, with chronicity rates of up to 90% in perinatal infections compared to less than 5% in adult-acquired infections (Shepard et al., 2006). This highlights the critical importance of preventing mother-to-child transmission through timely birth-dose vaccination and the use of hepatitis B immunoglobulin (Shepard et al., 2006; Razavi-Shearer et al., 2018). 2.3 Regional variations The epidemiology of HBV infection exhibits considerable regional variation, influenced by factors such as vaccination coverage, healthcare infrastructure, and public health policies. In sub-Saharan Africa and East Asia, high endemicity rates are observed, with significant public health efforts focused on reducing mother-to-child transmission and improving vaccination coverage (Ott et al., 2012; Razavi-Shearer et al., 2018). In these regions, the implementation of universal infant vaccination programs has led to substantial declines in HBV prevalence among children (Lavanchy and Kane, 2016; Razavi‐Shearer et al., 2018). In Latin America, the pattern of HBV endemicity varies widely, with low prevalence in temperate South America and parts of the Caribbean, moderate prevalence in Brazil and Andean countries, and high prevalence in the Amazon basin (Oh, 1990). Strategies to combat HBV in this region emphasize the prevention of perinatal and early childhood transmission, alongside targeted vaccination of high-risk adult populations (Oh, 1990). In North America and Western Europe, HBV prevalence is generally low, attributed to effective vaccination programs, stringent blood screening practices, and public health education (Ott et al., 2012; Ott et al., 2012). However, these regions face challenges related to migration from high-prevalence countries, necessitating tailored public health responses to address the needs of immigrant populations (Locarnini et al., 2015). The global epidemiology of HBV is shaped by a complex interplay of demographic, socio-economic, and healthcare factors. Continued efforts to enhance vaccination coverage, improve diagnostic and treatment access,
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