Journal of Vaccine Research 2024, Vol.14, No.3, 107-119 http://medscipublisher.com/index.php/jvr 113 responses in HBV transgenic mice (Buchmann et al., 2013). While HBV vaccines are generally effective, various factors can influence their efficacy. Addressing these challenges through higher doses, additional booster doses, the use of adjuvants, and the development of therapeutic vaccines can enhance the immune response and provide long-term protection against HBV infection. Figure 2 Flowchart of the study selection process (Adapted from Tian et al., 2021) Image caption: This chart illustrates the screening process for a systematic review and meta-analysis. Initially, 1 123 records were identified through database searching, and 27 additional records were identified through other sources. After removing duplicates, 576 records were left for screening. Following the screening, 574 records were excluded, leaving 32 articles for full-text assessment. After full-text assessment, 15 articles were excluded for specific reasons: 5 articles involved children and adolescents, 8 were retrospective studies, and 2 had repeated samples. Ultimately, 17 studies were included in the quantitative synthesis (meta-analysis). This chart clearly shows the entire process from the initial identification of records to the final inclusion in the meta-analysis, detailing each screening stage and the specific reasons for exclusion (Adapted from Tian et al., 2021) 6 Innovations and Advances in Vaccine Technology 6.1 Recombinant and DNA vaccines Recombinant DNA technology has revolutionized the development of hepatitis B vaccines. The first recombinant hepatitis B vaccine was produced by expressing the hepatitis B surface antigen (HBsAg) in yeast cells, specifically Saccharomyces cerevisiae. This method allowed for the large-scale production of vaccines without the need for human plasma, thereby reducing the risk of contamination with other pathogens (Zhang et al., 2019). The recombinant vaccine, Engerix-B, has shown excellent immunogenicity and protective efficacy in various populations, including neonates, children, and adults (Keating and Noble, 2003). Further advancements have led to the development of vaccines that include additional components of the hepatitis B virus, such as the Pre-S1 and Pre-S2 antigens. These components have been shown to enhance the immunogenic response, particularly in populations that are non-responsive to the conventional HBsAg-only vaccines. For instance, the Bio-Hep-B vaccine, which includes Pre-S1 and Pre-S2 antigens, demonstrated significantly higher immunogenicity and a more rapid antibody response compared to Engerix-B in neonates (Yerushalmi, 1997). DNA vaccines represent another innovative approach. These vaccines involve the direct introduction of plasmid DNA encoding the HBsAg into the host cells, leading to the production of the antigen and subsequent immune response. Preclinical studies have shown that DNA vaccines can induce potent and sustained immune responses,
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