Journal of Vaccine Research 2024, Vol.14, No.3, 107-119 http://medscipublisher.com/index.php/jvr 114 and they have been evaluated in various animal models (Cove, 2014). Clinical trials have also demonstrated the potential of DNA vaccines to elicit protective antibody responses in human subjects who did not respond to conventional vaccines (Rottinghaus et al., 2003). 6.2 Novel delivery methods The delivery method of a vaccine can significantly impact its efficacy. Traditional intramuscular injections are effective but may not always be the most efficient or practical method, especially in resource-limited settings. Novel delivery methods are being explored to enhance the immunogenicity and ease of administration of hepatitis B vaccines. One such method is particle-mediated epidermal delivery (PMED), which involves the use of a gene gun to deliver DNA-coated particles directly into the skin. This method has shown promise in eliciting strong immune responses in individuals who were non-responsive to conventional hepatitis B vaccines (Rottinghaus et al., 2003). Another innovative approach is the use of live-attenuated bacteria as carriers for DNA vaccines. For example, a study demonstrated that a DNA vaccine delivered via live-attenuated Salmonella typhimurium induced a stronger cytotoxic T lymphocyte (CTL) response compared to traditional recombinant HBsAg vaccines (Woo et al., 2001). In vivo electroporation is another technique that has been used to enhance the delivery and efficacy of DNA vaccines. This method involves the application of electrical pulses to increase the permeability of cell membranes, thereby facilitating the uptake of DNA. Preclinical studies have shown that electroporation can significantly enhance the immunogenicity of DNA vaccines in both small and large animal models (Cova, 2014). 6.3 Therapeutic vaccines While prophylactic vaccines have been highly effective in preventing hepatitis B virus (HBV) infection, therapeutic vaccines are being developed to treat chronic HBV infections. Chronic HBV infection is characterized by weak and functionally impaired virus-specific immune responses, which contribute to the persistence of the virus. Therapeutic vaccines aim to stimulate these immune responses to achieve virus clearance. DNA-based therapeutic vaccines have shown promise in preclinical studies. These vaccines can induce potent immune responses and have been evaluated in various animal models, including mice, chimpanzees, and woodchucks. Strategies to optimize the efficacy of these vaccines include the use of genetic adjuvants, combination with antiviral drugs, and prime-boost regimens (Cova, 2014). One innovative therapeutic approach involves the use of mucosal immunization with DNA vaccines. A study demonstrated that an oral mucosal DNA vaccine delivered via live-attenuated Salmonella typhimurium induced a strong CTL response, which is crucial for the clearance of HBV from hepatocytes. This method may be particularly beneficial for chronic HBV carriers, as it minimizes the risk of side effects associated with humoral responses, such as serum sickness and immune complex deposition (Woo et al., 2001). In conclusion, the advancements in recombinant and DNA vaccine technology, novel delivery methods, and the development of therapeutic vaccines represent significant strides in the fight against hepatitis B. These innovations hold the potential to enhance vaccine efficacy, improve immunogenicity in non-responders, and provide new treatment options for chronic HBV infections (Mcaleer et al., 1984; Yerushalmi, 1997; Yap et al., 1992; Woo et al., 2001; Keating and Noble, 2003; Rottinghaus et al., 2003; Cova, 2014; Zhao et al., 2020). 7 Policy and Implementation Strategies 7.1 Global health policies The global health policies surrounding hepatitis B virus (HBV) control have been significantly shaped by the World Health Organization (WHO) and other international health bodies. The WHO's Global Hepatitis Program has provided a comprehensive framework for action, which has been instrumental in guiding national responses to HBV control (Locarnini et al., 2015). Universal vaccination programs have been a cornerstone of these policies, with 168 countries implementing such programs by 2019, leading to a substantial decrease in HBV-related morbidity and mortality (Zanetti et al., 2008; Pattyn et al., 2021). The WHO's 2016 global health sector strategy on viral hepatitis aims for a 90%
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