Journal of Vaccine Research 2024, Vol.14, No.4, 170-182 http://medscipublisher.com/index.php/jvr 176 increased risk of severe dengue and hospitalization following vaccination, a risk that became more apparent during long-term follow-up (Hadinegoro et al., 2015). TAK-003, another prominent vaccine candidate, has shown a more consistent safety profile across different populations. In phase III trials, TAK-003 demonstrated low rates of adverse effects, which were comparable to those observed with placebo. Common side effects included mild to moderate fever, headache, and fatigue, with very few reports of severe adverse events. Importantly, TAK-003 did not show the same level of increased risk in seronegative individuals that was observed with Dengvaxia, suggesting it may be safer for broader use across different populations (Biswal et al., 2021). 5.2 Post-Licensure surveillance Post-licensure surveillance is crucial in assessing the real-world safety and effectiveness of vaccines after they have been approved for public use. For dengue vaccines, post-licensure monitoring has been particularly important due to the potential for adverse effects that may not be fully apparent during clinical trials. The most notable example of this is the post-licensure experience with Dengvaxia. After its approval, extensive surveillance revealed that the vaccine increased the risk of severe dengue in seronegative individuals, leading to hospitalization in some cases. This discovery led to significant changes in the recommended use of Dengvaxia, restricting its use to individuals who had previously been infected with dengue (Wichmann et al., 2017). The challenges of post-licensure surveillance include the need for robust monitoring systems in countries where dengue is endemic, many of which may lack the infrastructure to effectively track vaccine-related adverse events. Additionally, the long-term nature of dengue immunity and the potential for vaccine-induced enhancement of disease mean that surveillance must be maintained for many years after vaccination (Guy et al., 2018). Countries deploying dengue vaccines need to invest in or enhance their surveillance systems to detect and respond to any adverse events promptly. 5.3 Regulatory approvals and guidelines The regulatory approval process for dengue vaccines has been rigorous, reflecting the complexity of balancing efficacy with safety, especially given the concerns about vaccine-induced severe dengue. Dengvaxia was the first dengue vaccine to receive regulatory approval, with its initial licensure occurring in Mexico in 2015. Since then, it has been approved in several countries in Latin America and Asia, with regulatory agencies closely following the guidelines set by the World Health Organization (WHO). However, the approval of Dengvaxia came with stringent recommendations, particularly from the WHO, which advised that the vaccine be administered only to individuals with confirmed previous dengue infection (Hadinegoro et al., 2015). TAK-003, which is currently in late-stage clinical trials, is expected to seek regulatory approval soon. Its more favorable safety profile, particularly its performance in both seropositive and seronegative individuals, suggests it may face fewer restrictions upon approval. The WHO and other regulatory bodies will likely assess TAK-003 with particular attention to its long-term safety data, especially in diverse populations. The regulatory landscape for dengue vaccines is continually evolving as new data emerges from ongoing trials and post-licensure surveillance. The WHO has played a central role in setting global guidelines, ensuring that vaccines are deployed safely and effectively in populations at risk of dengue. Future regulatory approvals will likely continue to focus on ensuring that vaccines not only provide broad protection but also minimize the risk of severe outcomes in all populations. 6 Implementation and Public Health Impact 6.1 Challenges in vaccine deployment The implementation of dengue vaccines faces significant challenges, both logistical and perceptual, that can impact their success in reducing the burden of dengue. Logistically, the distribution of dengue vaccines, particularly in low- and middle-income countries where dengue is most prevalent, presents substantial difficulties. These regions often have limited healthcare infrastructure, making it challenging to reach rural or underserved
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