Journal of Vaccine Research, 2025, Vol.15, No.1, 34-44 http://medscipublisher.com/index.php/jvr 37 research has achieved new results. For instance, adenovirus vectors that are not human have been used to bypass the original immune response in the human body. Moreover, amplification RNA technology and chimeric capsid technology have been developed to make vaccines safer and enhance the immune effect (Boulton et al., 2021; McCann et al., 2022; Wang et al., 2023; Sayedahmed et al., 2025; Tang et al., 2025). 3.3 Key factors influencing vaccine strategies Safety is the most important consideration when developing vaccines. Technologies such as inactivated vaccines and subunit vaccines usually rarely cause adverse reactions. However, the safety of viral vector vaccines and mRNA vaccines in large-scale trials is basically acceptable. Only occasionally, some serious adverse reactions have been reported, such as inflammatory reactions related to vectors, so continuous observation is needed (Kanokudom et al., 2021; Logunov et al., 2021). The immune effect and protection duration of a vaccine are the key factors determining whether a vaccine can be successfully promoted. Viral vector vaccines and mRNA vaccines are highly efficient in stimulating antibody and T-cell immune responses, which is of great significance for long-term protection. Just like the COVID-19 vaccine, getting a booster shot can further enhance and prolong the immune effect. When choosing vaccine technology, designing antigens and determining delivery methods, these factors need to be comprehensively considered in order to better resist various constantly mutating vector-borne pathogens (Logunov et al., 2020; Boulton et al., 2021; Tang et al., 2025). 4 Case Studies on Vaccine Development 4.1 Dengue fever The first approved dengue vaccine, CYD-TDV (Denvaxia), is only available to children aged 9 to 16 who have previously had dengue fever in areas with a high incidence of dengue fever. However, after its approval, this vaccine has been highly controversial because there is a risk of antibody-dependent enhancement (ADE) after being administered. If people who have never had dengue fever get vaccinated with this vaccine, their symptoms may become even more severe if they contract dengue fever in the future. Precisely because of this, there are many strict restrictions on the use of this vaccine, which also indicates that the immune principle of dengue fever is particularly complex (Figure 2) (Mourosi et al., 2022; Huang et al., 2023). New candidate vaccines like TAK-003 and other attenuated live vaccines are currently undergoing late-stage clinical trials and are expected to offer more comprehensive and safer protection in the future. These candidate vaccines are dedicated to solving a difficult problem, which is to ensure that the vaccines can generate a balanced immune response against four different types of dengue virus. Incomplete or unbalanced immune responses can increase the risk of ADE and also reduce the efficacy of vaccines. The interaction among different virus types and the development of vaccines that can provide people with strong, long-lasting and balanced immunity remain the main difficulties in the research and development of dengue fever vaccines (Redoni et al., 2020; Huang et al., 2023). 4.2 Malaria The RTS, S/AS01 vaccine is an important achievement in the research and development of malaria vaccines and also the first malaria vaccine to be applied on a large scale. However, its protective effect is average and weakens over time. At the same time, four doses are required and the process is complex, which limits its greater role in areas with a high incidence of malaria. Some good data have emerged from the newly developed R21 vaccine, with better protective effect and possibly longer protection time, bringing new hope for the effective control of malaria (Zhang, 2024). Although these achievements have been made, to significantly reduce the incidence of malaria, it is still necessary to use malaria vaccines in combination with existing prevention and control measures, such as controlling mosquito transmission and drug prevention. When promoting the malaria vaccine, there are still many troubles, such as inconvenient transportation and storage, too high price, and a reliable public health system is needed to ensure that the vaccine can reach everyone and also make people willing to get vaccinated (Al-Osaimi et al., 2024).
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