Journal of Vaccine Research 2024, Vol.14, No.3, 135-146 http://medscipublisher.com/index.php/jvr 137 Antigen-presenting cells (APCs) such as dendritic cells play a crucial role in bridging innate and adaptive immunity. APCs process antigens and present them to T cells, initiating the adaptive immune response. This process involves the expression of major histocompatibility complex (MHC) molecules on the surface of APCs, which present antigen fragments to T cells, leading to their activation. Recent advances in immunology have led to the development of subunit vaccines, which use pieces of the pathogen (such as proteins or polysaccharides) to stimulate an immune response without causing disease. These vaccines often require adjuvants to enhance their immunogenicity because the antigen alone may not elicit a strong enough immune response (Gause et al., 2017). Immunoinformatics has further advanced vaccine design by identifying highly immunogenic regions of pathogens, enabling the creation of more effective vaccines (Kazi et al., 2018). Understanding these immunological principles is essential for the rational design of combination vaccines, which aim to combine multiple antigens into a single formulation, providing broader protection while simplifying immunization schedules (Nauta, 2020). 3.2 Rationale for combination vaccines The rationale for developing combination vaccines includes several immunological and practical considerations, such as enhanced immunogenicity, reduction in the number of injections, synergistic effects, cost-effectiveness, and simplified logistics. Combining multiple antigens can enhance the overall immune response. When the immune system encounters a combination of antigens, it may be more comprehensively stimulated, resulting in stronger and more durable immunity. Studies have shown that combination vaccines can induce higher levels of antibodies and broader immune responses compared to single-antigen vaccines (Esteves-Jaramillo and Schmitt, 2022). This enhanced immunogenicity is crucial for providing effective protection against multiple diseases. Reducing the number of injections is another significant advantage of combination vaccines. Fewer injections simplify vaccination schedules, which improves compliance and coverage rates, particularly in pediatric populations. For example, the DTaP5-HBV-IPV-Hib pediatric hexavalent combination vaccine protects against six diseases with a single injection, reducing the number of visits and discomfort for children (Obando-Pacheco et al., 2019). Combination vaccines can also exhibit synergistic effects, where the combined immune response is greater than the sum of the individual responses. For instance, the HEV-FMDV combined vaccine demonstrated enhanced immunogenicity compared to the separate vaccines, indicating that different antigens can interact to produce a stronger immune response (Liu et al., 2019). This synergy can improve the overall efficacy of the vaccine. Cost-effectiveness is another critical consideration. Fewer injections mean fewer healthcare visits, reduced administration costs, and decreased logistical complexity in vaccine delivery programs. This not only alleviates the burden on healthcare systems but also reduces the economic impact on patients and families (Shende and Waghchaure, 2019). Combination vaccines simplify logistics by reducing the risk of administration errors and streamlining storage and distribution. With fewer vials and doses to manage, healthcare providers can ensure that patients receive the correct vaccinations at the appropriate times, improving the overall efficiency of immunization programs (Esteves-Jaramillo and Schmitt, 2022). In summary, combination vaccines offer numerous advantages, including enhanced immunogenicity, reduced number of injections, synergistic effects, cost-effectiveness, and simplified logistics. These benefits make combination vaccines an effective and economical public health tool, increasing vaccination coverage and reducing disease burden. 4 Components of the Five-in-One Vaccine 4.1 Individual vaccine components The five-in-one vaccine, also known as the pentavalent vaccine, combines five different antigens to provide comprehensive protection against diphtheria, tetanus, pertussis, hepatitis B, and Haemophilus influenzae type b (Hib). Each component plays a critical role in stimulating the immune system to recognize and combat these diseases. Diphtheria is caused by Corynebacterium diphtheriae, which produces a potent toxin. The diphtheria toxoid, a chemically inactivated toxin, elicits an immune response that neutralizes the toxin, preventing disease (Obando-Pacheco et al., 2019). Tetanus, caused by Clostridium tetani, leads to severe muscle spasms and can be fatal. The tetanus toxoid is also an inactivated toxin that induces immunity by prompting the body to produce antibodies that neutralize the tetanus toxin (Esteves-Jaramillo and Schmitt, 2022).
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