Journal of Vaccine Research 2024, Vol.14, No.3, 135-146 http://medscipublisher.com/index.php/jvr 142 In the initial stages, laboratory research and animal testing are conducted to evaluate the safety and bioactivity of vaccine candidates. Experiments are first performed on rats, and the efficacy of the vaccine is assessed through photomicrographs of the rat sciatic nerve stained with hematoxylin and eosin (Sellers et al., 2020) (Figure 1). Regulatory agencies such as the U.S. Food and Drug Administration (FDA) and the European Medicines Agency (EMA) require comprehensive data from these studies before allowing human trials to commence. Figure 1 Photomicrograph of sciatic nerve stained by hematoxylin and eosin from a Wistar (Han) rat administered ISCOMATRIX (Adopted from Sellers et al., 2020) Note: The image shows perineural infiltration of inflammatory cells due to the vaccine administered at or near the sciatic nerve. These inflammatory cells are clustered around the nerve, indicating a localized immune response triggered by the vaccination (Adapted from Sellers et al., 2020) Human clinical trials are conducted in three phases. Initially, small groups of healthy volunteers are tested to assess safety and dosage. In subsequent phases, larger groups are involved to further evaluate safety and immunogenicity, culminating in extensive studies involving thousands of participants to confirm the vaccine's efficacy and monitor for adverse effects. Regulatory bodies closely monitor these trials to ensure compliance with ethical and safety standards (Sellers et al., 2020). After successful clinical trials, vaccine developers submit a Biologics License Application (BLA) or Marketing Authorization Application (MAA) to regulatory authorities. These applications include all data from preclinical and clinical studies. Regulatory agencies then review the data to ensure the vaccine meets all safety and efficacy standards before granting approval for public use. Once a vaccine is approved, ongoing surveillance is conducted to monitor its safety in the general population. This includes reporting and analyzing adverse events through systems like the Vaccine Adverse Event Reporting System (VAERS) in the United States. Continuous monitoring helps to identify any rare or long-term adverse effects that may not have been evident in clinical trials (Leunda and Pauwels, 2019). 7.2 Ethical issues in vaccine development The ethical considerations in vaccine development are multifaceted, involving issues of trial design, informed consent, risk-benefit analysis, and equitable distribution. Ethical trials require that participants are fully informed about the potential risks and benefits of the vaccine. Informed consent is a cornerstone of ethical research, ensuring that participants voluntarily agree to take part in the trial with a clear understanding of what it involves. This is particularly challenging in resource-limited settings where literacy and healthcare access may be limited (Slack, 2016). Ethical vaccine trials must carefully balance the potential benefits of the vaccine against the risks to participants. This includes considering the severity of the diseases being prevented, the likelihood of adverse effects, and the overall public health impact. For instance, during the COVID-19 pandemic, the urgency to develop a vaccine had
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