Before a vaccine is approved for public use, it must pass through several phases of clinical trials. These trials are designed to evaluate the vaccine's safety, immunogenicity, and efficacy. Phase I trials focus on safety and typically involve a small group of healthy volunteers. Phase II trials involve a larger group and assess the vaccine's immunogenicity and optimal dose. Phase III trials are conducted on thousands of participants to confirm efficacy and monitor for adverse effects. Post-marketing surveillance (Phase IV) continues to monitor the vaccine's safety in the general population.
