Step 1: Lab Discovery

Scientists design and study vaccine ideas in research labs. They test them in cells and sometimes in animals to see if they trigger an immune response. Only the most promising candidates move forward.

Step 2: Phase 1 Trials

A small group of healthy volunteers, often fewer than one hundred, receives the vaccine. The focus is on safety and checking whether the immune system responds the way scientists expect.

Step 3: Phase 2 Trials

Hundreds of people participate. Researchers test different doses to find the best amount and schedule. They also track common side effects such as soreness, fever, or tiredness.

Step 4: Phase 3 Trials

Thousands or even tens of thousands of volunteers are included. This is the key test of whether the vaccine prevents illness. Scientists compare people who get the vaccine with people who do not, while continuing to watch safety closely.

Step 5: Approval

Health authorities such as the U.S. Food and Drug Administration or the European Medicines Agency review all the evidence. Independent experts also check the data before a vaccine is licensed for use.

Step 6: Ongoing Monitoring

The work does not end at approval. Once a vaccine is in use, health agencies keep monitoring millions of people in real time. This step helps detect very rare side effects and ensures vaccines remain safe.

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