Explanation of the different Covid vaccine Phases

Scientists are studying a new cell vaccine and then feeding it to animals like mice or monkeys to see whether it induces an immune response. We have confirmed active production of 91 preclinical vaccines.

Scientists provide a limited number of people with the vaccine to monitor for safety and dosage and to ensure that it activates the immune system.

Scientists offer the vaccine to hundreds of people who are divided into different groups, such as children and the elderly, to see if the vaccine is behaving differently. These experiments further test the efficacy of the vaccine and its potential to activate the immune system.

Scientists are offering the vaccine to thousands of people and waiting to see how many people got infected relative to the volunteers who received it. These trials will decide whether the vaccine offers protection against coronavirus. The F.D.A. said in June that in order to be deemed successful, a coronavirus vaccine would have to protect at least 50 per cent of vaccinated people. Even in Phase 3

EARLY OR LIMITED APPROVAL: China and Russia approved the vaccines without waiting for Phase 3 test results. Experts say there are significant risks to the hurried process.

Authorities in-country study the outcomes of the trials and determine whether or not to approve the vaccine. During a pandemic, prior to obtaining formal approval, a vaccine can receive authorisation for emergency use. Researchers continue to track people who receive it after a vaccine is approved to make sure it is safe and reliable.

Combining phases is one way to improve the production of the vaccines. For example, certain coronavirus vaccines are now being tested on hundreds of people for the first time, in phase 1/2 trials.