How vaccine are developed ?

Millions of people are safely vaccinated each year. the vaccine must undergo extensive and rigorous testing to ensure its safety before it can be included in a country's immunization program. the vaccine should be tested, An experimental vaccine will first be tested in animals to assess its safety. If the vaccine elicits an immune response, it will be tested in three phases in human clinical trials. In the first phase, Give the vaccine to a small number of people (volunteers) to test its safety dose as well as to make sure that it stimulates the immune system. In the second phase, Give the vaccine to several hundred volunteers and test it several times on different groups of people such as children and the elderly. to test the vaccine's safety and ability to stimulate the immune system. In the third phase, Give the vaccine to several thousand volunteers across multiple countries. and these trials can determine whether the vaccine protects against the disease. then should get approval from an official in each country. In conclusion, any vaccine must pass through phases, which are to be tested on animals before humans and then tested in a small group and then in a small group varied in age and sex, and then it is tested on a multiple countries, and in the end, it must obtain approval from an official in each country.