Vaccination
Vaccine development and approval

Just like any medication or procedure, no vaccine can be 100% safe or effective for everyone because each person's body can react differently. While minor side effects, such as soreness or low grade fever, are relatively common, serious side effects are very rare and occur in about 1 out of every 100,000 vaccinations and typically involve allergic reactions that can cause hives or difficulty breathing.

However, vaccines are the safest they ever have been in history and each vaccine undergoes rigorous clinical trials to ensure their safety and efficacy before approval by authorities such as the US Food and Drug Administration (FDA).

Prior to human testing, vaccines are tested on cell cultures and the results modelled to assess how they will interact with the immune system. During the next round of testing, researchers study vaccines in animals, including mice, rabbits, guinea pigs, and monkeys. Vaccines that pass each of these stages of testing are then approved by the public health safety authority (FDA in the United States) to start a three-phase series of human testing, advancing to higher phases only if they are deemed safe and effective at the previous phase. The people in these trials participate voluntarily and are required to prove they understand the purpose of the study and the potential risks.

During phase I trials, a vaccine is tested in a group of about 20 people with the primary goal of assessing the vaccine's safety. Phase II trials expand the testing to include 50 to several hundred people. During this stage, the vaccine's safety continues to be evaluated and researchers also gather data on the effectiveness and the ideal dose of the vaccine. Vaccines determined to be safe and efficacious then advance to phase III trials, which focuses on the efficacy of the vaccine in hundreds to thousands of volunteers. This phase can take several years to complete and researchers use this opportunity to compare the vaccinated volunteers to those who have not been vaccinated to highlight any true reactions to the vaccine that occur.

If a vaccine passes all of the phases of testing, the manufacturer can then apply for license of the vaccine through the relevant regulatory authorities such as the FDA in US. Before regulatory authorities approve use in the general public, they extensively review the results of the clinical trials, safety tests, purity tests, and manufacturing methods and establish that the manufacturer itself is up to government standards in many other areas.

After regulatory approval, the regulators continue to monitor the manufacturing protocols, batch purity, and the manufacturing facility itself. Additionally, vaccines also undergo phase IV trials, which monitor the safety and efficacy of vaccines in tens of thousands of people, or more, across many years.
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