The vaccine is a substance used to stimulate the production of antibodies and provide immunity against one or several diseases, prepared from the causative agent of a disease. From the first vaccine against smallpox, there are individuals who die because of adverse effects, and toxicity increased in the individuals. In the past, about 1000 people for every 1 million people vaccinated for the first time experienced reactions. These reactions include a vigorous toxic or allergic reaction. Rarely people have had very bad reactions to the vaccine. So, researchers conduct the clinical trials and use transgenic animals to evaluate all the side effects and reactions that could be happening because of the vaccine and not occur to humans.

Clinical trials start when a vaccine candidate drug is identified for the first time by preclinical evaluations which could involve high thrown out screening and selection of the appropriate antigen to invoke an immune response. There are preclinical stages where we determine the drug should be given in the tablet or in injection form. Vaccine first tested for its adverse effect and immunogenicity (the ability of a foreign substance to provoke an immune response in the body of a human or animals) in primates and non-primates. Recent scientific advances use transgenic animals as a part of vaccine preclinical protocol in hopes to more accurately determine drug reaction in humans.

Phase one trials 

Include introducing the drug into the human population. This involves two groups from the target population, and in this trail let’s say each subject may be randomly given a new vaccine or control treatment (control treatment include placebo or adjuvant-containing vaccine) and after that researcher collects the data and estimate the protective efficacy (the ability to produce a desired or intended result) of the vaccine. Then observed differences in outcome between treatment and control groups.

phase one trials chart
Fig: The flow chart of clinical phase one trial

In phase one we introduced the new drug to a small group of healthy volunteers, by this we want to reduce the chances of serious adverse effects (SAE) by slowly increasing the drug dosage or frequency. Let’s say we take 10 healthy volunteers and each one gets the minimum dose to start an immune response. And then we can add subgroup as along the first group did not get SAE. The vaccination schedule is vary depending on the nature of the drug. This phase is important to get to know the adverse effect and the minimum dosage to invoke the immune system.

Phase two trials

Phase two depend upon immunogenic (the ability of a foreign substance to enter a person’s body and cause an immune response as by vaccination) once a person receives the injection their immune system will begin to create antibodies, which are special proteins created by the body that help protect us against infectious viruses and bacteria, and toxicity (how poisonous or harmful a substance can be when accumulated too much in the bloodstream leading to adverse effects on the body). Phase two consists of injecting the vaccine to new healthy hundreds of people to determine the reaction in more diverse. Only 33 percent of the medication moves on to phase three.

Phase three trials 

In this phase we continue to see the immunogenicity, SAEs and toxicity on a much larger scale. And know If the vaccine shown safe and effective against the disease then it will be submitted for approval and production. There been different agency to approved the drug in the United States, the Food and Drug Administration (FDA) is responsible for the approval of the vaccine.

The purpose of phase three is to evaluate how the new medication works in comparison to existing medications for the same condition. To do this investigator uses a process called randomization. Phase three trials are usually double-blind, which means that neither the participant nor the investigator knows which medication the participant is taking to eliminate bias when interpreting results.

If the investigators demonstrate that the medication is at least as safe and effective as others already on the market, the FDA will approve the medication.

Roughly 25 to 30 percent of medications move on to phase four.

Phase four trial       

In phase four clinical trail agency like the FDA has approved medication. This phase involves thousands of participants and can last for many years.

This give us the information about the medication’s long-term safety, effectiveness, and any other benefits.


Clinical trials and each phase are important in clinical research. They give us knowledge about the safety and effectiveness of new drugs or treatments to be properly assessed before being approved for use in the general public

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