Why is Phase 3 clinical trial of vaccine so important and how long will it take?

The COVID-19 pandemic has concerned everyone about the development of vaccines. Domestic vaccines have now entered Phase 3 clinical trials, and are only one step away from being put on the market. Many friends have asked Huazi, what is the use of Phase 3 clinical trials, is it really important, and how long will it take?

1. Clinical trials before drugs are put on the market Hua Zi said that vaccines are drugs, and the clinical trials of drugs are divided into phases 1, 2, 3, and 4. Phases 1, 2, and 3 clinical trials must be completed before the drug is officially put on the market. Phase 4 clinical trials are conducted after the drug is put on the market. Clinical trials are mainly used to study the efficacy and risks of drugs and provide reliable data support for market review.

Simply put, a drug needs to go through animal testing from the beginning of its development, and only after confirming its safety can it enter the human trial stage. The purpose of Phase 1 clinical trials is mainly to conduct safety evaluation. Because the drug acts on the human body, safety is required to be the first priority. At the same time, the metabolism and excretion pathways of the drug in the human body will also be examined.

Once the safety of a drug is confirmed in Phase 1 clinical trials, it will enter Phase 2 clinical trials. This stage is mainly to evaluate the effectiveness of the drug and observe safety more deeply. In Phase 2 clinical trials, the efficacy of the drug is evaluated and the specific dosage is determined.

After Phase 1 clinical trials have confirmed safety and Phase 2 clinical trials have confirmed effectiveness, Phase 3 clinical trials will begin. This phase is the most important stage before a drug is marketed, and a larger sample size (required to be more than 300 cases) and a longer observation period (usually 1 to 3 years) will be used to further verify the drug's efficacy and safety, evaluate the relationship between benefits and risks, and provide sufficient basis for the review of the drug's official launch.

2. The importance of Phase 3 clinical trials of vaccines Phase 3 clinical trials are very important for vaccines. Because vaccines are not like ordinary drugs, which are not as simple as simply verifying "effective", "ineffective" or "toxic", "non-toxic". It is also necessary to prevent the vaccine from producing "antibody-dependent enhancement (ADE) effect".

The effect of vaccines is that they can induce the human body to produce viral antibodies to resist viruses. The ADE effect means that under certain reasons, the viral antibodies produced by the human body will in turn help the virus invade cells.

The ADE effect was first observed in dengue virus. There are four serotypes of dengue virus. After being cured, some patients will be infected again if they come into contact with other serotypes of dengue virus. The original viral antibodies in their bodies will help the virus invade cells at a faster rate, which will aggravate the severity of the disease.

The novel coronavirus is highly variable, and humans have a "lack of imagination" about the development of the virus. For a vaccine that needs to be applied to hundreds of millions or even billions of people, there can be no risk at all. Therefore, a large-sample Phase 3 clinical trial is required to avoid ADE and other unknown adverse effects.

Phase 3 clinical trials of drugs are likely to be completed within 6 months, and usually require more than 1 year of observation to obtain information on safety and efficacy of long-term use. However, under the premise of increasing the sample size, the trial time can be shortened. Domestic vaccines have now signed Phase 3 clinical cooperation agreements with many countries, and the number of people enrolled in the vaccination has exceeded 20,000. More sample sizes and clinical data from different regions will speed up the process of vaccine launch.

For ordinary drug clinical trials, the time for market review is often longer than the test. However, due to the urgency of the demand for vaccines, the COVID-19 vaccine will definitely be given priority review. Based on this estimate, the domestic vaccine will most likely complete phase 3 clinical trials and reviews within 6 months and will be available on the market at the end of this year or early next year.

Vaccines are the result of the hard work of countless scientific researchers, and the Chinese vaccine vanguard is moving forward at full speed. However, "you can't eat hot tofu in a hurry", for absolute safety and effectiveness, everyone should be more patient, and before the vaccine is officially launched on the market, you still need to do a good job of personal protection and not take it lightly. I am pharmacist Huazi, welcome to follow me and share more health knowledge.