What are your concerns?

Hard to understand


Or copy link


Vaccine Testing: How Is It Done?

Vaccine Testing: How Is It Done?

Recently, a number of experts shared their doubts on the effectivity and safety of a Russian-made vaccine against COVID-19. These experts claim that the development of the vaccine was rushed, and because of this, people have started asking about what are the phases of vaccine development.

Vaccine development is not as simple as creating a vaccine, testing it, and then releasing it to the public. Vaccines need to go through very rigorous and complex testing methodologies that test not just the effectivity, but also the safety of the vaccine.

Researchers can’t simply fast-track the testing because people’s lives depend on this vaccine. They need to test the vaccine thoroughly, in order to understand the effects on the human body, as well as how safe it would be.

But what are the phases of vaccine development, and why does it take such a long time to complete?

How Do Vaccines Work?

What are the phases of vaccine development?

There are 5 main stages when it comes to vaccine development. The preclinical stage, which is then followed by the phase 1 trials, phase 2 trials, phase 3 trials, and then finally, approval.

Researchers will need to test their vaccines in all of these stages to ensure that it is safe for use. Here’s a breakdown of each stage:

Preclinical Stage

The preclinical stage is the very first stage of vaccine testing. During this stage, researchers test an initial form of the vaccine on animals. Human testing is not yet allowed at this stage, since this will essentially be the very first time the vaccine will be tested on a living organism.

The most common test animals are monkeys and mice. Testing the vaccine on these animals can help researchers get an idea of how the vaccine would behave in humans, how effective it would be, as well as any possible side effects it could have.

However, there are some researchers who are conducting the preclinical stage without any form of animal testing. In fact, some researchers developing a COVID-19 vaccine have opted out of animal testing completely.

These non-animal forms of testing are relatively new, and researchers are hopeful that this will be the norm in the future.

Animal rights groups are also supporting these forms of testing, as it poses no risk to animals.

Phase 1 Trials

After the preclinical stage, the phase 1 trials will start. During the phase 1 trials, researchers would give an initial formulation of the vaccine to a small number of people. This helps give the researchers an idea of the possible effects of their vaccine, as well as how effective it would be when injected into people.

During this stage, researchers will also figure out the dosage required for the vaccine to be deemed effective.

Phase 2 Expanded Trials

Next up in the phases of vaccine development is the phase 2 expanded trials.

As the name suggests, this expands upon the trials that were done during the first phase of vaccine development.

Researchers will administer the vaccine to hundreds of people of various demographics. Usually, researchers give the vaccine to people of different age groups.

This gives the researchers a clear picture of how the vaccine can have a different effect from person to person. The reason for this is that the vaccine might behave differently when given to a child, an adult, or to the elderly.

This paints a clearer picture of how the vaccine would affect a person’s immune system, as well as how effective it would be against the illness.

In some situations, such as with COVID-19, the first and second phase are usually combined. This is a way to accelerate development for testing.

Phase 3 Efficacy Trials

Fourth in the phases of vaccine development are the phase 3 trials. During the phase 3 trials, researchers will administer the vaccine to an even larger amount of people, usually thousands of people.

Along with the vaccine, volunteers will also be given a placebo. The phase 3 efficacy trials help give researchers a better idea of how effective their vaccine would be.

As the sample size is now in the thousands, the results are much more reliable, especially since it will be tested against a placebo.

According to the United States FDA, their requirement for an effective COVID-19 vaccine would be a vaccine that can protect at least 50% of vaccinated people. This means that the results of the phase 3 trials should be 50% or more for it to be deemed effective in the USA.


The last phase is the approval stage. During this stage, the vaccine has already been approved for use by the general public. This means that it is already available for purchase, and has undergone all of the necessary tests and procedures.

While the vaccine is considered effective at this stage, researchers will still continue monitoring the results. This helps them get a better understanding of the vaccine, as well as the long-term effects of it on humans.

Key Takeaways

The important thing to know about these steps is that these are all necessary. Researchers cannot skip any of these phases, because human lives are at stake.

This is also the reason why some experts are apprehensive about the fast-tracked development for some COVID-19 vaccines. The vaccine might be effective for the short-term, but some people might suffer problems in the long run.

That’s why it is still important for people to practice the precautionary measures against COVID-19. This can help stop the spread of the virus, and can potentially prevent future outbreaks.

Learn more about COVID-19, here.

Hello Health Group does not provide medical advice, diagnosis or treatment.


Vaccine Development, Testing, and Regulation | History of Vaccines, https://www.historyofvaccines.org/content/articles/vaccine-development-testing-and-regulation, Accessed August 17 2020

Coronavirus Vaccine Tracker – The New York Times, https://www.nytimes.com/interactive/2020/science/coronavirus-vaccine-tracker.html, Accessed August 17 2020

Making Vaccines: Process of Vaccine Development | Children’s Hospital of Philadelphia, https://www.chop.edu/centers-programs/vaccine-education-center/making-vaccines/process-vaccine-development, Accessed August 17 2020

Vaccine Testing and Approval Process | CDC, https://www.cdc.gov/vaccines/basics/test-approve.html, Accessed August 17 2020

Stages of Vaccine Development – The Children’s Vaccine Initiative – NCBI Bookshelf, https://www.ncbi.nlm.nih.gov/books/NBK236428/, Accessed August 17 2020

Evaluation for SARS-CoV-2 Testing in Animals | CDC, https://www.cdc.gov/coronavirus/2019-ncov/animals/animal-testing.html, Accessed August 17 2020

NGO: Covid-19 research is opportunity to progress non-animal methods, https://chemicalwatch.com/122708/ngo-covid-19-research-is-opportunity-to-progress-non-animal-methods, Accessed August 17 2020

Picture of the authorbadge
Written by Jan Alwyn Batara Updated May 26
Medically reviewed by Mia Dacumos, M.D.