Coronavirus Resources Trending Health Stories

How Vaccines for Coronavirus Were Made

A woman in her kitchen and drinking coffee while on her laptop
Choose the health content that's right for you, and get it delivered right in your inbox

Researchers and scientists were quickly able to create a vaccine to start protecting people against COVID-19. Although creating a new vaccine can sometimes take years, the U.S. Department of Health and Human Services (HHS) was able to speed up the process of developing and manufacturing vaccines to prevent more cases of COVID-19. Here’s how that process works.

How Do Vaccines Work?

The first step in developing a vaccine is understanding how the vaccine will work to prevent infection. Some of the vaccines currently being distributed are made from synthetic messenger RNA. mRNA is used to trigger the body’s immune system to produce protective antibodies without using the actual virus.

While vaccines for some other illnesses — such as the varicella (chickenpox) vaccine — actually use bits of the virus in the vaccine to create what’s called a “live virus vaccine,” the COVID-19 vaccines currently being distributed do not contain a live virus.

Instead, the two-dose vaccines from Pfizer and Moderna essentially work by using synthetic mRNA to direct the body to produce a small amount of the spike protein. Once the vaccinated person’s immune system detects this protein, their body begins producing protective antibodies to defend against coronavirus.

Experts say that the protective antibodies will recognize and prevent COVID-19 from getting into the body’s cells in the future, should that person be exposed to coronavirus.

The single-dose COVID vaccine from Johnson & Johnson does not contain mRNA. It is instead known as a viral vector vaccine, using a common cold virus called adenovirus 26.

With the Johnson & Johnson vaccine, a small amount of genetic material that codes for a piece of coronavirus is mixed with a weakened version of adenovirus 26. The adenovirus brings the genetic material from the coronavirus into human cells, causing them to create a piece of the coronavirus spike protein.

How Does Your Immune System Respond to a Vaccine?

Once the vaccine is injected into your body, your immune system reacts by producing antibodies to the disease — the same sort of reaction it would have if you were exposed to the disease. But with a vaccine, you develop an immunity to the disease without actually getting that disease.

Although vaccines can have side effects, such as a low-grade fever or pain where you had the injection, they are usually mild and go away on their own. It’s very rare for a vaccine to cause severe side effects that last a long time.

What Other Ingredients Are in Vaccines?

In addition to the virus that causes the disease, there are other important ingredients in vaccines that help ensure their effectiveness and safety. These ingredients may include adjuvants that help increase your immune system’s response to the vaccine and stabilizers that help keep the vaccine effective after it’s made.

How Are Vaccines Developed?

Although creating a new vaccine can sometimes take years, many pharmaceutical companies were able to quickly advance their development and distribution processes. Part of the speed is due to the use of the Emergency Use Authorization (EUA) process. EUA means the vaccine can be approved by the FDA quickly compared to a traditional FDA-approval process, but that doesn’t mean it cuts corners when it comes to evaluating vaccine data, risks and benefits.

The Clinical Trial Process

The vaccine candidates were quick to begin testing in clinical trials on adult volunteers so they could gather data to support an EUA approval. Clinical trials are conducted in three phases

In a Phase 1 trial, the vaccine is given to a small number of healthy people — usually about 20 to 100. During this phase, researchers are hoping to learn if the vaccine is safe and if it seems to work. The volunteers who get the vaccine are monitored closely for side effects.

Phase 2 studies involve hundreds of volunteers. In this phase, the researchers are looking to understand how the vaccine is working in the volunteers’ immune system and which side effects are most common.

By Phase 3, the trial enlists thousands of people to learn more about how the vaccine works and how their immunity to the disease compares to those who have not received the vaccine. This stage is important for providing the information the FDA needs to approve the vaccine.

At any stage, if the vaccine doesn’t seem to be safe or effective, the FDA may stop the study from continuing.

How Do Vaccines Get FDA Approval?

After the three phases of clinical trials are complete, the vaccine manufacturer must present data to an FDA review team that proves the vaccine is safe and effective and that its benefits outweigh any risks.

Once a vaccine is approved, it must be properly labeled with its risks and benefits, as well as its correct use, so health care providers can share this information with their patients.

Before an approved vaccine can get distributed to the public, the manufacturer must test all batches of the vaccine, called lots, for safety, potency and purity. The FDA reviews this information before the lots can be released. The FDA also routinely inspects the facilities where the vaccines are produced to ensure the product’s safety and quality.

Are Vaccines Monitored for Safety?

Even after a vaccine gains approval and is licensed, its safety is closely monitored by the FDA and the Centers for Disease Control and Prevention (CDC). This helps identify any possible risks of the vaccine.

To help monitor vaccine safety, several reporting systems collect information about vaccine use:

  • Clinical Immunization Safety Assessment Project (CISA) is a partnership between the CDC and seven research centers; it helps health care providers answer complex questions about vaccine safety and conducts clinical studies around vaccine safety
  • Post-Licensure Rapid Immunization Safety Monitoring (PRISM) is a network of health care organizations from across the U.S. that analyzes the health care data of more than 190 million people
  • Vaccine Adverse Event Reporting System (VAERS) collects reports of adverse side effects from health care providers, parents and patients, and then analyzes the information for safety concerns
  • Vaccine Safety Datalink (VSD) is a network of health care organizations from across the U.S. that analyzes the health care records of more than 24 million people

If a vaccine is found to have a serious risk or side effect, the recommendations for its use may change.

How Do Vaccines Get Added to the Immunization Schedule?

Once a new vaccine is developed and is proven to be effective and safe, it may be added to to the schedule of recommended vaccines, like the flu vaccine and other vaccines that are recommended for kids and adults.

Overseeing this process is the Advisory Council on Immunization Practices (ACIP), a group of health experts who review clinical trials to develop a vaccine’s recommended use. The ACIP considers several factors before recommending a vaccine be added to the immunization schedule. These considerations include:

  • How many people would get the disease without the vaccine
  • How well the vaccine works at different ages
  • The safety of the vaccine in different age groups
  • The severity of the disease the vaccine prevents

Once the ACIP recommends a vaccine be added to the schedule, the director of the CDC must review and approve the recommendation before it can be listed on the U.S. childhood immunization schedule.

We’re Here for You and Your Family

Throughout the pandemic, we’re here to help you stay informed and feel empowered to care for yourself and your family. When it’s your turn to get the shot, encourage their shot.

Sign up for email alerts at and visit our Coronavirus Resource Hub for our latest tips and updates about staying safe from COVID-19.

Recent Blogs

A Woman Sits at a Table with a Cup of Tea Blowing Her Nose
Is It a Cold, the Flu, COVID-19 or Seasonal Allergies?
A Woman Checks the Results of an at Home COVID test.
Fall Wellness: Free COVID-19 Tests Are Back Again
The Eris Variant: What We Know About EG.5
A Woman Rides the Bus with Her Little Brother While Using Her Smartphone.
FDA Authorizes Moderna, Pfizer-BioNTech Bivalent COVID-19 Vaccine Boosters
COVID-19: Transitioning From Pandemic to Endemic
View More Articles