Approval versus Emergency Use Authorization (EUA): What’s the difference?

This article is an extended version of a story that originally aired in the May 3, 2021 issue of Oregon Coronavirus Update.

We’ve noticed that there’s been some confusion online about whether an Emergency Use Authorization (EUA) is the same as approval from the Food and Drug Administration (FDA).

Let’s get into it and start by looking at what the FDA does.


The U.S. Food and Drug Administration (FDA) is concerned with preserving the public health of the U.S. To meet this goal, the FDA regulates drugs, tobacco, biological products, medical devices, cosmetics, products that emit radiation and foods that are used in the U.S.

For the sake of this article, we’re going to focus on the FDA’s relationship with biological products, which include vaccines.

FDA Approval

Before a vaccine is used in the U.S., it must be carefully reviewed by the FDA.

The FDA reviews “the safety, efficacy, purity and potency” of every vaccine as demonstrated through rigorous testing, which usually begins with testing in animals.

If animals experience the intended effect of vaccination without significant side effects, then the testing will continue in human trials, which are carried out in three phases.

In the first phase, 20–100 healthy volunteers are vaccinated so that scientists can begin learning about the effects of the drug, including what side effects there might be, if any.

If the vaccine doesn’t appear to cause any serious side effects, testing moves to Phase 2, where hundreds of volunteers are tested in a similar fashion. In Phase 2, the optimal dose of the drug is determined.

If the vaccine continues to show promise, testing will move to Phase 3, where thousands of volunteers will be studied. Again, researchers will attempt to understand the true safety and efficacy of the vaccines and determine if there are any side effects.

If the clinical trials show sufficient safety and efficacy, the FDA will also evaluate the vaccine manufacturing processes in place to ensure that the vaccine can be made in a safe fashion on a consistent basis.

Following testing, FDA scientists and medical professionals carefully review all collected data and decide whether the vaccine is sufficiently safe and beneficial for use. If the vaccine meets these criteria, it receives FDA approval, which means that any provider licensed to do so may prescribe the vaccine — according to his or her clinical judgment — to anyone. After approval, vaccine safety monitoring will continue through the use of surveillance tools like the Vaccine Adverse Event Reporting System (VAERS), the Vaccine Safety Datalink, and the Biologics Effectiveness and Safety System.

Emergency Use Authorization

The COVID-19 vaccines from Pfizer, Moderna and Johnson & Johnson have all received an Emergency Use Authorization (EUA) from the FDA. EUAs may be granted only during a public health emergency and when there are no adequate, approved, and available alternatives.

While this isn’t the same as FDA approval, it doesn’t mean that these vaccines haven’t also undergone rigorous safety testing. Quite the opposite.

Similar to the FDA approval process, vaccine studies for EUA are conducted across three phases.

In the first phase, a small group of healthy people are vaccinated to determine the vaccine’s safety and effectiveness. If the vaccine doesn’t produce any harmful effects, it will move on to Phase 2.

In Phase 2, hundreds of people with more diverse backgrounds and varying health conditions are studied. Again, the vaccine will be studied to determine if any side effects arise, as well as how the size of the dose affects the vaccine’s safety and ability to produce an immune response.

If all goes well in Phase 2, the vaccine study will move onto Phase 3, where thousands of people from even more diverse backgrounds will be monitored.

Each COVID-19 vaccine currently authorized for emergency use in the U.S. was studied in numbers of people well above the typical standards:

  • The Pfizer vaccine was studied in a clinical trial of more than 43,000 participants.
  • The Moderna vaccine was studied in a clinical trial of more than 30,000 participants.
  • The Johnson & Johnson vaccine was studied in a clinical trial of more than 40,000 participants.

The data in these phase 3 trials are reviewed by an independent group (known as a “data safety monitoring board”), which can halt the study if it believes that the vaccine is proving to be harmful. If the phase 3 trials produce satisfactory results, the manufacturer can decide to apply to the FDA for EUA.

Once a vaccine manufacturer applies for EUA, FDA professionals — career scientists and physicians with expertise in vaccine research — scrutinize the data on the vaccine.

Simultaneously, the FDA convenes its Vaccines and Related Biological Products Advisory Committee (VRBPAC), which is made up of physicians, public health experts and scientists who have no affiliations or ties to any of the vaccines submitted for authorization. This committee conducts another independent review and submits its findings and recommendation to the FDA for consideration. Weighing all the evidence, as well as the independent reviews of the data, the FDA will then decide whether a vaccine should be authorized for emergency use. EUA specifies which groups may be vaccinated, and is valid only while the emergency exists.

In the case of vaccines that are either approved for use or that receive an EUA, the CDC convenes its Advisory Committee on Immunization Practices, which reviews the available data, along with epidemiologic data about the risk of the disease overall and in specific groups, and makes recommendations regarding who should get the vaccine. CDC typically adopts these recommendations and makes them available to physicians, public health agencies and the public.

The Pfizer, Moderna and Johnson & Johnson COVID-19 vaccines were all reviewed thoroughly before receiving EUAs and continue to be monitored through the Vaccine Adverse Event Reporting System (VAERS). In a review of the more than 145 million vaccine doses that had been administered by March 29, the CDC had determined that there were no safety problems with the COVID-19 vaccines.


FDA Approval and Emergency Use Authorization are two separate ways in which the FDA can make a vaccine available for use in the United States. Although an EUA is granted during a public health emergency, that does not mean that the vaccines that have been granted EUA haven’t undergone rigorous and comprehensive safety testing. Even now, after millions of Americans have been safely vaccinated, the COVID-19 vaccines continue to be monitored intensely through several vaccine surveillance systems to safeguard the well-being of every individual who chooses to get vaccinated.

To learn more about the COVID-19 vaccine situation in Oregon, visit our webpage (English or Spanish), which has a breakdown of distribution and other information.

Other Resources

  1. What is an EUA? – Youtube video from the FDA
  2. Emergency Use Authorization for Vaccines Explained
  3. Ensuring the Safety of Vaccines in the United States
  4. Understanding the Regulatory Terminology of Potential Preventions and Treatments for COVID-19
  5. CDC Safety of COVID-19 Vaccines