An EUA, or Emergency Use Authorization, is a mechanism that allows the U.S. Food and Drug Administration to make medical products available during a public health emergency before they go through the full approval process. It applies to drugs, vaccines, diagnostic tests, and medical devices that address serious or life-threatening conditions caused by chemical, biological, radiological, or nuclear threats, including infectious diseases. The concept became widely known during the COVID-19 pandemic, but the authority has existed since 2004.
How an EUA Gets Triggered
The FDA cannot issue an EUA on its own. First, the Secretary of Health and Human Services must formally declare that circumstances justify emergency authorization. That declaration must be based on a determination of a threat or potential threat made by the Secretary of HHS, the Secretary of Homeland Security, or the Secretary of Defense. Only after this declaration is in place can the FDA begin authorizing specific products.
Several criteria must be met. The disease or condition must be serious or life-threatening. There must be reason to believe the product may be effective. And critically, there must be no adequate, approved, and available alternatives already on the market. This last requirement means EUAs typically fill a gap where no existing treatment or diagnostic tool can do the job.
The Evidence Standard Is Lower Than Full Approval
This is the distinction that generated the most public debate during COVID-19. For full FDA approval, a manufacturer must establish that a product is “safe and effective” through substantial evidence from adequate, well-controlled clinical trials. For an EUA, the FDA only needs to determine that it is “reasonable to believe” the product “may be effective” based on the totality of available scientific evidence. That evidence does not need to include completed clinical trials.
The FDA has openly acknowledged this difference in its own guidance documents. The “may be effective” threshold is deliberately lower because the whole point of an EUA is speed during a crisis. The tradeoff is that some uncertainty remains about benefits and risks at the time of authorization, which is why EUAs come with specific conditions and disclosure requirements.
What Products Can Receive an EUA
EUAs cover three broad categories: therapeutics (drugs and biologics like vaccines), medical devices (ventilators, respirators, protective equipment), and diagnostic tests. During COVID-19, all three categories saw extensive use. Hundreds of diagnostic tests were authorized under EUA to rapidly expand testing capacity, while vaccines and treatments followed.
The regulatory bar differs somewhat across these categories even under normal circumstances. Devices rarely require clinical trials for standard approval, while drugs and biologics typically do. Under an EUA, the flexibility increases further, allowing products to reach the public in weeks or months rather than years.
History Before COVID-19
The EUA authority grew out of post-9/11 bioterrorism fears. After the September 11 attacks and the anthrax mail attacks that followed, Congress passed the Project Bioshield Act of 2004, which created the legal framework for emergency authorization. The original focus was on bioterror threats, not naturally occurring pandemics.
For the first 16 years, the authority was used sparingly. Its most extensive pre-COVID use came during the 2009 H1N1 swine flu pandemic, when the FDA authorized medical equipment and existing flu drugs. It was also used preemptively for threats like MERS, Ebola, and Zika, though none of those outbreaks materialized significantly in the United States. Before COVID-19, the only vaccine to ever receive an EUA was an anthrax vaccine in 2005, and that product had already been formally approved for other purposes.
Safety Monitoring Under an EUA
EUA products are not unmonitored. Each authorization includes specific Conditions of Authorization that spell out adverse event reporting requirements. For medical devices, manufacturers generally must report deaths, serious injuries, and malfunctions to the FDA within 30 calendar days of learning about them, or within 5 days if the event requires immediate action to prevent substantial harm to the public.
The key difference from fully approved products is not that monitoring is absent but that it is happening in real time alongside widespread public use, rather than being largely completed before the product reaches the market.
What You’re Told Before Receiving an EUA Product
Federal law requires that anyone offered an EUA product receives specific information beforehand. You must be told that the product is authorized for emergency use (not fully approved), what the significant known and potential benefits and risks are, the extent to which those benefits and risks are still unknown, and that you have the option to accept or refuse the product. You must also be informed of any available alternatives and their risks and benefits.
This information is delivered through a standardized “Fact Sheet for Recipients” that accompanies every EUA product. It includes a description of the disease, what to discuss with a healthcare provider, how to report side effects, and dosing instructions if applicable.
What Happens When the Emergency Ends
An EUA is temporary by design. If the HHS Secretary terminates the emergency declaration that supports it, all EUAs issued under that declaration cease to be effective. Before termination, the government must publish advance notice in the Federal Register and allow a reasonable transition period so manufacturers, healthcare facilities, and patients can adjust.
For products that have not achieved full approval by that point, the transition period allows for proper disposition of remaining stock and associated labeling. There is one important exception: if a patient was already receiving an unapproved product while the EUA was active, their physician can continue administering it if medically necessary, even after the authorization ends.
Products can also transition from EUA to full approval while the emergency is still active. This is what happened with several COVID-19 vaccines, which received full FDA approval after completing the standard review process while remaining available under EUA during the interim. As of late 2024, some COVID-19 vaccines still operate under EUA for certain age groups or formulations, including the Novavax COVID-19 vaccine for individuals 12 and older.
EUA vs. Full Approval in Practice
The practical difference for most people comes down to the level of certainty. A fully approved product has been proven safe and effective through rigorous, completed trials. An EUA product has enough evidence to suggest it may be effective, with a favorable risk-benefit profile given the severity of the emergency. Both undergo FDA review. Both require ongoing safety reporting. But the depth and duration of that review differ substantially.
An EUA can also be revoked at any time if circumstances change: if the justifying emergency no longer exists, if the product no longer meets the criteria for authorization, or if new information makes revocation appropriate for public safety. This built-in flexibility is part of what makes the system function during rapidly evolving threats.