The Emergency Use Authorization of Pharmaceuticals: History and Utility During the COVID-19 Pandemic

Development of therapies and preventative vaccines to attenuate the often-devastating impact of the global COVID-19 pandemic have been at the daily forefront of both lay press and medical literature. While the basic public health hygienic measures were the foundation of efforts to ease the spread of infection and its burden, there was also great attention to innovative developments in pharmaceutical medicine.

The pharmaceutical focus during the pandemic was on developing vaccines to protect individual patients and to foster herd immunity and therapies to treat the severe manifestations of disease. With respect to the latter, these developments included both novel therapeutics and, more often, the repurposing of drugs with known safety and efficacy in other indications (e.g., malaria) based on a working hypothesis of potential benefit against COVID-19. In both cases, the Emergency Use Authorization (EUA) served as a regulatory vehicle to allow patient use prior to formal New Drug Application (NDA) submissions. In the first year of the pandemic, we witnessed many approvals of EUAs; but also, amendments and withdrawals as the quickly evolving science drove decision making.

We provide a historical summary of the EUA, including its conception and its application during the first year of the pandemic. We then describe how the EUA program operated to provide safe and effective emergency relief from a devastating pandemic with prescription therapeutics and the early availability of vaccines. While diagnostics were the most common medical product that received an EUA from the FDA, we focus exclusively on the use of EUAs for therapeutic interventions aimed at counteracting or preventing COVID-19 infections.

2.1 Bioterrorism Threats Prompt EUA

After the 2001 anthrax bioterrorist attacks, the Project BioShield Act was enacted in 2004 to accelerate and bolster national security against potential bioterrorist attacks [1]. This legislation established the EUA under Section 564 of the Federal Food, Drug, and Cosmetic Act (FD&C Act), which permitted the emergency use of unapproved countermeasures against chemical, biological, radiological, or nuclear (CBRN) agent(s), among other authorities, when there are no adequate, approved, and available alternatives [2]. To enhance the flexibility of authorizations made under additional emergency circumstances, Section 564 of the FD&C Act was further amended by the Pandemic and All-Hazards Preparedness Reauthorization Act of 2013 (PAHPRA), the 21st Century Cures Act of 2016, and Public Law 115-92 of 2017 [2].

The purpose of an EUA is to allow for the use of unapproved medical countermeasures (MCMs) to diagnose, treat, or prevent serious or life-threatening disease or condition in response to a public health, military, and domestic emergency [3]. If the determinations needed to support an EUA declaration in the USA is met, this will enable the Secretary of Homeland Security, Secretary of Defense, Secretary of Department of Health and Human Services (HHS) to declare that circumstances exist to support an authorization [3]. Given that a MCM is considered for EUA for treatment of serious or life-threatening consequences, the FDA will evaluate the evidence of potential effectiveness of the MCM, i.e., whether it may be effective, as well as the associated risk-benefit profile, allowing that there are no adequate, approved, and available alternative options [3]. There were several public statements and media broadcasts that brought a particular drug or agent into the spotlight, which have ultimately turned our attention to the FDA, and to its decision-making process that has led to an EUA issuance. Since the inception of the EUA, the first authorization for a vaccine was for the Anthrax Vaccine Adsorbed (AVA) used by the Armed Forced [4] (Table 1).

2.2 HIV Infection and Expanded Access

The concept behind the EUA dates back to the decade after the first reported cases of human immunodeficiency virus and acquired immunodeficiency syndrome (HIV/AIDS) in 1981 [5]. Because of the urgent need for additional treatments, the United States Public Health Service (USPHS) created a "parallel track" expanded access program for an investigational drug known as dideoxyinosine (ddI) for AIDS patients with no other alternatives [5]. Notably, this pathway allowed eligible AIDS patients to access ddI while clinical trials of the drug were still ongoing. The fundamental principles of the parallel track/expanded access program formed the basis of the "accelerated approval (AA)" program, which was launched in 1992 [5]. Through the AA mechanism, the FDA was able to grant faster approval of new drugs that treat serious or life-threatening conditions based on a surrogate endpoint that is “reasonably likely” to predict clinical benefit [6], often well before clinical data supporting that benefit could be available. After granting an AA, confirmatory trials are required to verify its clinical effectiveness and benefit to support the AA [7]. The intentions of the EUA were reflected in the 1981 expanded access of ddI for AIDS patients.

2.3 EUA in Previous Pandemics

Apart from the significant role that EUAs played in authorizing the emergency use of treatments for 2009 H1N1 and COVID-19 vaccines [4, 8] (Tables 1, 2), other medical products (not shown here) including diagnostics, personal protective equipment (PPE), and medical devices have been authorized to combat the Zika virus, H7N9 virus, MERS-CoV, and Ebola virus [4]. Collectively, these events mark the historical successes that prove the utility of EUAs during times of public health emergencies, supporting its value as a regulatory tool.

3.1 Repurposing Existing Drugs for COVID-19

A drug developed for one therapeutic indication can sometimes be found beneficial in selected situations for a different disease or condition. In fact, the first effective antiviral drug was being developed for cancer when insightful thinking led researchers to explore its antiviral activity [9]. This led to the development of acyclovir, an antiviral medication commonly used to treat human herpes infection, creating a new era in antiviral research, and leading to a Nobel Prize for Gertrude Elion and two other pharmaceutical industry colleagues [10].

Existing drugs repurposed for COVID-19 infection have been reviewed by Farne et al. [11] and classified into (1) antivirals, (2) promotors of innate antiviral response and (3) immunomodulatory/anti-inflammatory drugs. Drugs within these categories have reasonable likelihood of potential benefit, but the dose, dosing regimen, and precautions were not established for treatment of COVID-19 infections. The pathway to rapidly bridge these hypotheses to patient benefit is not straightforward. Early in the pandemic, two drugs in particular were hypothesized to have therapeutic potential and were frequently discussed in the media. Hydroxychloroquine and remdesivir were supported by reasonable therapeutic hypothesis and were seen as an immediate option while awaiting the discovery and development of a vaccine. While many took comfort in the fact that the drugs had a defined therapeutic window for the conditions they were originally developed to treat, we came to appreciate the intricacies of therapeutics in the often-overlooked efforts that go into defining a clear indication for the drug, its dose and dosing regimen, its safety and needed precautions and its contraindications—all the basic elements of a drug product label (i.e., package insert).

The authority to use unapproved drugs for COVID-19 came to light as the pandemic was unfolding. On February 4, 2020, the U.S Department of Health and Human Services (HSS) declared a public health emergency that supported an EUA. This allowed the FDA to approve unapproved medical product(s) to be used in an emergency to diagnose, treat, or prevent COVID-19 infection, a life-threatening disease.

3.2 Hydroxychloroquine

On March 28, 2020, the FDA issued an EUA for oral formulations of chloroquine phosphate and hydroxychloroquine sulfate [12]. Hydroxychloroquine, despite demonstrating antiviral effects in laboratory models [13], ultimately did not show an acceptable benefit-risk relationship for the use to treat COVID-19 infection in humans [14]. As clinical trial data emerged, the agency concluded the drug may not be effective for COVID-19 infection and that any potential benefit did not outweigh its known and potential side effects and the EUA was revoked on June 15, 2020 [15] (Table 3). Chloroquine’s EUA did not last long. In addition to chloroquine phosphate and hydroxychloroquine sulfate, there were a number of other therapies and diagnostics that had their EUA revoked during the COVID-19 pandemic (Table 4).

Hydroxychloroquine’s failure to show meaningful benefit became more critical when serious safety issues emerged. The FDA announced reports of serious arrythmias in patients with COVID-19 treated with hydroxychloroquine or chloroquine, often in combination with azithromycin and other QT prolonging medicines [16]. The FDA also noted their concern for public health as they observed increase outpatient prescriptions, possibly indicating increased requests for prescriptions to physicians by patients. The public was able to witness firsthand the two ends of a therapeutic index (benefit and risk) and the importance of each in therapeutic decisions.

The hope of repurposing hydroxychloroquine had faded despite misguided enthusiasm by some influencers including country presidents and even a physician who used sermons as a minister to foster misinformation [17].

3.3 Remdesivir

The FDA issued an EUA for remdesivir in hospitalized patients with severe disease from COVID-19 infection on May 1, 2020 [18] (Tables 2, 3). Use for the treatment of suspected or laboratory-confirmed COVID-19 in adults and children hospitalized with severe disease was expanded on August 28, 2020 [19], and was FDA approved on October 22, 2020 [20]. Although remdesivir was being developed primarily against Ebola, like hydroxychloroquine, it showed an effect against coronaviruses in laboratory models [21, 22]. A clinical study demonstrated that remdesivir use was not associated with an overall difference in time to clinical improvement. In patients with symptoms for 10 days or less, faster time to clinical improvement, compared to placebo, was observed but the difference was not statistically significant [23].

In addition to conducting the trial noted above, the remdesivir manufacturer began accepting physician requests for compassionate use. With safety data for some 500 patients in the Ebola program [24, 25], a reasonable hypothesis for benefit, and no other therapy available, a compassionate use program was initiated. The investigators were able to observe clinical improvement in 68% of patients and nobody experienced side effects [26]. Compassionate use was followed by reporting of the ACTT-1 Trial where remdesivir demonstrated superiority to placebo based on a shortened time to recovery in hospitalized adults with COVID-19 and evidence of lower respiratory tract infection [27]. These data led to the drug’s authorization in the USA, EU, and UK. However, some uncertainty concerning the drug’s ultimate utility arose from the WHO 12,000 Patient Solidarity Trial [28], where no effect on survival was observed.

The lack of any alternative therapy at this phase of the pandemic reinforced the need to continue remdesivir clinical development and allow compassionate use in the interim. Ultimately, enough evidence became available for FDA NDA approval [29].

3.4 Antibody Therapies and Convalescent Plasma

Subsequent to the frequent public discussion on hydroxychloroquine and remdesivir, this was followed by EUAs for antibody therapy with convalescent plasma for the treatment of hospitalized patients with COVID-19 [30] (Tables 2, 3). This was proceeded by EUAs for antibody therapy with bamlanivimab [31] as well as casirivimab and imdevimab [32] co-administration (Table 2).

An important public health component is accurate and truthful communication of drug effects to the public in order to build trust in the regulatory processes. In the case of plasma administration, the FDA commissioner overstated the efficacy of therapy to the public, misinformation that was criticized by other health experts [33]. The commissioner’s prompt admission that the data could have been better represented helped reinforce trust, an element that subsequently came to the forefront in optimizing vaccine roll out.

The most celebrated use of EUAs came in mid-December 2020, with approvals for the Pfizer-BioNTech vaccine [34] followed a week later by ModernaTX’s application [35], with the first administration of both occurring days later. Nearing the end of February 2021, the third EUA was issued for the Janssen’s (Johnson & Johnson [J&J]) single-dose vaccine [36] (Table 1). Thus, within a year of declaring a global pandemic, three vaccines using two platforms (mRNA and viral vector-based) were authorized for emergency use in the USA.

Basic pharmacovigilance led to interrupted authorization for the Janssen’s viral vector vaccine. On April 13, the FDA and the Centers for Disease Control and Prevention (CDC) recommended a pause on the use of J&J’s vaccine after 6 reported cases of blood clots following vaccination [37,38,39]. After several days of data evaluation, the authorization was reinstituted with a warning on the low-risk association of vaccine-induced thrombotic thrombocytopenia (VITT) with the vaccine [40]. During this pause period, physicians became alerted to the type of clotting and appropriate therapy.

AstraZeneca’s viral vector vaccine was authorized in Europe and elsewhere in early 2021 but has not yet been granted an EUA by the FDA. Concerns about robustness of Phase 3 trial data are probably related to lagging US approval and the need for additional data [41].

During the early stages of the pandemic, the FDA has guided the pharmaceutical industry to facilitate the satisfaction of scientific and regulatory requirements for the development and licensure, and EUA issuance of COVID-19 vaccines [42, 43]. Once vaccine manufacturers complete a primary efficacy endpoint analysis in Phase 3 clinical trials that achieved the pre-specified success criteria of efficacy, an EUA application can be submitted to the FDA for review [43]. The FDA reviews data independent from the sponsor and can utilize an advisory committee of expert scientists and physicians from the Vaccines and Related Biological Products Advisory Committee (VRBPAC) [43]. This Committee deliberates on data in a public forum and votes on answers to questions provided by the FDA. While FDA is not bound by their recommendations, they usually follow them.

Robust pharmacovigilance follows EUA authorization, as demonstrated by the J&J case [37]. Full review of an NDA/BLA will generally follow an EUA, which, in the case of vaccines, will include follow-up observations as defined by the Phase 3 protocol and evaluated in ‘real world’ studies of various designs. It is worthy to note that some COVID-19 vaccines are now progressing to full NDAs as their EUA will expire once the declared emergency is over. More recently, on August 23, 2021, the FDA approved Pfizer's COVID-19 vaccine for individuals 16 years or older [44].

The approval of ddI for the treatment of AIDS was the first accelerated mechanism to bring lifesaving drugs to patients with no available alternatives [5]. Over a decade later, the origin of the EUA introduced the emergency use of the AVA to facilitate anthrax vaccine immunization of US military personnel with an increased risk of anthrax attacks [45]. These events along with the earlier pandemics, led to the use of EUAs, which have further supported and confirmed its utility during early public health emergencies.

In the COVID-19 pandemic, EUA vaccines were a remarkable accomplishment that was critical to mitigating the pandemic’s negative effects. The temporary pause in one authorization reflected a system that was active and effective [37]. EUAs of therapeutics were also critical, as was the dynamic nature of their intention where we witnessed expansions of use, withdrawal of use, and progression to approved NDAs.

While our review focused on the USA, other jurisdictions used similar processes to expedite safe and effective authorization of vaccinations given the unmet needs posed by the COVID-19 pandemic. There are, however, noteworthy differences. In the USA, three vaccines are currently authorized for emergency use, which does not include the AstraZeneca product. This product was granted conditional marketing authorization by the European Medicines Agency (EMA), also a fast-track authorization procedure to speed up approval of treatments and vaccines during public health emergencies [46]. Similarly, a Marketing Authorization with Conditions was granted by Health Canada. Information on what additional data may have been requested by FDA and whether AstraZeneca will submit for an EUA, or full BLA, or no authorization or approval in the USA remains unclear [47].

Another distinction of the EUA review process in the USA is the independent advisory committee proceedings being open to the public [48]. While EMA and Health Canada strive for transparency in data access [49], the ability to witness the debates and rationale of opinions of independent experts is most transparent and informative, a model that should be considered by other authorities.

Finally, the process in the USA resulted in authorization based on the product label, which was informed by findings of robust clinical trial. In Canada, for example, vaccine procurement issues early on, forced authorities to make recommendations away from the product monograph. Specifically, the dosing intervals in the two-dose vaccines were allowed to be broadened [50]. This was followed by non-regulator recommendations allowing two-dose vaccine products to be mixed. Advisories then suggested limited use of the AstraZeneca vaccine [51]. Both of these practices were not studied in the pivotal trials driving the authorization, thus ‘uncoupling’ the data from these controlled studies, including long-term safety. While the ultimate benefit-risk of these debatable practices is unknown [52], it is noteworthy in the context of EUAs granted in the USA that ultimate dosing and administration did not stray from the data submitted by the sponsor and assessed by the FDA.

The EUA, originally designed to provide rapid antidotes for potential bioterrorism, acted as a critical regulatory pathway for vaccines and therapeutics throughout the COVID-19 pandemic. Our experiences demonstrated the dynamic nature of the scientific review process where some products had their emergency use expanded, some withdrawn after evaluation of new data, and some moving on to full NDA approval. The EUA was a critical component in counteracting the pandemic through pharmaceutical medicine and proved a remarkable framework for the monumental drug development achievements. This experience will inform regulatory processes in future pandemics and public health crises.