Approval of COVID-19 Vaccines Will Change Nature of Clinical Trials

Kenneth J. Terry, MA

November 26, 2020

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While stressing the urgent need to vaccinate the whole US population, infectious disease experts and medical ethicists are raising questions about the clinical trials needed to answer important questions about the new COVID-19 vaccines.

In a statement released on November 20, Barbara Alexander, MD, president of the Infectious Diseases Society of America (IDSA) and a professor at Duke University, Durham, North Carolina, commented on Pfizer and BioNTech's application to the US Food and Drug Administration (FDA) for an emergency use authorization (EUA) for its COVID-19 vaccine. Besides emphasizing the need for a transparent review of the companies' trial data prior to the FDA granting an EUA, she said, "If emergency use authorization is granted, clinical trials and data collection must continue."

In an interview with Medscape Medical News, Alexander said she is convinced that both Pfizer and Moderna, which is also expected to seek an EUA soon, will continue their clinical trials to monitor the long-term safety and efficacy of their vaccines.

"The EUA guidance for COVID vaccine authorization is very clear that clinical trials will move forward," she said. "Any EUA request would have to include a strategy to ensure that the long-term safety and efficacy of a vaccine could be monitored. I see no evidence that either Pfizer or Moderna is not prepared to follow those regulations."

Eventually, she added, the drugmakers will have to seek full FDA approval to replace an EUA, which as its name signifies, is designed for public health emergencies. "The EUA is a tool to help us get the vaccine into circulation and have it start working as quickly as possible in the current health crisis," she said. "But once the crisis is over, if the sponsor wants to continue to market their vaccine, they have to go forward and get full approval."

Medical ethicists, however, point out there may be ethical and practical dilemmas involved in continuing or initiating clinical trials once a vaccine has been approved for use even on an emergency basis.

In a commentary in the Annals of Internal Medicine, Rafael Dal-Re, MD, PhD, Arthur L. Caplan, PhD, and two other ethicists stipulated that the pandemic requires early licensing and deployment of COVID-19 vaccines. Nevertheless, they note, additional months of data are required to establish the long-term efficacy and safety of the vaccines. "Moreover, early deployment could interfere with the acquisition of long-term data," both on these vaccines and on others coming through the pipeline, they write.

In countries where an approved vaccine is deployed, the ethicists note, investigators must inform participants in an ongoing trial about the approved vaccine's status and ask if they want to continue in the study. If enough participants decline, the trial might have to be terminated early. At that point, researchers may not have sufficient long-term data to identify late-term safety issues, determine how long efficacy lasts, determine whether waning immunity is associated with reduced levels of antibodies, or identify the level of neutralizing antibodies that correlates with immunity.

Moreover, they observe, long-term trials are especially important for vaccines that use mRNA technology, because less is known about them than about traditional kinds of vaccines.

The authors also point out that early licensing of any vaccine might make it harder to evaluate vaccines that haven't yet been approved. "Once a vaccine is licensed, new placebo-controlled RCTs [randomized controlled trials] of other vaccines will not be acceptable ethically, and noninferiority RCTs will be the most likely alternative.

"The goal of noninferiority trials will be to demonstrate that the immune response (that is, neutralizing antibody titers or levels) of the candidate vaccine is not inferior to that of the approved vaccine within a prespecified margin, which the FDA has established as less than 10% for COVID-19 vaccines," the authors note. 

More Data With More Study Designs

Dial Hewlett, Jr, MD, medical director for disease control services, Westchester County Department of Health in White Plains, New York, told Medscape Medical News that the ethicists raise important issues that have been discussed in other forums, including a recent webinar of the National Academy of Medicine.

"As the authors point out, once you have a vaccine that has been shown to be effective and safe, it's no longer ethical to enroll people in placebo trials," he said.

Therefore, he said, Pfizer and Moderna will undoubtedly offer their vaccines to the people in their studies' placebo groups after the vaccines receive an EUA. Then they will follow everyone who has been vaccinated for 2 years to determine long-term safety. Efficacy will also continue to be measured as an adjunct of safety, he said.

With regard to the difficulty of reconsenting individuals to enter a new clinical trial after a vaccine has been approved, he said, "I'd agree that trying to get all the same participants to come into another study would be a challenge. You can, however, design studies that will allow you to obtain the same information. You will have a large number of people out there who haven't been vaccinated, and you can do single-arm longitudinal studies and measure a number of things in the individuals who are enrolled in those studies," he said.

"You can look at the immunologic markers, both antibody and T-cell. You can follow these individuals longitudinally to see if they do develop disease over a period of time. If they do, you can determine what their levels of response were," he added. "So there are opportunities to design studies that would give you some of the same information, although it would not be in the same population that was in the randomized trials."

For newer vaccines that have yet to be tested, he said, developers can compare "historical controls" from the trials of approved vaccines — ie, data from the unvaccinated participants in those studies — with the data from inoculating people with the novel agents. The historical data can be sex- and age-matched, among other things, to individuals in the new trials. Moreover, because the study protocols have been harmonized for all trials under Operation Warp Speed, it doesn't matter what kind of vaccine they're testing, he said.

It may be necessary to do additional studies to find out how long immunity lasts after people have been vaccinated, Hewlett pointed out.

"You may have a different trial design. You don't need a control arm to determine how long immunity lasts. You're just comparing the patients who were vaccinated to nothing," he said. "So you could have a single-arm trial on a group of people who consent to be immunized and followed. You can see what their antibody levels are and other surrogate markers, and you can see when they might develop disease, if they do. You'd need a large sample, but you can do that."

Hewlett also noted that additional studies will be required to determine whether the new vaccines stop transmission of the coronavirus or just prevent symptoms of COVID-19. Until it's established that a vaccine halts transmission or the country achieves herd immunity, he said, "we'll still have to wear masks and take other precautions, because a significant portion of people will still be at risk."

'A Lot of Redundancy'

Alexander emphasized that any safety or efficacy issues with the first COVID-19 vaccines must be identified before the vaccine is offered to a large portion of the US population.

"While the data from the Pfizer and Moderna trials are said to be favorable, we at IDSA want to make sure that whatever vaccine comes to market is safe," she said. "Having an unsafe vaccine on the market would be worse than no vaccine, because you're compromising the public confidence. We have to make sure the public trusts the process and that sufficient data have been evaluated to ensure the vaccine is safe and efficacious.

"I believe the FDA is being very careful and thoughtful in their response," Alexander said. "They realize how important it is to get a vaccine and save lives. While they're doing things differently and moving much faster than before, they're still trying to be thoughtful and reasonable. They don't seem to be putting people at risk or circumventing the regulatory standards."

Moreover, she pointed out, the FDA's Vaccines and Related Biological Products Advisory Committee, which is expected to meet on December 10, will review the trial data before the agency grants an EUA to Pfizer or Moderna. Then the FDA will post the data publicly.

The next step is for the Advisory Committee on Immunization Practices of the Centers for Disease Control and Prevention to look at the data and decide who in the United States should receive the vaccine first, she pointed out. And both Pfizer and Moderna have shown their data to advisory panels of outside experts.

"There's a lot of redundancy, and a lot of people are looking at the data," Alexander said. "So I don't think we're cutting corners to get it out there more quickly."

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