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Faster vaccine trials could save lives without sacrificing ethics

The UK leads the way on human challenge trials.

A nurse in London prepares a COVID-19 vaccine to administer to a volunteer.
A nurse in London prepares a COVID-19 vaccine to administer to a volunteer.Kirsty Wigglesworth/Associated Press

A group of healthy young adults in the United Kingdom have just been infected with COVID-19. They didn’t catch the virus at a crowded pub or a college party. They were infected with it on purpose — in the name of science.

This is known as a human challenge trial, and it’s the first such trial for COVID-19 approved anywhere in the world. Researchers hope that by exposing 90 volunteers between the ages of 18 and 30 to the virus, they’ll discover the smallest amount of exposure necessary to cause an infection and gauge how the immune system mounts its initial defense. Those are difficult questions to answer through conventional trials, in which researchers vaccinate people and then wait months for the subjects to be exposed to the virus as they go about their normal lives.


Since the onset of the COVID-19 pandemic, public health experts have debated whether to allow challenge trials to go forward. The benefits could be substantial: Though vaccines developed through conventional trials have already been approved, challenge trials could accelerate the development of more effective treatments and second-generation vaccines, potentially saving lives — especially with new variants appearing all the time. The advocacy group 1Day Sooner has gathered the names of more than 38,000 people in 166 countries who said they’d be eager to volunteer, and last July, the group published an open letter, signed by dozens of influential philosophers and scientists, including 15 Nobel Prize winners, calling for human challenge trials in the United States.

Others are wary. Critics argue that it’s unethical to infect healthy people with a virus that could lead to severe illness, long-term disability, and even death. Although scientists have used challenge trials for diseases such as malaria and influenza, COVID-19 differs in that there is currently no reliable treatment. And experimental results from a study of healthy young people may not generalize to more vulnerable populations.


But these valid concerns are far outweighed by the potential benefits.

Moderna had designed its vaccine candidate by Jan. 13, 2020, just two days after the virus’s genetic sequence was released. It had already manufactured the vaccine before the first American death. If a challenge trial had even marginally sped up the testing and approval process and thus gotten vaccines to the public sooner, it might have averted many thousands of deaths. To be sure, the conventional trials for Pfizer and Moderna’s vaccines went relatively rapidly, but they generated sufficient data only because the virus was so prevalent that there was a sizable chance of infections among trial participants who had received placebos. That’s one way to demonstrate the vaccines’ efficacy, but if scientists had run a challenge trial early in the outbreak, they could have gotten good data about the vaccines in a controlled environment rather than needing the virus to be rampant everywhere. And speeding vaccine approval could have greatly increased the overall suppression of the virus.

As for the ethical concerns, we regularly ask people to incur personal risks for the greater good — think of soldiers or firefighters jeopardizing their lives in the line of duty, not to mention nurses and doctors during the pandemic. And although it’s true that the current trial is being conducted on young and healthy people, follow-up studies could confirm a vaccine’s efficacy in other populations.


One final concern that skeptics have raised is that the public will view these trials as unethical, feeding distrust and delaying uptake.

Fortunately, new research suggests this concern is unfounded. In a paper published this January, a team of political scientists, bioethicists, and public health researchers surveyed a representative sample of nearly 2,200 people in the United States, as well as around 500 people in each of seven other locations: Australia, Canada, Hong Kong, New Zealand, Singapore, South Africa, and the United Kingdom. The researchers explained how challenge trials differ from standard trials and asked the participants what they thought about the ethics.

They found staggering support for challenge trials in every location. Three-quarters of respondents preferred them to standard Phase 3 trials — and among those who seemed to thoroughly understand how the trials worked, nearly 90 percent preferred them to the standard trials. In the United States, there were similar levels of support among Democrats, Republicans, and independents, as well as among vulnerable groups, like those over 65, essential workers, and racial minorities. Every demographic group thought challenge trials were more ethical and more scientifically valid — and, perhaps most important, expressed greater willingness to take a vaccine if it had been tested in a challenge trial. Sometimes, the public’s views surprise the experts.

Given the widespread support for these trials, as well as their potential benefits, countries around the world should follow the United Kingdom’s lead. Challenge trials could save lives now — and they just might halt the next pandemic.


Bryan Schonfeld and Sam Winter-Levy are PhD candidates in politics at Princeton University.