资源环境科技发展态势分析平台

Science’s COVID-19 reporting is supported by the Heising-Simons Foundation.

An ethics board that oversees clinical trials in the United Kingdom today said a research team there can begin to intentionally infect volunteers with the virus that causes COVID-19, a world-first experiment intended to accelerate research into vaccines against the disease.

The hotly debated “human challenge” experiment will, as a first step, determine the lowest level of the pandemic coronavirus, SARS-CoV-2, needed to infect the healthy, young volunteers. The researchers then plan to vaccinate additional volunteers and expose them to that “challenge dose” to assess protection and the immune responses that correlate with it.

The human challenge model, long used for flu and several other infectious diseases, allows rapid comparisons of different vaccines and provides a simpler way to determine why they work or fail than the large-scale efficacy trials underway. The unavoidable risk of COVID-19 challenge trials, however, is that the disease can be fatal, even in healthy, young people, and there is no proven “rescue” drug, a treatment that reliably stops a SARS-CoV-2 infection in its tracks. Opponents also note that even a mild SARS-CoV-2 infection can have long-term consequences and say the questions that human challenges address can also be answered through conventional vaccine trials.

Still, many people in the United Kingdom and elsewhere have declared their willingness to participate in such studies. And scientists have said that despite the success of multiple COVID-19 vaccines in recent months, the trials could offer vital information.

The U.K. team that won permission today to move forward will select 90 healthy volunteers between 18 and 30 years old and, after exposing them to varying amounts of SARS-CoV-2, will isolate and monitor them 24 hours a day. People who become infected will quickly be offered remdesivir, a drug approved in several countries to treat infected people who are at high risk of severe COVID-19 or who are already hospitalized with the disease, says the trial’s principal investigator, immunologist Christopher Chiu of Imperial College London. “We will be taking twice-daily viral load measurements so we may well be able to see if remdesivir has efficacy as a very early pre-emptive treatment.”

Remdesivir has only been tested in hospitalized patients, with mixed results, but its discoverers have long contended it will work better if given to people earlier in an infection. Yet even if remdesivir prevents disease in these volunteers, giving the drug to newly infected people is not likely to be practical on a large scale because it must be infused, it’s relatively expensive, and most people will have mild symptoms or none at all without treatment.

Human challenge trials could be used to study vaccines that have been tweaked to be more effective against recently emerged SARS-CoV-2 variants that transmit more readily, dodge the immune response, or do both. But the initial U.K. study will use an isolate of the virus obtained in summer 2020, before the most concerning new strains surfaced. “We are currently considering which variants to pursue next so that they are most relevant for testing of re-engineered vaccines,” Chiu says.