Human challenge trials could help test covid-19 vaccines
Researchers in the UK have announced plans to infect volunteers with the coronavirus, starting in January. The initial aim will be to establish the minimum infectious dose before testing potential vaccines. The study will be funded by the UK government, but has yet to get final ethical approval.
“The top priority is participants’ safety,” says Chris Chiu at Imperial College London, whose team will carry out the study. “We have spent many months thinking about the evidence and weighing up the pros and cons.”
The coronavirus doses will be created by a company called hVIVO, as the research requires a pure, quantifiable source of the virus, rather than an infection spreading person to person. The doses will contain the same strain that is currently circulating and not weakened, or attenuated, in any way.
Volunteers will have the virus delivered to their nose in droplets, a method widely used in previous studies of this kind. As soon they show signs of infection, they will be given the antiviral drug remdesivir.
A large trial recently found that remdesivir didn’t reduce the death rate from covid-19. However, that trial involved severely ill people who had already been hospitalised, says Chiu. He thinks giving the drug very early on will stop the infection spreading to the lungs. The team will also consider using other drugs such as antibodies as more evidence becomes available.
The volunteers will be healthy individuals aged between 18 and 30. Initially they are likely to be from a white ethnic background because of evidence that black, Asian and minority ethnic people are more likely to get severely ill. However, the team says it will include volunteers from more diverse backgrounds as soon as it can do so safely.
The study will be done at the Royal Free Hospital in London. If any volunteers do become severely ill, the study will be paused to assess whether it is safe to continue. However, the team’s expectation is that most volunteers won’t even develop any symptoms.
Even if there are no adverse events, this first phase could still take several months if the initial doses prove to be too low, Chiu says. That’s because there are only a limited number of beds available, and volunteers will have to remain quarantined for weeks even if they don’t become infected.
This means it could be many months yet before the team can start testing potential vaccines by trying to infect volunteers who have been given a vaccine – known as human challenge trials – by which time one or more vaccines might already be available through conventional testing. “We are likely to see the results of phase III trials in the next few months,” says Peter Openshaw at Imperial College London.
However, many different vaccines will be developed over the next three or four years, says Openshaw, and being able to do human challenge trials will be a very valuable way of comparing them.
“This will be a way to much more rapidly compare the efficacy and safety of vaccines,” says Robert Read at the University of Southampton, UK.
Challenge studies of this kind won’t reveal if vaccines protect the oldest and most vulnerable people, but they can speed up progress by revealing which potential vaccines have no chance of working, says Andrew Catchpole, chief scientist at hVIVO. “What it can do is fast-track vaccines for those groups,” he says.
The team will set up a website where people can register their interest in taking part while the study awaits approval from the UK’s Medicines and Healthcare Products Regulatory Agency and the Health Research Authority. Volunteers will be compensated for their time, but Chiu declined to say how much money they will receive.
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