Human challenge trials bring a vaccine a step closer


Volunteering to be infected with a virus that can be deadly and has no sure-fire cure takes a particular kind of courage. Yet in pursuit of an inoculation against coronavirus, the world’s first Covid-19 human challenge trials — with healthy patients being infected to assess the effectiveness of experimental vaccines — are set to be announced by the UK next week. If the ethical and technical issues can be addressed in time, trials will start in January at a quarantine facility in London.

Such trials, and the ethical dilemmas they present, are a global issue. Similar preparations are under way in the US, where the National Institutes of Health has awarded contracts to support the manufacturing of coronavirus strains suitable for challenge studies, and parts of Europe.

With further waves of coronavirus triggering renewed restrictions in countries such as Spain, France and the UK, and cases mushrooming in Latin America, India and elsewhere, vaccines still offer the best hope of deliverance. A fully effective treatment remains elusive, while the technology and capacity for mass, regular testing that could make it easier to live with the virus remain some way off.

Proponents of challenge trials argue they are the best way to narrow the large field of promising Covid-19 vaccine candidates that are likely to move into large-scale clinical testing next year. Ten vaccines are already in phase 3 trials, each requiring around 30,000 volunteers to be inoculated. Participants in those trials then go about their normal lives in the community and the researchers see how many develop Covid-19 — and how serious the symptoms are — compared with a control group who receive a placebo jab.

It will be hard to find enough volunteers and clinical resources to carry out conventional trials on that scale for the dozens of potential vaccines that will be ready for clinical testing in 2021. Challenge trials short-circuit the process. Volunteers receive the vaccine and about a month later a dose of coronavirus under controlled conditions, isolated in a quarantine facility where their health and immune responses are monitored carefully. Typically a participant would spend about a month in the clinic and (in the UK) receive a payment in the region of £4,000 to £5,000.

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Though challenge trials have been around for 200 years, what makes coronavirus different from most recent instances is the lack of a certain treatment for participants who fall ill. Subjects are likely to be young and low-risk. But each trial will need regulators and an independent ethics committee to be satisfied that consenting volunteers have been given all possible information on the risks. Regulators will need to ensure too that the virus strain is as mild as possible yet sufficient to provoke an immune response, doses given are as low as possible to achieve infection, and there is an established “rescue routine” for anyone who becomes sick. The UK trial will use the antiviral drug remdesivir.

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Without infection challenge studies it may also be impossible to compare the efficacy of all Covid-19 vaccine candidates. Early successes should not crowd out vaccines that take longer to develop but work better or more safely.

Governments must ensure challenge trials are run with full transparency, so as not to undermine the (already fragile) public trust in Covid-19 vaccines. But conversely, if such trials can demonstrate some vaccines are effective while being carried out responsibly and ethically, they may help to reassure a nervous public and counter the efforts of anti-vaccine campaigners. The courageous volunteers will certainly deserve our gratitude.



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