Scientists have warned there could be major delays in producing a Covid-19 vaccine if current UK infection rates remain low and lengthy waiting times are needed to show if candidate products are working. As a result, some researchers insist that ministers must now consider implementing radical alternative measures to speed up vaccine development.

In particular, they argue that Britain should consider deliberately infecting volunteers involved in vaccine-testing projects – in line with World Health Organization proposals to set up such human challenge trials. Earlier this month, the WHO issued a 19-page set of guidelines on how these trials might operate.

However, other UK scientists have reacted with horror at the proposal to implement human challenge trials for a Covid-19 vaccine on the grounds that these could cause serious illness and possibly deaths of volunteers who had been deliberately infected with the virus.

The dilemma was summed up by Jonathan Ives of the Centre for Ethics in Medicine at Bristol University. “If we were to do this, we would be asking healthy people to put their wellbeing and their lives at risk for the good of society at large. On the other hand, taking that risk could speed up vaccine development and save many, many lives. So I think there could be grounds for going ahead with challenge trials, though it would be based on a very finely balanced argument.”

Figures released last week suggest about 7% of the UK population may have already been infected with Covid-19 virus, a relatively low level of infection that poses problems for testing vaccines. A sufficient number of volunteers has to be exposed to the virus to see if a vaccine protects them or not. But if their chances of being in contact with an infected person are low, it will take a long time to demonstrate the efficacy of a vaccine candidate.

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As a result, scientists have proposed that human challenge trials could be introduced to test a vaccine quickly and so save thousands of lives by preventing future infections. “Levels of infection in the community are already low, and if this virus behaves like other respiratory diseases and coronaviruses, there may be even lower levels over the summer,” said Professor Lawrence Young of Warwick University Medical School. “There will not be enough people secreting the virus to be in contact with volunteers in vaccine projects. It is just not going to work.”

Young argues that human challenge trials should be considered “very seriously” for the UK. These would involve giving volunteers either a placebo or a vaccine, as is normally done in trials. But instead of waiting to find out how the two groups fare without interference, scientists would deliberately infect them with the Covid-19 virus. This would very quickly show if a vaccine works or not.

“Only very healthy young people – around the age of 25 – who have given informed consent would be used,” added Young, who points out that such trials have already been used to test the efficacy of vaccines for flu and the common cold.

However, these ailments pose relatively low risks to volunteers. Covid-19 can have serious side-effects, mainly for the elderly but also in a few rare cases of young, apparently healthy people. This point is acknowledged by Young. “Before we went ahead with challenge trials, we would need to have developed some very effective therapy – an anti-viral drug perhaps – that could be used in the few cases where something went seriously wrong.”

This latter point has been stressed by WHO in its guidelines for human challenge trials. It suggests the least risky group to infect would be those aged 18–30 years. Only 1% of this group end up hospitalised with Covid-19, while fatality rates are around 0.03%. “Challenge studies should then be conducted in specialised facilities, with especially close monitoring and ready access to early supportive treatment for participants,” add the guidelines.

The idea of carrying out human challenge trials for a Covid-19 vaccine was also backed by Professor Arpana Verma, of Manchester University. “Vaccines give us the ability to protect the most vulnerable people in society. That is one of their key strengths. So I think it would be entirely justifiable to go ahead with such trials.”

But the proposal was firmly opposed by immunologist Professor Eleanor Riley of Edinburgh University. “Challenge studies are done for many diseases but only when strict criteria are followed. Firstly, the virus should be really well studied and its clinical behaviour understood in detail. It should also be incapable of causing severe illness in healthy individuals, or there should be a highly effective drug to clear the infection. None of these criteria are met for Covid-19, and I would be very concerned to hear challenge studies were being planned.”

The crucial point is that we should be thinking now whether we want to go ahead with human challenge trials, said Young. “We shouldn’t wait until we have a vaccine candidate on our hands and not know what to do with it.”