Low level of virus in UK impacts trials

United Kingdom researchers are having to test COVID-19 vaccines abroad because novel coronavirus levels are too low in the British population, a UK parliamentary committee heard this week.

Human trials for ChAdOx1 nCoV-19, which is more commonly known as the Oxford vaccine, will commence this week in South Africa, where the number of COVID-19 cases has risen rapidly in June. The Oxford vaccine will also enter human trials later this year in the United States.

Meanwhile, developers of a separate vaccine at Imperial College London are looking to launch human trials in Brazil, a country that has contended with a comparatively high transmission rate for several months. Human trials for the Oxford vaccine have already begun in Brazil.

Moving human trials abroad is necessary because, in the UK, not enough people would come into contact with the virus to challenge vaccine efficacy, according to Sarah Gilbert, a professor of vaccinology at Oxford University who is leading the development of ChAdOx1 nCoV-19.

Gilbert and her colleagues had been hoping to get preliminary results from UK human trials in April. However, transmission was so high in March that the UK went into lockdown.

Movement restrictions in the UK then drove down the transmission rate to the point where human trials would have "little chance of determining efficacy" in a vaccine, Gilbert said. The Oxford team has now had to look abroad, and multiple countries have come forward.

"There hasn't been any lack of other countries wanting to partner with us," Gilbert told the House of Lords Science and Technology Committee. "We have chosen to work with Brazil because of previous experience of working with the clinical trial team there."

Immunologist Robin Shattock, who is leading the development of a vaccine at Imperial College London, said he is also targeting Brazil for human trials.

"We hopefully will look to do the same," Shattock said. "It's really about getting those numbers to be able to show that the vaccine works."

Gilbert said that pharmaceutical company AstraZeneca, which is partnering on the Oxford vaccine, is hoping to coordinate a US-based trial involving 30,000 people "in the coming months". The exact location in the US will be based on virus transmission rates.

Picking a country or region for testing is further complicated due to the timeline of a trial, according to Gilbert. In an ideal world, virus transmission would be high in a region several weeks after people have been given the vaccine, allowing time for them to develop antibodies and other immune responses stimulated by the inoculation.

"The problem for us is not knowing where virus transmission is now, it's knowing where it's going to be in four to six weeks' time," Gilbert said.

Some experts believe that alternative — and more controversial — forms of vaccine trials should be explored, given the challenges associated with conventional field testing. London-based lab hVIVO is looking to gain approval from UK drug regulators to run so-called human challenge trials, where paid volunteers are intentionally exposed to the virus in order to test vaccine protection.

Cathal Friel, chief executive of hVIVO parent company Open Orphan, told China Daily that opening up such trials "has to be one of the options considered".