‘Human challenge’ Covid trial gives new insight into virus

Open Orphan test shows shorter incubation period, effectiveness of lateral flow tests

The world’s first “human challenge” trial that deliberately infects volunteers with Covid is safe in healthy young adults, the study has found.

The first data from the project, which is being run by Open Orphan with Imperial College London and the company's subsidiary hVivo along with Britain's Vaccine Taskforce and health authorities, also provided some insights into the course of Covid-19 infection.

The study revealed the incubation period observed was shorter than previously though, with the average time from exposure to detection of the virus and early symptoms at 42 hours rather than five to six days. High levels of the virus were seen for around nine days, but could be detected for up to 12 days.


On average, the virus was detected in the throat earlier, showing up after 40 hours, compared to 58 hours in the nose. However, peak levels of virus were far higher in the nose, underlining the importance of proper facemask use to cover both the mouth and nose.


As part of the study, 36 healthy male and female volunteers aged between 18 and 29 years old were exposed to the original Sars-CoV-2 strain of the virus and monitoredin a controlled quarantined setting.

Half the volunteers became infected, with viral peaking at five days post-inoculation after a steep rise. The study found no quantitative correlation between viral load and symptoms.

Most of those infected experienced mild-to-moderate cold-like symptoms, with 16 of the 18 reporting a stuffy or runny nose, sneezing, and a sore throat. Thirteen experienced anosmia – lost or changed sense of smell. No serious adverse events occurred over the course of the trial.

Encouragingly, the study indicated regular asymptomatic lateral flow testing would pick up infections before 70-80 per cent of infectious virus had been generated.

"While the characterisation study was focused on the original SARS-CoV-2 strain, and there are differences in transmissibility between it and the other variants, the same factors will be responsible for protection against it, meaning the findings remain valuable for variants such as Delta or Omicron," said Dr Andrew Catchpole, co-investigator on the study and chief scientific officer of hVIVO.


“These data provide a clear platform to now utilise the human challenge model to expedite product efficacy testing for new vaccines or antivirals.”

Cathal Friel, executive chairman of Open Orphan, said the results provided "invaluable insights" into Covid-19 disease progression and could help with the development of future treatments.

“Crucially, we have now successfully established a Covid-19 Human Challenge Model which could be instrumental in accelerating the development of future Covid-19 therapeutics,” he said. “New variants, such as Omicron, often mean that vaccines and antivirals have to be quickly re-evaluated to ensure effectiveness. Human challenge studies could prove to be the fastest way to compare old and new vaccines and therapies.”

The company is already developing a Delta strain of the Covid-19 virus in partnership with Imperial College London, which could be used in future trials.

Ciara O'Brien

Ciara O'Brien

Ciara O'Brien is an Irish Times business and technology journalist