Volunteers have extensive medical checks and are fully informed of the risks before participating. Doctors are also on hand 24 hours a day to monitor all participants and step in as required.
At the end of the trial, volunteers receive a course of antibiotics to eradicate any remaining bacteria, irrespective of whether they became unwell.
Typhoid is not the only disease volunteers are risking in the name of science. At the Liverpool School of Tropical Medicine (LSTM), around 1,250 volunteers have inhaled live pneumococcal bacteria – which can cause pneumonia – as part of a challenge trial.
“There are 90-plus strains of pneumococcal bacteria,” said Dr Andrea Collins, senior clinical lecturer at the LSTM. “Current vaccines in the UK protect adults against 23 strains, and children 13. We are still very much exposed. Our aim is to develop a vaccine with all 90 serotypes.”
Pneumonia is the leading killer of children under five worldwide, with 1.4 million dying from the preventable disease last year.
Volunteers in the study, who are predominantly students from Liverpool’s universities, are paid between £200 and £600 for taking part. But nobody has ever become ill in the trial, which tracks natural and vaccine-derived immunity based on whether participants become carriers of the disease.
Hannah Browne, a 23-year-old medical student at Liverpool University, is currently taking part in one of the pneumococcal vaccine trials in return for £380.
“I was intrigued about rising [disease] resistance so got involved,” she told The Telegraph. “But I’m a student so there was also a strong financial incentive. Every little helps.”
She added that having the bacteria squirted up her nose “tickled a bit” but was not painful.
Similar studies are likely to become more common. The Medical Research Council has established a new programme, Hic-Vac, which provides £100,000 grants to support scientists setting up challenge trials. The project is also creating a global network of researchers to share advice and insights about how to run a successful study.