The US is preparing for a potential human challenge study for COVID-19 vaccines.

Government researchers are developing a strain of the coronavirus that would be used in these trials, where healthy participants are vaccinated then exposed to the virus to get infected.

READ: Why do vaccine trials take so long?

Usually, volunteers participating in vaccine trials are not asked to catch the virus, especially if there are many cases like in the current pandemic. This is why trials last for months.

“Should there be a need for human challenge studies to fully assess candidate vaccines or therapeutics for SARS-CoV-2, NIAID has begun investigations of the technical and ethical considerations of conducting human challenge studies,” the US National Institute of Allergy and Infectious Diseases told Reuters.

The trials would be conducted in small numbers and isolation units to control the disease, while those involving over 100 people would be done in multiple locations.

Johnson & Johnson (NYSE:JNJ) and AstraZeneca PLC (LON:AZN), which are also developing vaccine candidates, previously said they would consider these trials if needed.

Open Orphan PLC’s (LON:ORPH) hVIVO arm is set to start phase I of a human challenge trial for a nasal vaccine for coronavirus in the autumn.

It will quarantine 48 healthy young adults at a facility in London’s Whitechapel to assess whether the drug provokes an immune response.