Detection of the virus in infected individuals came initially by using throat swabs, about 40 hours after contact, researchers said. Detection in the nose came about 58 hours post-contact.
Viral loads increased rapidly following detection, peaking about six days following contact with the virus.
Many health bodies around the world, including the U.S. Centers for Disease Control and Prevention, say symptoms can develop in two days but also describe a window that can last as long as 14 days following exposure to the illness.
The 36 participants in the study were aged 18 to 29 and had no evidence of previous infection or vaccination.
Half became infected and all but two of those showed symptoms.
Symptoms included loss of smell, which lingered in three participants past 90 days.
No serious adverse events were recorded and no lung issues were detected.
Participants were deliberately infected, but with an amount of virus described as “the lowest possible dose” to cause infection. The amount was roughly the same as that found in a droplet of nasal fluid when volunteers had peak viral load. The virus was wild-type, pre Alpha.
The human challenge trial was performed at Royal Free Hospital in London by British researchers, including some from Imperial College London, with government backing.
“Our study reveals some very interesting clinical insights, particularly around the short incubation period of the virus, extremely high viral shedding from the nose, as well as the utility of lateral flow tests, with potential implications for public health,” Christopher Chiu, professor at the Institute of Infection at Imperial College London, said in a statement.
“The trial has already provided some fascinating new insights into SARS-CoV2 infection, but perhaps its greatest contribution is to open up a new way to study the infection and the immune responses to it in great detail and help test new vaccines and treatments," Dr. Michael Jacobs, consultant in infectious diseases at the Royal Free London NHS Foundation Trust, one of the collaborating institutions, added.
SARS-CoV-2 is another name for the CCP virus.
Lawrence Young, a virologist and professor of molecular oncology at the Warwick Medical School, who was not involved with the study, said the groundbreaking study “reinforces observations from previous studies of natural infection confirming rapid onset of upper respiratory tract infection after 2 days but shows that high levels of virus are produced in the throat before being detected in the nose.”
