Live updates: follow the latest news on Covid-19 variant Omicron
A single nasal droplet of the coronavirus is enough to spread and see a person become infected with Covid-19 the world’s first “human challenge” study into the virus has found.
The trial, which deliberately exposed 36 healthy male and female volunteers aged 18-30 to the original strain of the coronavirus, could pave the way for future studies to test new vaccines and medicines to combat the virus.
The study also highlighted that lateral flow tests “are a reassuringly reliable indicator” of whether an infectious virus is present and therefore transmissible.
“Participants were exposed to the lowest possible dose of virus found to cause infection, roughly equivalent to the amount found in a single droplet of nasal fluid when participants were at their most infectious,” researchers said of their findings, which have not yet been peer reviewed.
Pharmaceutical group Open Orphan is carrying out the project with Imperial College London, the UK government's vaccine task force and the clinical company hVIVO.
“First and foremost, there were no severe symptoms or clinical concerns in our challenge infection model of healthy young adult participants,” said the trial’s lead investigator Prof Christopher Chiu, of Imperial College London.
“People in this age group [18-30] are believed to be major drivers of the pandemic and these studies, which are representative of mild infection, allow detailed investigation of the factors responsible for infection and pandemic spread.
“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.”
Of the three dozen people taking part, 18 became infected — 16 of whom experienced symptoms including a runny nose, sneezing and a sore throat. Some also suffered from head and body aches, fever and tiredness.
The study found that symptoms started to develop about two days after first contact with the virus. Infection first appeared in the throat while infectious virus peaked about five days into infection and, at that stage, was significantly more abundant in the nose than the throat.
With the volunteers, 13 temporarily lost their sense of smell but that returned within 90 days in all but three participants. The latter continue to show improvement after three months, researchers said.
There were no changes to the lungs.
