Symptoms of COVID-19 develop “very fast” and on average two days after contact with the virus, according to a new study involving healthy young adults.
The Human Challenge Programme study, which has not been peer-reviewed, involved male and female volunteers aged 18-30 and is the first in the world to monitor the full course of COVID after infection.
Scientists also said the study found that lateral flow tests are a “reassuringly reliable indicator” of whether the “infectious virus is present” – but warned they are less effective in picking up lower levels of the virus at the very start and end of infection.
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Volunteers infected with COVID
The trial used virus from “very early in the pandemic” and before the emergence of the Alpha variant.
Each person was “exposed to the lowest possible dose” of the virus, introduced through nose drops, and then monitored for two weeks in a controlled environment.
Researchers said the infectious virus peaks after about five days when it is “significantly more abundant” in the nose and the throat.
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Eighteen volunteers became infected, 16 of whom went on to develop mild-to-moderate cold-like symptoms, including a stuffy or runny nose, sneezing, and a sore throat.
Some experienced headaches, muscle aches, tiredness and fever, but none developed serious symptoms.
All participants will be followed up for 12 months after leaving the clinical facility to monitor for any potential long-term effects.
Study reveals ‘interesting clinical insights’
Professor Christopher Chiu, from the Department of Infectious Disease and the Institute of Infection at Imperial College London and chief investigator on the trial, said: “There were no severe symptoms or clinical concerns in our challenge infection model of healthy young adult participants.
“People in this age group 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.”