Coronavirus: Study deliberately exposes people to COVID, finds that symptoms developed much quicker than thought

In a first-of-its-kind COVID-19 human challenge study, where healthy and young individuals were intentionally exposed to the coronavirus, UK scientists have found out that people developed the symptoms in less than 2 days after exposure. Only half of participants who were exposed to the coronavirus developed infections, with mostly mild symptoms, the study on 34 individuals, aged 18–30, has found.

People who were infected with the virus developed their first symptoms and tested positive, in less than two days after exposure, on average, the study found.

This contrasts with the 5 day incubation period that other studies have documented till now. High viral levels persisted for an average of 9 days, and sometimes up to 12, the study has found.

The results of the study have been posted on 2 February to the Research Square preprint server and have not been peer-reviewed.

The first group of participants were exposed to the virus in early 2021 and were quarantined at a high-level isolation unit at the Royal Free Hospital in London. The participants were exposed to a low dose of virus which is equivalent to the amount of virus in a single respiratory droplet.

The common symptoms were sore throats, runny noses and sneezing and fever was less common in the participants. No one developed the persistent cough. Fever and persistent cough are considered to be a hallmark of COVID-19 symptoms.

"Mild-to-moderate symptoms were reported by 16 (89%) infected individuals, beginning 2-4 days post-inoculation. Anosmia/dysosmia developed more gradually in 12 (67%) participants," the study has found.

The scientists have found that 18 individuals were infected with viral load rising and peaking at 5 days post-inoculation. Their study has found that a viable virus was recoverable from the nose up to 10 days post-inoculation. The study holds that the isolation period should be 10 days after the onset of the symptom in order to minimise further transmission.

The study has established that there is no quantitative correlation between viral load and symptoms.

It has said that lateral flow tests are a good indicator of viable viruses and can interrupt their spread. “However, lateral flow results were strongly associated with viable virus and modelling showed that twice-weekly rapid tests could diagnose infection before 70-80% of viable virus had been generated,” it has said.

In this study ancestral strain of the coronavirus was used. The team plans to launch another challenge trial that will expose vaccinated people to the Delta SARS-CoV-2 variant. That study will attempt to identify immune factors that protect people from ‘breakthrough’ infection after vaccination, as per a Nature report.

Human-challenge trial studies have been used earlier to study influenza, malaria and numerous other infections.