A study with voluntarily infected people shows rapid incubation of COVID

A British study that investigated how the coronavirus operates in young and healthy patients, infected voluntarily, detected an incubation period “of about 42 hours”, shorter than the current estimate of between five to six days, and confirmed the efficacy of antigen tests to prevent spread.

The research, carried out by the so-called The Human Challenge program – where several institutions collaborate, such as the prestigious Imperial College in London – tracks the complete “modus operandi” of the coronavirus in young and healthy bodies.

It is the first study in the world to carry out detailed monitoring throughout the course of the infection, from the moment of exposure to the virus until it is eliminated.

Among the findings, the researchers observed that the symptoms begin to develop very quickly, about two days after infection, and that the infection first manifested itself in the throat; that the virus reached its peak after five days and that, then, it became more present in the nose.

They also verified that antigen tests are a reliable indicator to detect the presence of the virus.

The study, which has not yet been independently reviewed by the scientific community, details the evolution of the infection in 36 participants without prior immunity to the virus (due to having been vaccinated or infected), and was carried out in a specialized unit of the Royal Free Hospital of London.

“First and foremost, there were no serious symptoms or clinical concerns in our model of infection in healthy young adult participants,” said Christopher Chiu, from the Department of Infectious Diseases at the Institute of Infections at Imperial College London, who led the study.

The research reveals “very interesting clinical insights, particularly around the short incubation period of the virus, the extremely high viral shedding through the nose, as well as the usefulness of antigen tests, which have potential implications for public health.”

Thirty-six volunteers -men and women- between 18 and 30 years old, who were not vaccinated against the virus and had not had previous SARS-CoV-2 infections, were administered a low dose of coronavirus -extracted from a hospitalized patient at the beginning of the pandemic, and before the emergence of the alpha-variant, through drops through the nose. These were given a controlled follow-up for two weeks.

Of these, 18 became infected, and of these, 16 developed mild to moderate cold-like symptoms such as a blocked and runny nose, sneezing, and sore throat; others had headaches, muscle and joint aches, tiredness, and fever, but none developed severe symptoms.

Two participants were excluded when antibodies were detected before the virus inoculation, and thirteen lost their sense of taste and smell, although they recovered them again within a period of 90 days in all but 3 cases.

Among the most surprising findings, the experts saw that the period between the first exposure to the virus until its detection and the first symptoms (incubation) was 42 hours, “significantly shorter” than currently estimated, which points to an incubation of between five and six days.

On the importance of antigen tests, Chiu stressed that “although they could be less sensitive during the first or second day, if they are used correctly and repeatedly, and acted upon if they are positive, they will have a great impact when it comes to interrupting viral spread”.

He added that “although there are differences in transmissibility due to the emergence of variants, such as delta or omicron” “the study is fundamentally representative of this type of infection.”