Covid infection takes hold in just 42 hours, pioneering London study shows

Dozens of young adults were deliberately infected with Covid in the study
Ross Lydall @RossLydall2 February 2022

Covid starts to spread in the body far quicker than previously thought, pioneering UK research revealed on Wednesday.

Results from the world’s first “human challenge” study - in which healthy young adults were deliberately infected with Covid - found the average time between being exposed to the virus and it being detected was 42 hours.

This is far less than the five to six days “incubation period” estimated in official Government guidance.

Covid was found first in the throat but was then seen at “significantly” higher levels in the nose - highlighting the benefit of wearing a face mask to limit its spread.

The legal requirement to wear a mask was axed by the Government last Thursday but remains a “condition of carriage” on the Tube and London buses.

The study also supported the effectiveness of lateral flow tests, indicating they were able to detect Covid before 70 to 80 per cent of infectious virus had been generated and were a “good indicator” of a person’s infectivity.

A total of 36 volunteers aged 18 to 29 took part in the study last year at the Royal Free hospital, in Hampstead.

None reported serious illness nor side effects. Eighteen became infected, with viral load peaking five days after being exposed to the virus, which was administered via intra-nasal drops.

The original Wuhan or “Alpha” variant was used but researchers say the results “remain valuable” for Delta and Omicron.

The virus could be detected in the nose for up to 10 days on average after exposure - “supporting” longer isolation periods, rather than the five days currently in use. “Mild to moderate” symptoms were reported by 16 (89 per cent) of infected individuals.

The researchers said: “These data provide clear evidence that emphasises the critical importance of wearing face coverings over the nose as well as mouth.

“Furthermore, our data clearly show that viral shedding occurs at high levels irrespective of symptom severity, thus explaining the high transmissibility of this infection and emphasising that symptom severity cannot be considered a surrogate for transmission risk in this disease.”

The Human Challenge Programme was funded by the UK Government, with the study conducted by hVIVO at the Royal Free Hospital. Imperial College London was the clinical study sponsor.

Professor Christopher Chiu, of Imperial College and chief investigator on the trial, said: “People in this age group are believed to be major drivers of the pandemic.

“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.”

Professor Sir Jonathan Van-Tam, deputy chief medical officer for England, said: “Challenge studies could still prove to be important in the future to speed the development of ‘next-generation’ Covid-19 vaccines and antiviral drugs.

“This data underline just how useful a tool lateral flow tests can be to pick up people when infectious and the importance of wearing a face covering in crowded, enclosed spaces.”

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