"Challenge" Study Shows How the Virus Gets You

 

A couple of days ago Nature Medicine published results of a "challenge study" where they deliberately infected healthy people with the OG strain of SARS-CoV-2. The purpose of the study was to learn more about the course of an infection with the virus.

Researchers recruited 36 volunteers aged between 18 and 30, who had no known risk factors for severe disease. There was extensive informed consent to make sure participants knew what they were getting into. They also had supplies of antibody treatments available in case anyone got seriously ill.

Participants were then given a tiny drop of fluid containing the virus—an amount comparable to what you might get from an aerosol droplet expelled by an infected person. They were then monitored around the clock for two weeks in a hospital setting.

The results are very interesting. None of the participants developed severe disease, and only half of them even became infected. So either getting infected once exposed is a 50/50 proposition, or there was something keeping half of them from getting ill. Scientists have been trying to understand why some people never get the disease.

Of the 18 people who did become infected, two of them had no symptoms. Fifteen of them had some degree of loss of sense of smell, and nine had a complete loss. 

Those infected had a very short incubation period of about two days. As epidemiologists had already figured out must be the case, participants who never developed symptoms still shed large amounts of the virus. Those who eventually developed symptoms shed large amounts of the virus for about two days before they did so. On average they shed virus for 6.5 days, but at the extreme it was 12 days. 

The study also shed some light on testing. Back-of-throat swabs detected the virus 18 hours sooner than nasal swabs. Also those "lateral flow" rapid tests, about which I have blogged my skepticism before, turned out to be good at detecting that people were contagious at a point where they had only generated 20%-30% of the maximum viral load.

My takeaways from this are, first, that exposure is not a sure thing in terms of getting infected. Second, this virus is especially nasty because people can shed it in large amounts for days, even before they show symptoms. Both of these things suggest to me that it remains wise to be conservative about going maskless.

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