It takes just a tiny virus-laden droplet – about the width of a human blood cell – to infect someone with Covid-19.
That’s just one of the findings from research that deliberately infected healthy volunteers with the SARS-CoV-2 virus.
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Under these carefully controlled conditions, researchers were able to learn a lot about the virus and how it moves through the body:
- Tiny amounts of virus, about 10 microns – the amount in a single droplet someone sneezes or coughs – can make someone sick.
- Covid-19 has a very short incubation period. It takes about two days after infection for a person to start shedding virus.
- People shed high amounts of virus before they show symptoms (confirming something epidemiologists had figured out).
- On average, the young, healthy study volunteers shed virus for 6½ days, but some shed virus for 12 days.
- Infected people can shed high levels of virus without any symptoms.
- About 40 hours after the virus was introduced, it could be detected in the back of the throat.
- It took about 58 hours for virus to show up on swabs from the nose, where it eventually grew to much higher levels.
- Lateral flow tests, the rapid at-home kind, work really well for detecting when a person is contagious. The study found that these kinds of tests could diagnose infection before 70% to 80% of viable virus had been generated.
