Summaries and distillation of the current research that has been done and broadly circulated was a study done by a PhD at UMass that provided insight in particular to how airborne spread. Erin Bromage PhD provides the following:
A formula: Exposure to Virus x time = infection. provides a very insightful look at exactly how the virus spreads the the extent to which you are at risk in a variety of settings.
Most people get infected in their own home. A household member contracts the virus in the community and brings it into the house where sustained contact between household members leads to infection.
In order to get infected you need to get exposed to an infectious dose of the virus; based on infectious dose studies with MERS and SARS, some estimate that as few as 1000 SARS-CoV2 viral particles are needed for an infection to take hold. (this still needs to be determined experimentally, but we can use that number to demonstrate how infection can occur) Infection could occur, through 1000 viral particles you receive in one breath or from one eye-rub, or 100 viral particles inhaled with each breath over 10 breaths, or 10 viral particles with 100 breaths. Each of these situations can lead to an infection.
- A cough can hang in the air for minutes.
- Breathing emits particles
- A sneeze releases 30,000 droplets. They can travel across a room.
- If infected a sneeze can deliver 200 million droplets
- A breath can releases 50 to 5000 droplets.
- But with general breathing, 20 copies per minute into the environment, even if every virus ended up in your lungs, you would need 1000 copies divided by 20 copies per minute = 50 minutes.
- Speaking increases the release of respiratory droplets about 10 fold; ~200 copies of virus per minute. Again, assuming every virus is inhaled, it would take ~5 minutes of speaking face-to-face to receive the required dose.