The Spread of COVID-19: New facts in the Journal Science

An article this week in one of the most prestigious scientific journals in the world, Science, shares what we have learned so far about how COVID-19 (SARS-CoV-2) is transmitted. Science is published by the American Association for the Advancement of Science (AAAS) and this article, like all scientific articles about COVID-19 are freely available to the public to download and read! This information is provided as a service to the scientific community to continue to advance COVID-19 research. An added bonus is that anyone in the world with an internet connection can access and read these articles getting a glimpse into how scientific research is conducted! For example, there are references in this article to the original studies showing that masking reduced viral transmission.

Click here to read the article.

Collaborative scientists in San Diego and Taiwan share new observations that the droplets that transmit COVID-19 are very small, much smaller than originally thought.


The bad news is that COVID-19 can stay airborne and travel much farther that originally thought so 6 ft is probably not far enough to social distance, especially indoors. The size of the particles is about the same as the particles produced in smoking - so if you can smell cigarette smoke then that same person could infect you if they had the virus.

The good news is that scientific studies as well as anecdotal evidence clearly show that if unsuspecting infected individuals wear a mask, the number of viral particles in the air is significantly reduced! This is why everyone is encouraged to wear a mask.




There are several key takeaways from this review of the scientific literature from the observation that SARS-CoV-2 (COVID-19) can be transmitted in much smaller droplets that other viruses, like influenza (the flu). This has some important implications as we start venturing out.

  1. The small size of the droplets allows the virus to be breathed directly into the lungs. Initial infection in the lungs allows the virus to be breathed out in droplets at high concentrations before onset of symptoms. This is the now well-publicized observation that people who seem perfectly healthy can infect others for several days before they know they have the disease.

  2. Because the droplets are smaller than expected, they are lighter and can travel farther than 6 ft. Larger particles like for the flu settle within 4.6 seconds and within 6 feet. The smaller COVID-19 droplets can stay airborne for 12.4 hours. This means that COVID-19 could be travelling much farther especially indoors.

  3. A model of cigarette smoke is used as an example of COVID-19 travelling in a room because smoke particles are about the same size as the smaller COVID-19 droplets. If you can smell smoke from the person, you could get infected.

  4. The good news is that masks significantly reduce the number of virus particles in the air! This includes well-fitting homemade masks. Places like Taiwan, Hong Kong, Singapore and South Korea instituted mandatory mask wearing early in the pandemic and had significantly lower infection and death rates than other countries.


Scientists are still studying how far the virus can travel outside in the sunlight and how many virus particles are required to infect a person.


Stay tuned and stay safe Science Rangers!