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COVID questions: airborne particles; vaccines for children

October 7, 2021 By Kristina LeVan

Editor’s note: This ongoing series answers questions about COVID-19 and the pandemic. If you have a question to submit, please email it to See answers to previous COVID questions at Also, visit our COVID-19 impact site.

I’m curious if there’s any information or data about how long the virus can linger in the air. For instance, if someone who is carrying the virus (knowingly or not) is in their room by themselves without a mask, would someone else entering that room some time later be at risk of breathing in enough virus to get infected?

Exhaled respiratory particles, which can contain the SARS-CoV-2 virus, range in size from sub-micrometer in diameter to hundreds of micrometers. Those at the large end of this spectrum deposit quickly to surfaces near their source. The smaller particles persist much longer as they are distributed through the room and are removed either through ventilation or in-room filtration. It has been shown that the virus remains viable in suspended particles indoors for more than an hour. In rooms with good ventilation and/or in-room filtration, the amount of virus present in the air may be cut in half in less than 10 minutes. For rooms with inadequate ventilation, this time could be more than an hour.

So yes, it is possible that a person who enters a room occupied by an infected individual, who just donned a mask upon their visitor’s arrival, could be at risk. An analogy would be to think of a person smoking in their room. If they extinguish the cigarette upon arrival of their guest, the guest will still inhale the smoke until eventually the room’s ventilation system or in-room filtration removes it from air.

—Timothy Bertram, Professor, Chemistry; Affiliate Professor Atmospheric and Oceanic Sciences; Environmental Chemistry and Technology 

The Pfizer vaccine has been approved for emergency use in people 12 and older, and clinical trial data was recently submitted to the FDA for use in kid ages 5-11. How safe are COVID vaccines for children and teenagers?

The vaccine was very well studied. We know there are some rare adverse events that can happen in the teenage population, but overall, the vaccine is very safe and effective.

The process for approving vaccines under the Emergency Use Authorization is basically identical to how you would do it during regular times. The difference is we were able to accumulate a lot more children very quickly for that study, and for the adult studies as well, so the safety issues are quite well established with these vaccines. The FDA is continuously monitoring for unusual side effects even after vaccines are authorized. All reports are taken seriously and investigated thoroughly.

—Greg DeMuri, pediatrician at UW Health, from UW Health News