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Jeff Gilchrist Profile picture
@jeffgilchrist
Jun 21, 2022 • 8 tweets • 3 min read • Read on X
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COVID-19: Comic and video explanation of transmission

Multiple years into the pandemic and many still don't understand how the airborne transmission of respiratory viruses like COVID-19 work. 🧵1/
The Aerosol Science Research Center in Taiwan has put together an explainer comic and video for people to more easily understand ( aerosol.nsysu.edu.tw/en/scopes/108 ). 2/
The youtube video can be found here ( ). 3/
Hopefully this will help people understand that being in a closed meeting room of people for multiple hours with people spaced exactly 2m apart is not sufficient to prevent transmission from a virus that travels in the air. 4/
With poor ventilation those virosols (virus-laden aerosols) can remain in the air for hours so you might even get infected by someone who was in the previous meeting and is not even there any more. 5/
Surface cleaning does *not* stop airborne transmission and physical barriers like plexiglass can actually disrupt air flow and trap higher concentrations of aerosols making things worse. 6/
How do you reduce the chance of airborne transmission?
- improve ventilation & air filtration
- wear mask with proper fit (N95 or better)
- avoid clustering
- keep physical distance (2m is not sufficient for aerosols)

7/
"We are exposed to massively more pollutants, toxins, and pathogens via air than food and water." so fixing and improving air quality helps with so much more than just COVID-19 ( ). Image by @akm5376 8/

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More from @jeffgilchrist

Jeff Gilchrist Profile picture
Oct 25
How does various mask fit compare to filter the air and protect you or others?

Most masks, even baggy blue procedure masks use filtering material that can filter 95%+ of particles that pass through it, but the key is "pass through it". 🧵1/ Bar chart titled “Equivalent Exposure Time to Unmasked Person.” The chart compares how long different masks/respirators extend the equivalent exposure time relative to being unmasked. The x-axis shows unmasked infection times of 1, 5, and 10 minutes. The y-axis shows equivalent masked exposure time, ranging up to 5000 minutes. Seven mask types are represented by colored bars: - Procedure mask (loose fit, FF=2) - Ear loop mask (tight fit, FF=6) - Vertical bifold headband mask (FF=30) - N95 headband masks with fit factors of 100, 200, and 500 Key pattern: higher fit factor masks dramatically ...
Protection mostly depends on how well that mask fits your specific face and one that does not fit well, much of the air you breathe will go around the filter material and filter 0% of those particles. 2/
There has been a chart going around recently that talks about "Time it takes to transmit an infectious dose of COVID-19" which is misleading if you don't understand all of the details of how that table was made and what each component means. 3/
Read 25 tweets
Jeff Gilchrist Profile picture
Oct 19
** Ontario Variant Update (to Oct. 3, 2025) **

The XFG.* "Stratus" family is accounting for 83% while the next closest variant family NB.1.8.1.* "Nimbus" is 12.8% of sequenced genomes from COVID tests. 🧵1/ Line graph showing COVID-19 variant family frequencies in Ontario, Canada, from June to October 2025, based on 3,722 sequenced genomes.
Looking at specific variants, XFG.3 has dropped considerably and its descendent XFG.3.15 now takes first place at 6.2%, followed by XFG.3 at 5.2% and XFG.2 at 4.5%. 2/ Line graph showing specific COVID-19 variant frequencies in Ontario, Canada, from June to October 2025, based on 3,722 sequenced genomes.
It looks like PY.1.1.1 was trying to make a run for the top in mid-September but has decreased significantly. PY.1.1.1 is a descendant of LF.7 while the XFG variant is a recombination of LF.7 and LP.8.1.2 so they would share some mutations in common. 3/
Read 10 tweets
Jeff Gilchrist Profile picture
Sep 9
*** Ontario Variant Update (to: Aug. 16, 2025) ***

Ontario COVID sequence updates have been more frequent over the past month with the XFG.* "Stratus" family of variants now at 74% of sequences, NB.1.8.1.* "Nimbus" at 22% and LP.8.1.* down to 3%. #Variants #XFG #Stratus 🧵1/ Line graph showing COVID-19 variant frequencies in Ontario, Canada, from May to mid August 2025, based on 1,772 sequenced genomes. The XFG.* Stratus variant rises sharply to dominate over 70% by August. Other variants, including FLiRT and LP.8.1.*, decline over the same period, while NB.1.8.1.* Nimbus remains steady around 20% and several minor variants remain at low levels.
Looking at specific variants as of mid August, XFG.5.1 is most prevalent at 13%, NB.1.8.1 in second at 10%, XFG.2 in third at 8.6% and XFG.3 in fourth at 7.4%. 2/ Line graph showing COVID-19 variant frequencies in Ontario from 5 July to 16 August 2025, based on 750 sequenced genomes. Seven variants are tracked: NB.1.8.1, XFG.2, XFG.3, XFG.3.4.1, XFG.3.1, XFG.4.1, and XFG.5.1. Frequencies range from 0% to about 14%, with some variants rising, others falling, and some fluctuating over time. A bar chart below shows the number of samples collected on each date.
LP.8.1 is what this fall's Japan Novavax vaccine and the mRNA vaccines are designed for which is now almost gone and typical of how these things work with vaccine manufacturing timing while Novavax is providing the previous year's JN.1 vaccine formula for the USA again. 3/
Read 18 tweets
Jeff Gilchrist Profile picture
Jun 9
Understanding Canadian Air Quality Health Index (AQHI) & Wildfire Smoke

Wildfire smoke consists of toxic gases and particulate matter (PM) when breathed in gets into our lungs, bloodstream, and even our brain. 🧵1/
#iaq #wildfire #smoke #AQI #AQHI #Canada Bar chart of Canadian Air Quality Health Index (AQHI) - Equivalent # Cigarettes after Exposure ranging from 0.5 cigarettes after 8 hours exposure at AQHI level 3 to 0.9 cigarettes at level 6 and 1.5 at level 10.
Graph of Particulate Matter (PM) Levels in Ottawa from June 6, 2025 to June 8, 2025 from a VisiblAir Model X air quality sensor ( https://visiblair.com/ ).
The web version of this article with nice table of contents and easy to share with others can be found here ( tinyurl.com/AQHIwildfire ) and ( docs.google.com/document/d/1s9… ). 2/ Table of Contents: * Introduction * Air Quality Health Index (AQHI) * Health impact of Wildfire Smoke * Protect Yourself
When smoke stays in the air for prolonged periods of time, the UV radiation from the sun interacts with all the volatile organic compounds (VOCs) to form even more toxic gases ( ). 3/theweathernetwork.com/en/news/weathe…
Read 41 tweets
Jeff Gilchrist Profile picture
Jun 6
Pollution levels in Ottawa are very high from wildfire smoke. The particulate matter (PM)2.5 levels surpassed 140 ug/m^3 Thursday evening and are still above 130 on my VisiblAir Model X outdoor sensor ( ). 🧵1/ #iaq #wildfire #smoke visiblair.comLine graph showing PM2.5 levels in Ottawa increasing above 140 ug/m^3 and still above 130 now
Readings from a VisiblAir Model X outdoor air quality monitor showing levels in Ottawa above 130 ug/m^3 for PM2.5 wildfire smoke pollution
The EPA maps fine particulate pollution to their Air Quality Index where anything above 125.5 PM is Very Unhealthy which is a "Health alert: The risk of health effects is increased for everyone" ( ). 2/airnow.gov/aqi/aqi-basics/
EPA Categories:
* Unhealthy for Sensitive Groups (Orange) = 35.5-55.4 PM ug/m^3
* Unhealthy for everyone (Red) = 55.5 to 125.4 PM ug/m^3
* Very Unhealthy (Purple) = 125.5 to 225.4 PM ug/m^3
* Hazardous (Brown) = 225.5+ PM ug/m^3

3/
Read 13 tweets
Jeff Gilchrist Profile picture
Feb 10
#Ottawa, #Ontario, #Canada Virus Update:

You can see in the graph, COVID makes up the majority of new hospitalizations due to #Flu, #RSV or #COVID throughout the year, and even stays ahead during winter respiratory virus season. 🧵1/ A line graph displaying the percentage of patients hospitalized due to COVID-19, Influenza, or RSV over time, from September 1, 2023, to January 26, 2025. The x-axis represents weeks within this period, and the y-axis shows percentages from 0% to 100%. The graph has three colored lines: blue for COVID-19, purple for Influenza, and teal for RSV. The graph shows fluctuations in the percentage of hospitalizations due to each cause over time, with COVID-19 consistently having the highest percentage, followed by Influenza and RSV.
New hospitalizations are increasing again. This last update was the first time Flu hospitalizations (42) were significantly higher than COVID (34) in the same week with RSV at 14 people. 2/ The bar chart shows the number of new hospitalizations per week in Ottawa from August 27, 2023, to January 26, 2025. The y-axis represents the number of patients, ranging from 0 to 100. The x-axis represents the weeks. The bars are color-coded: blue for COVID-19, purple for Influenza, and teal for RSV. The chart shows fluctuations in hospitalizations over time, with notable peaks around December 2023 and January 2025.
In Ottawa, test positivity for Flu A (bright green) has really increased, COVID is still in second place, but seasonal human coronavirus is almost the same level, followed by Entero/Rhinovirus, and then RSV for the top 5. 3/ A stacked area chart displaying the percentage of positive tests for various viruses over time, from October 1, 2022, to January 26, 2025. The x-axis represents weeks within this period, while the y-axis represents the percentage, cumulatively stacked to 100%. The chart features the following viruses, each depicted in a distinct color: COVID-19 (red), Entero/Rhinovirus (yellow), Seasonal human coronavirus (purple), RSV (green), Parainfluenza (all types) (blue), Influenza B (dark purple), Influenza A (light green), Human metapneumovirus (pink), and Adenovirus (dark blue). The data shows fluc...
Read 6 tweets

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