Jeff Gilchrist Profile picture
Mar 22 20 tweets 4 min read Read on X
*** Ontario COVID Hospitalization Rates by Age ***

Data is now available for hospital admissions due to COVID by age group going back to Oct 2021. This provides interesting insights into how much children have been impacted with serious infections compared to adults. 🧵1/ Graph of New hospitalization rate in Ontario due to COVID by age group (100% Stacked).
Chart of COVID hospital admissions per 100k population by age group from Oct. 2021 to Aug. 2025 in Ontario, Ottawa, and Toronto.
We have heard from many sources throughout the pandemic that COVID isn't serious in children or they are not impacted as much as adults with some people still claiming this today. 2/
What about today, with lower circulation happening more recently and not the huge waves seen in the past, is anyone even being hospitalized for COVID anymore? The most recent update (week of March 8, 2026) there were 188 people hospitalized in Ontario due to COVID. 3/
Looking at age groups, those age 75+ had the highest rates of hospitalization due to COVID while second place was age 65-74 and age 0-4 had the third highest rate, all increasing since the last update. 4/
Right now, the youngest age group 0-4 currently have a hospitalization rate due to COVID that are 9x higher than age 5-17, 9x higher than age 18-49, and 2.6x higher than adults 50-64. 5/
You can see from the graph that children age 0-4 actually make up a significant percentage of hospital admissions due to COVID. The rate for age 0-4 is often similar to and sometimes even higher than the 65-74 age group. 6/ Graph of New hospitalization rate in Ontario due to COVID by age group (100% Stacked).
This graph shows data from Sept. 2025 to present and since Ontario changed the age categories, it is not directly comparable to earlier historical data. 7/
While hospitalization rates have changed throughout the pandemic, what does the picture look like if we examine Oct 2021 to August 2025 all together with the previous age group categories? 8/
This second graph shows COVID hospital admission rates due to COVID for the province of Ontario (population ~14M), Ottawa Public Health (population ~1M) and Toronto Public Health (population ~2.7M). 9/ Chart of COVID hospital admissions per 100k population by age group from Oct. 2021 to Aug. 2025 in Ontario, Ottawa, and Toronto.
The first thing that jumps out is that locations had significant differences in hospitalization for children and the oldest adult populations. 10/
For whatever reason, Ottawa had almost double the rate of hospitalization for children, while significantly lower rates for ages 18-39 and 80+ compared to Toronto and Ontario as a whole. 11/
The age 0-4 group had the highest rates of hospitalization among children so we will use that as the comparison. 12/
The age 80+ group had by far the highest hospitalization rate for COVID, 13.7x higher in Ontario than age 0-4 with the second highest coming from age 60-79 which was 2.7x higher than age 0-4. 13/
Children age 0-4 had the third highest rate of any age group. In Ontario, children age 0-4 had rates 7.4x higher than age 5-11, 5.2x higher than age 12-17, 2x higher than adults age 18-39 and 1.5x higher than adults 40-59. 14/ Chart of COVID hospital admission ratio per 100k population comparing age 0-4 to the 12-59 age groups from Oct. 2021 to Aug. 2025 in Ontario, Ottawa, and Toronto.
In Ottawa there was an even bigger difference compared to adults with children age 0-4 being hospitalized at rates 4.5x higher than age 18-39 and 2.9x higher than age 40-59. Children age 5-17 had similar hospitalization rates to adults 18-39. 15/
Clearly children, especially our youngest, can become seriously ill when infected with COVID requiring hospitalization and these elevated rates continue today with children age 0-4 being the third and sometimes second highest among all age groups. 16/
This isn't even taking into account the long-term damage that COVID infection can cause in children who aren't hospitalized and unborn fetuses which make up a much larger proportion of the population than those that are hospitalized. 17/
You can find my weekly Ontario stats including variants at ( ). 18/covid.gilchrist.ca/Ontario.html
The hospitalization source data used in this post can be found from PHO ( ). 19/publichealthontario.ca/en/Data-and-An…
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More from @jeffgilchrist

Mar 14
*** Ontario Virus & Variant Update | Mar 14 ***

Hospitalizations due to COVID have gone down from 190 to 138 in the last update. Influenza hospitalizations remained stable around 49 and RSV decreased slightly from 194 to 184. 🧵1/

#Ontario #Virus #Variant #COVID #RSV #Influenza Graph of New hospitalizations in Ontario due to COVID, Influenza or RSV.
Looking at age groups, those age 75+ had the highest rates of hospitalization due to COVID but decreased since last update. Second place is age 65-74 and their levels are currently decreasing while age 0-4 has the third highest rate and also decreased since last update. 2/ Graph of New hospitalization rate in Ontario due to COVID by age group (100% Stacked).
The youngest age group 0-4 currently have a hospitalization rate due to COVID that are 11x higher than age 5-17, 5.5x higher than age 18-49, and 2x higher than adults 50-64. 3/
Read 16 tweets
Jan 11
*** Ontario Virus & Variant Update | Jan 11 ***

Hospitalizations due to COVID increased from 176 to 241 in the last update. Influenza hospitalizations have start dropping from the peak of 1,400 to 1,095 with RSV increasing from 121 to 156. 🧵1/ Graph of New hospitalizations in Ontario due to COVID, Influenza or RSV.
Looking back over the past few years, new hospitalizations for RSV have remained pretty stable the last two years around 2,500 and a decrease from 2023, while COVID has been significantly dropping each year, 26,571 in 2023 to 15,739 in 2024 to 6,788 in 2025. 2/ Graph of New hospitalizations in Ontario due to COVID, Influenza or RSV, grouped by calendar year.
Influenza has been doing the opposite, increasing significantly each year from 3,486, to 4,380 in 2024, to 12,818 in 2025. 3/
Read 13 tweets
Oct 25, 2025
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
Oct 19, 2025
** 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
Sep 9, 2025
*** 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
Jun 9, 2025
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

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