Amazing to see decent public health advice for once.

All masks are not equal, so it’s great to see Frosty the Snowman here wearing a high quality, well-fitted N95 mask.

#BeLikeFrosty ⛄️

Read on in this thread 🧵 to find out more about the wonders of N95 masks…
The study below compared the fitted filtration efficiency of surgical masks vs N95 masks:

📍Surgical mask: 38.1%
📍N95 respirator: 98.5%

As you can see, surgical masks have vastly inferior fitted filtration efficiencies compared to high quality N95s.

jamanetwork.com/journals/jamai…
Image
The physics of masks is very interesting.

N95’s filter out:

📍~100% of tiny particles (<0.1μm) through Brownian diffusion

📍~100% of the larger particles (>1.0μm) through interception

📍medium particles (~0.3μm) are trickier but an N95 mask will still filter out 95% of these. Image
To understand this in more detail, this brilliant video from @minutephysics explains the genius physics behind N95 masks and how they work to protect you against even the tiniest fine particles.

TLDR: They work more like magnets than like sieves.


Image
There are a number of mechanisms in action within N95 masks which contribute to their filtration efficiency, including:

📍gravity sedimentation
📍inertial impaction
📍interception
📍diffusion
📍electrostatic attraction

You can read more about this here:

sciencedirect.com/science/articl…
Image
Oh, and just in case you’re getting confused about all the mask terminology (N95, N99, FFP2, FFP3 etc), this is a really useful explainer from the good folks @SmartAirFilters:

Broadly speaking, an N95 is similar to the European FFP2 standard.

smartairfilters.com/en/blog/compar…
Image

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More from @_CatintheHat

Jan 30
🏴󠁧󠁢󠁥󠁮󠁧󠁿PUPIL ABSENCE - AUTUMN 2025

The DfE have now published pupil absence data for the Autumn term:

🔎 Pupil illness absence across the autumn term averaged out at 3.44% (compared to pre-pandemic average of 2.5%).

🔎 By the end of Nov, illness absence had soared to 4.7%.

🧵 Image
DfE commentary:

“The increases seen in the latter weeks of term were mainly driven by illness-related absence”

“This increase in absence is equivalent to approximately 500,000 less days in school compared to the previous autumn term.”

…e-education-statistics.service.gov.uk/find-statistic…Image
To anyone paying attention, these illness absence figures should not come as a surprise.

By early December, UKHSA was warning about how flu was spreading like wildfire through classrooms, leading to very high infection rates in school-age children (pink & green lines on chart). Image
Read 10 tweets
Jan 4
COVID & CHILD DEVELOPMENT

New US study showing impact on child brain development when their mothers are infected with COVID during pregnancy.

Results show:
🔎 Structural differences in regions of the brain
🔎Lower cognition & social-emotional scores

sciencedirect.com/science/articl… x.com/harryspoelstra…Image
And here’s another study, this time from Brazil (published Jun 2025), which also shows the impact of maternal COVID infection on child development.

At 24 months:
🔎 36% of infants exhibited cognitive delays
🔎 64% communication delays
🔎 57% motor delays

nature.com/articles/s4139…Image
And another study, just published this week (Jan 2026) in ‘Obstetrics & Gynecology’, came to similar conclusions…

“Maternal SARS-CoV-2 infection in pregnancy was associated with increased risk of adverse neurodevelopmental diagnoses by age 3 years”.

journals.lww.com/greenjournal/f… x.com/jama_current/s…Image
Read 4 tweets
Dec 17, 2025
“When it comes to flu, the focus is often on droplet transmission, but there’s also evidence of aerosol transmission. That means that ventilation & air filtration are HUGELY important.

“Are the Govt looking to improve that to help deal with all the respiratory infections?”

/1
It’s absolutely brilliant to hear Baroness Bennett raising this crucial question in the House of Lords this week.

Thank you, @natalieben 🙏🏻

You can read a transcript of the full question and response received below ⬇️



/2 hansard.parliament.uk/Lords/2025-12-…Image
Given the shocking state of ventilation in UK hospitals ⬇️…

3/
Read 4 tweets
Dec 11, 2025
This feels like an important breakthrough moment…

On the BBC News this evening, Medical Editor @BBCFergusWalsh clearly stated:

“As for facemasks, simple surgical masks are *not* good at stopping viruses. You really need a properly fitted tight respirator mask for that”…

/1
…which begs the question, why does the NHS infection control guidance STILL only recommend surgical masks for treating patients with airborne viruses like flu & Covid… and not proper FFP3 masks?

Even Baroness Hallett was rather perplexed by this during the Covid Inquiry.

/2
The IPC experts (Dr Warne & Dr Shin) who provided independent specialist advice to the Covid Inquiry both stated that IPC guidelines should be updated to recommend routine use of FFP3 masks when caring for patients with ANY respiratory virus.

So why has this not been done?

/3
Read 7 tweets
Dec 10, 2025
CEO, NHS Providers, @danielelkeles:

“It’s a v nasty variant of flu that we have this year.”

“We need to get back into the habit that, if you’re coughing & sneezing […] then you must wear a mask when you’re in public spaces.”

I’m so pleased to hear Daniel promoting masks BUT…
…I have 3 questions for @danielelkeles:

1️⃣ He only mentions that people who are sick “must wear a mask in public spaces”…

…but why did he not also suggest that people who are *not* sick should wear a mask to prevent themselves getting sick in the first place?!

Like this ⬇️ Image
2️⃣ Why didn’t @danielelkeles mention FFP masks?

Surgical masks DON’T protect against airborne transmission of flu.

“Live viruses could be detected in the air behind ALL surgical masks tested. By contrast, properly fitted respirators could provide at least a 100-fold reduction.” Image
Read 5 tweets
Dec 8, 2025
UK ‘SUPERFLU’ OUTBREAK

Schools in England & Wales have been forced to close amid escalating flu outbreaks with hundreds of pupils off sick at a time.

Simon Kidwell, headteacher of Hartford Manor Primary told BBC Breakfast: “The winter bugs spread really easily in schools”…

/1
Headteacher Simon Kidwell is not wrong.

Children are crammed into poorly ventilated classrooms, shoulder-to-shoulder with up to 29 other kids, for around 6 hours a day, 5 days a week.

It’s the perfect environment for airborne diseases to spread…

/2 Image
We had a big wave of Covid in Sept/Oct, followed in very quick succession by the current wave of flu and RSV.

It’s been one perpetual cycle of illness hammering schools.

I often hear people say: “oh, but it’s always been like this”.

But it *hasn’t* always been like this.

/3 Image
Read 18 tweets

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