Study: Air purifier use at daycare centres cut kids' sick days by a third (2023)

There's no good evidence for "you need to get sick in order to have a healthy immune system", and it leads to dangerous nonsense like measles parties.

What you've written is unproven, and I see two facets of confusion:

First, there's a huge difference between "strong" immune responses and "good" immune responses.

Triggering the adaptive immune system is dangerous, like unleashing Skynet robots against a zombie apocalypse. You don't nuke a city at the first police report of one person biting another. Your body has a ton of cascading safety interlocks to try to avoid triggering more than is absolutely necessary.

Second, there's a difference between "we need dangerous exposure to actual pathogens" versus "we need calibration against a mileu of benign species we co-evolved with."

There's no evidence our immune systems are somehow "weaker" than our ancestors', but they do seem to be miscalibrated and trigger-happy.

This is a common misunderstanding of the poorly-named “hygiene hypothesis”. For a fuller explanation of how immunologists think about this today, see this article: https://rachel.fast.ai/posts/2024-08-13-crowds-vs-friends/

In short - viruses can actually harm your immune system and lead to long term problems. OTOH, we co-evolved with certain parasites that can help us.

Airborne pathogens are not likely to be the helpful type we’ve co-evolved with — they’re much more likely to be the type we’ve only had to deal with since the creation of higher density living and rapid long distance travel. Therefore air filters are likely to help children’s health both short and long term.

The immune system isn't a muscle.

Dwight, is that you?

"sick days reduced by a third" does not seem to be a level of reduction that could induce a problematic rebound.

They might have a point. Only anecdotes, but I hear that kids born during Covid (and therefore confinement) get a lot sicker than other generations.

Your experience?

Hardly anyone even thinks about peanut allergies in a nation of 1.4 billion people (India) and kids don't drop dead like flies here.

But sure, let's just call the hygiene hypothesis tenuous.

From the linked article:

"Almost no virus is protective against allergic disease or other immune diseases. In fact, infections with viruses mostly either contribute to the development of those diseases or worsen them.

The opposite is true of bacteria. There are good bacteria and there are bad bacteria. The good bacteria we call commensals. Our bodies actually have more bacterial cells than human cells. What we’ve learned over the years is that the association with family life and the environment probably has more to do with the microbiome. So one thing I would say is sanitizing every surface in your home to an extreme is probably not a good thing. Our research team showed in animals that sterile environments don’t allow the immune system to develop at all. We don’t want that."

Like your article states, there’s some evidence for exposure to benign microbes reducing allergies, but that is completely different than pathogens strengthening the immune system. Unfortunately some people seem to have remembered the hygiene hypothesis as meaning that microbes of all kinds are actually good.

There’s also a concept of immunity debt, although that’s more of an explanation for certain diseases being especially bad the year following COVID restrictions than an argument for exposure.

I suspect it's probably better to shift the sick days earlier in life. We probably can't significantly reduce the total. There are hundreds of endemic upper respiratory viruses and we all eventually get infected with most of them. It's just a matter of time. Our immune systems generally degrade as we age, so over the long run it's probably better to get infected when we're younger so that we can build immunity that protects us when we're older.

Nuance: They're still getting exposed and thus gaining immunity with the environmental filtering, just not so much viral load as to be out of school [as often].

It's a win-win from that perspective and dismissing that serves no one in the end.

It’s a good question. Obviously infinite sick is not desirable. If it were possible to induce antibodies via e.g. broad spectrum vaccinations would we see less sick kids in total?

After all the merits are supposedly eventual conferred immunity, not physically being ill. No reason to think you need to be sick to benefit.

air purification

«Air purification» interpreted as "destroying all life in the air you breathe"? That would be an extraordinary claim and you would have to prove that it is a good idea.

("Air purification" can be interpreted to be about chemical and mechanical qualities, before the consideration of the living entities in the air.)

There were doctors and surgeons against the concept of handwashing, too, but fortunately they lost.

Did the thinking go something like "Every pathogen that does not kill our patients only makes them stronger"?

  >fortunately they lost

https://www.sciencedirect.com/science/article/abs/pii/S18788...

https://www.npr.org/sections/health-shots/2015/01/12/3756639...

Lots of places are going to do the regulatory minimum for ventilation, and I sure haven't seen any much change to regulations.

We want to destroy microbes (and viruses) in specific contexts, not indiscriminately.

Apart from the known useful ones, like gut flora: no, we really do want to destroy them indiscriminantly. We bleach surfaces to do this, we can bleach air too.

Is there research that shows this? Should be incredibly easy to prove given a large percentage of the world consistently masked and another large percentage of the world consistently did not mask.

For reference, I live in a country that had one of the highest masking rates in the world (probably top 10), and this does not seem to be an issue here whatsoever. Not a single time I've heard it mentioned, and given just how huge the focus on child development is here, there's no way it wouldn't be a massive topic.

not true https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9637007/

Kids of daycare age probably can't wear masks effectively enough to make a difference, and if they can, it's not obvious that it's worth the effort.

Adults could probably reduce how many colds they get by wearing masks everywhere, but most people don't think it's worth the effort.

I looked into implementing this once. Some surprising things I learned:

1. You need UV-C (typically 222 nm), not just any old UV bulb off Alibaba/Wish/Amazon.

2. You need an extremely high UV light intensity to kill viruses if the air is just flowing past the bulb (vs shining UV on a coil to prevent bacterial/fungal growth, which is the typical usage), and you need more intensity the faster the air is flowing. Usually this requires multiple bulbs.

3. You need to replace your UV-C bulbs every 1,000 hours or so, because they rapidly lose intensity with operating time.

Just putting a "black light poster" bulb in your ducts won't accomplish anything, other than perhaps giving you a false sense of security.

You can use UV to sanitize water to drink? Must be better tasting than those gross iodine tablets!

Hmm, I wonder how effective that would be. My small home's ventilation system is currently taking in about 100m³ of fresh air per hour. That's about 1600L/minute. Let's assume the intake duct is about 20cm in diameter, and assume we can place a bulb to illuminate a 50cm stretch of pipe. That's a volume of about 16 liters. So the air would be in visible range of the bulb for about half a second. Would that be enough for a UV bulb to do anything?

This was back of napkin maths, could be way off.

Edit: sanitizing incoming air is probably pretty useless, as the outdoor concentration of pathogens is likely very low to begin with.

If you have an appropriately sized filter holder, I would just install a MERV 13 or 16 filter. They’re very cost effective, widely available, and they will remove non-living crud, too.

The main problem is that many central air systems use crappy thin filter holders. A good low-resistance filter needs a lot of area, and a 4” or 5” thick format works well, 2” is marginal, and 1” sucks. A good filter holder costs under $200, takes very little effort to install in a new system, and is an incredible pain to retrofit into an existing system. And good filters are essentially unsupported in ductless systems.

Unless you live in a place with very cheap electricity, you'll save money in the long run by getting a purpose built air purifier

Yup. We have several of these running. Helps with allergies and when one of us got COVID the rest did not.

https://en.wikipedia.org/wiki/Corsi%E2%80%93Rosenthal_Box

You're right but it won't help in my case. I created an ad-hoc system that does the same thing but the source is not at ground level. Through some form of convection I suspect around the chimney the gas is being pushed into the attic and then coming down in rooms they did not join the wall to the ceiling correctly. Most of the radioactive dust is being produced in the attic which nobody has touched for 60+ years. If I put the geiger counter in the attic it goes nuts. I'm just going to level this place and build something correctly.

Results showed increasing the CO2 concentration to just 800 ppm, a level identified as well ventilated, resulted in an increase in viral aerostability. After 40 minutes, when compared to clean air, around 10 times as much virus remained infectious when the air has a CO2 concentration similar to that of a crowded room (3,000 ppm).

Dr Haddrell said: “This relationship sheds important light on why super spreader events may occur under certain conditions. The high pH of exhaled droplets containing the SARS-CoV-2 virus is likely a major driver of the loss of infectiousness. CO2 behaves as an acid when it interacts with droplets. This causes the pH of the droplets to become less alkaline, resulting in the virus within them being inactivated at a slower rate.

https://www.bristol.ac.uk/cabot/news/2024/virus.html

Ambient carbon dioxide concentration correlates with SARS-CoV-2 aerostability and infection risk

https://www.nature.com/articles/s41467-024-47777-5

CO2 in terms of illness is merely a proxy for good air movement and exposure to the outside environment. It has its own impact on mental capacities of course.

I have never seen a evidence that CO2 is a casual agent of disease (extremely obvious exceptions excluded)

I think using a HEPA air purifier can still be beneficial. ERV and HRV typically have standard filters that may not capture very fine particles, allergens, or airborne pathogens as effectively as HEPA filters do.

Probably depends more on the air changes per hour. You'd have to compare running a filter in your room/house and the air changes it'd go through in an hour compared to your ERV/HRV. My bet is that an ERV is better if they're the same. But, it is much easier to add capacity to individual rooms with a standalone air filter than it is to change your ERV to be higher output.

Maybe.

I have a “decent” ERV. The manufacturer claims that it’s great against air pollution, wildfire smoke, etc, and those claims do not come with numbers. Empirically (as measured by an actual particle counter), it’s crap. It does have real numbers for ventilation rate, and it works great for ventilation. This is a high end ERV, and I see no evidence that any other model is better. And it can’t be: a good, energy efficient filter is large, and all the manufacturers want their devices to be small.

My solution: put a great honking filter in front of it. This increases the lifetime of its crap internal supply filter to effectively infinity (or I could remove it), adds basically no resistance, and reduces supply particulates to effectively zero.

“Great honking” here means a 24"x24"x12" “nominal” HEPA filter with a MERV 8 prefilter. The prefilter costs basically nothing. I expect the HEPA filter to last for years. I would have preferred a not-quite-HEPA 99.5% or 99.9% filter instead, but those are surprisingly hard to buy. Big HEPA filters are easy to buy. Two big MERV 16 filters in series would do the trick, too.

(The filter efficiency math is entirely different for a ventilation system than for a recirculating filter. For recirculation, MERV 13 is fine and MERV 16 is a bit better. For once—and-done ventilation, you want to reduce outdoor crap to your preferred levels in a single pass, and MERV 13 is not even close to good enough in places with pollution or smoke issues.)

Coversely, a poorly filtered fresh air system is fine for reducing air contaminants from indoors but will actively fight against a standalone air purifier if your goal is to reduce outdoor pollutants.

I totally felt that!

My kids almost never got sick in daycare (1-2 days per year), but especially the first year I felt like I had a cold most of the time. But it improved later years.

And reducing the productivity loss associated with parental responsibilities could benefit everybody!

An unpopular opinion: one of the parents is a full time care giver.

I was a kid in daycare a lot. Also, my mom (sole caregiver, besides daycare) was a registered nurse and at the time specialized in staff (i.e, direct patient care) nursing.

No way was she sick 90% of the time, or even 10% of the time, despite the numerous alleged opportunities for infection ("daycare", staff nursing, etc).

Yes. Those problems seem relatively easy to fix compared to the immense benefit of a significant reduction in disease transmission across the board.

The bulbs only last maybe 1000 hours as well which combined with their price narrows their usage.

254nm is used as part of GUV and it's not good for people and black out blinds are used in hospitals where they are installed when sanitising. Far UV 222nm is not damaging to humans that we know of but it's a peak of destruction for viruses, bacteria and fungus.

They're referring to free school lunches. That is, a lunch, at school, which is free. In the sense that it does not have to be paid for on the spot or by the child or family on account. i.e. part of the educational provision itself.

(carefully phrased to avoid "no free lunch" nonsense)

Wow. That paper made no effort to even contemplate whether the improvement was related to reduced particulate matter or to reduced organic gasses. The filters were installed in response to a gas leak — one would imagine they were carbon filters.

Sadly, the literature on the effect of gas concentrations on human intellectual function is incredibly muddy.

What evidence is there that it’s possible to “exercise” an immune system?

Getting sick to stay healthy. Makes sense to me. Now will you be exposing yourself to zika virus or HIV? Seems like those would exercise your immune system quite a bit.

Without much thought regarding cost. Calm down lol

What recent experience? Do you mean keeping them home from school for covid? I don't think the knock on effects from that are remotely traceable to their immune systems.

As mentioned elsewhere in the thread, one can be exposed (and have an immune response) to a viral load below what's normally considered symptomatic. Then the immune system learns, but doesn't have to go into over-drive which taxes the rest of the body more destructively.

In other words: Filtering part of it from the air can make exposure more like vaccination than full blown infection, which is great.

What do you think about vaccines?

Why does it run on demand? Mine runs 24/7, though it ramps down to lower speeds at night or when I'm away.

Probably a matter of cost. E.g. in some territories plexiglass screens were put everywhere between clerks and customers - as a measure that was considered more easily mandated and done (basically, simply cheaper) than modifying air treatment infrastructure.

Yes. Lots of new results in this topic. Get outside and exercise those eyes.

Box fans are noisy and in my experience fail early when running constantly. When their bearings fail they can atomize the grease.

I have one of these set up on each floor of my two story house to cut down on particulates from dust, pets, and cooking. If they also help protect from disease that’s just icing in the cake.

Proper ventilation systems address that issue