> 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

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.

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.

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.

There's no blanket "best time" to get sick with an infectious disease. And some diseases, like chickenpox, later surface as painful shingles (which in the worst case can result in permanent nerve damage).

The best thing to do is vaccination. It's safe for the vast majority of the population and sidesteps complications completely. Get your flu shot.

Heck, I think what makes a programmer good is something that can easily get in the way of fields like medicine. Good programmers like to create abstractions to put things into neat boxes. Programming is an exercise in generalization and specialization and, unfortunately, that can drive people to thinking "Oh, these diseases are alike so lets put them in the same box". That particularly gets in the way because MOST people won't experience complications from illness. Consider measles blindness, 30 million people get measles a year, 60,000 will get blindness. That's a 0.2% chance of developing blindness as a result of measles (1 in 500). That can lead to unfounded skepticism because your observed reality "I don't know anyone that's been blinded by measles!" might make you think that the risks are lower than they are.

And, heck, as a programmer if you have a method that fails at 1 in 500 cases you might even be justified in punting fixing that thing.

I don’t necessarily disagree, but if I intentionally ignored a fix to a method that resulted in a service-level equivalent of a user going blind every 1 in 500 times it ran, I’d get fired pretty quickly. But then again, I have also met many programmers who, when presented with such cases, pretend they do not exist.

The results aren't in yet, and of course will be subject to reproduction/duplicatation, but I suspect that's what we're seeing here. People (children) are still getting sick, just less so, presumably because they're getting exposed to lower concentrations of pathogens. The article doesn't make it clear (or I missed it) if the reduction is in severity (time spent recovering from being sick), frequency (number of times one gets sick), or a combination thereof. If I'm right, I'd expect it to be a reduction stemming from both reduced frequency/severity.

Some days the kids are just a bit off, and taking their temperature shows slightly elevated temperature (37.2°C in ear). I'm pretty sure they are fighting some mild infection, but they aren't really ill.

And then, measles in particular can actually damage existing immunity to other infections, making exposure to it quite a lot more dangerous than just the immediate infection. https://asm.org/articles/2019/may/measles-and-immune-amnesia

Think about - immune system evolved over millions of years, is it plausible that it needed wild tribes of hunter gatherers to huddle in a nearly airtight box for 8 hours and infect each other to work

The macrophage then hands over some of the important pieces to undifferentiated T cells. Those T cells then "differentiate" into one of two forms.

The first are "Helper T cells" which carry the "design" for antibodies (immunoglobulins, i.e. proteins that bind to pathogens directly. These then share those antibody designs with B-Cells.

The other type are "Killer T cells" which carry the "design" for T-cell-receptors that can detect "sick" cells for this specific pathogen or defect. They go hunt after the specific cell and essentially cause them to explode with the power of hydrogen peroxide. Then the macrophages eat up the dead infected cell and all the pathogens inside it and start the process anew.

Now those B-Cells get the "design" for antibodies from the helper T cells and differentiate into two types.

The first is essentially a factory that mass produces the antibodies and dumps them into the body. Those antibody proteins then bind to the pathogens and the macrophages can then directly attack the pathogens (because they have a bunch of big flags/alarms on them).

The other type of B-Cell that they can differentiate into are memory B-cells. These keep the designs stored inside them and keep detectors for the pathogen on their cell membrane. Then they "go to sleep" until their detectors are activated by the pathogen. They live out their lives and replicate as needed to continue their lineage. When a pathogen shows up, they bind to either the pathogen directly or to some of the proteins it produces and they turn their factories on at full speed and start mass producing antibodies to start the immune response as fast as possible locally before the pathogen can do damage. They get depleted in this effort of course but if things go okay, the following immune response should trigger the creation of more memory B cells. (and when they don't you get stuff like immune amnesia).

There are also "memory T-cells" but how they come about and how exactly they work is fuzzy and not super well understood. It's similar to memory B-cells but it's way more complicated and a bit "magic".

But yeah eventually then your body beats the infection and things go back to normal with the memory cells hanging out in the body.

Now the important thing with intensity of infection is that a mild infection will generally guarantee your body learns a sane, moderate response but a major infection can send your body into a panic and put the immune system into overdrive. That can train a response that attacks the pathogen but also attacks a lot of other stuff in the process (auto-immune response).

You can think of this kind of like an analog version of machine learning on proteins (the training input). A bad fit can end up mischaracterizing healthy cells and bodily structures as "pathogens" and cause long term issues or even just severe reactions when you get a reinfection.

Now for getting "trained" from the parent, this happens during pregnancy by diffusion of a subset of the antibodies from the mother to the fetus (not all types can but many do). Those stick around for a good while and eventually the child gets minor exposure to various pathogens and those shared antibodies kickstart the child's immune response enough to build up its own memory.

Hope this helps.

https://upload.wikimedia.org/wikipedia/commons/4/41/Primary_...

It’s not a good idea to confuse the impacts of vaccines and infections. Vaccines are carefully developed specifically to help the immune system. Viruses evolve to hurt it.

This is an extremely well researched and presented video that exposes the fact that HEPA purifier marketing is a bit of a scam. The most important factor in air purifiers is not the filter but Clean Air Delivery Rate. You can only make a difference if you are moving air through the filters faster than particulate is introduced into the air.

I just returned a Medify filter because their advertised square footage is way higher than what the purifier should support based on the info in the video; it is inadequate. No idea how they are calculating their numbers - not to mention it's probably at the max speed setting - but it doesn't align with the sources from the video.

On top of that, smaller air purifiers must move air faster, be noisier, and the smallest sizes of particulate are captured most effectively at low velocities.

Use something like this to make a nicer version of a CR box: https://acinfinity.com/component-cooling/cabinet-fan-systems...

Or buy one of these: https://www.cleanairkits.com/

Those seem to be the best options that ACTUALLY work.

Typically for respiratory pathogens you want to shoot for 6+ ACH, so as a very rough initial guess I often simply divide the rated area by 10.

And yes, every manufacturer only gives specs for the highest fan setting. This is misleading because typically this fan setting is very loud, so few people actually run it 24/7 (and those who do will probably suffer hearing loss).

Edit: hit reply too soon. Wanted to add: are air purifiers as effective as increased ventilation? Should we combine the two?

Also my ERV only runs on demand (~1/3 of the time, which is not enough filtration)

One of the reasons why mine also runs when I'm away is that it helps prevent mould growth in the heat/moisture exchanger, as that thing is a bit of a pain to clean.

Best thing I did for my house so far!

One of the biggest takeaways seemed to be that UV light destroys viruses in seconds.

Seems like there a lot of things we could do

My main take-away was this was very easy to screw up and cause eye damage, especially in an home setting where less care would be taken.

I might hook one up now that I have the idea.

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.

I don't think this should need to be the case. Low pressure mercury arc lamps (253.7nm) last 10,000 hours in water treatment applications - a much more palatable replacement timeline (1 year) vs every few weeks!

The short-lifetime bulbs are usually 222nm Far-UVC bulbs, which are safe for human exposure. These shouldn't be necessary to treat air as part of an enclosed HVAC system. I feel that the hype around 222nm / "safe" UVC has done a disservice to just using "dirty" 253nm UVC, which kills everything just as well as long as you keep people from being able to look at it.

Even replacing bulbs every 1 year seems like a lot more than people are bargaining for. Most people seem to expect UV will be a "Set It And Forget It" solution (hence why they prefer it over filters), so they risk neglecting the necessary replacement interval.

Could you put a long tube-shaped 222-UV bulb inside a larger tube with a UV-reflective coating inside to enhance the efficiency?

... And, can UV bulbs be mirrored, so they reflect as well?

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.

I’ve seen some claims that it can destroy viruses on some medium. Imagine a filter in the light catching virus particles or particles that have viruses. The light destroys them while they’re stuck in place. I would need some independent testing to verify that claim.

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.

If you dip a Nalgene bottle to fill it, then purify the contents, you would typically then bleed the threads by holding the bottle upside down and loosening the cap.

With chemical treatment, the iodine in the water works to neutralize any pathogens that aren't flushed out of the threads. If you've used UV, you're kind of hoping that the flushing action has physically washed out anything lingering in the threads.

Anecdotally, people using UV get more cases of waterborne illness, but I don't know if anyone has rigorously studied this. Hikers are naturally resistant to controlled experiments.

If you don't like the flavor of iodine tablets, I recommend AquaMira instead.

Source: AT ME-MA 2003, GA-ME 2010. UV was pretty popular by 2010 and for a couple years after. Not planning a thru hike at the moment, but I believe the Sawyer squeeze filter is super popular now.

https://en.wikipedia.org/wiki/Ultraviolet_germicidal_irradia...

> UVGI for water treatment // Using UV light for disinfection of drinking water dates back to 1910 in Marseille, France. The prototype plant was shut down after a short time due to poor reliability. In 1955, UV water treatment systems were applied in Austria and Switzerland; by 1985 about 1,500 plants were employed in Europe. In 1998 it was discovered that protozoa such as cryptosporidium and giardia were more vulnerable to UV light than previously thought; this opened the way to wide-scale use of UV water treatment in North America. By 2001, over 6,000 UV water treatment plants were operating in Europe

And yes, there are also commercial products for home use.

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

Obviously impractical in many areas but it's part of the California dividend

Edit: it really is bizarre because Radon is primarily produced by reactions underground/in the earth and has a relatively short half life (3.5 days). I don’t see how it could be atmospherically sourced without it being a hazard to the whole community, regardless of the bizarre convection currents that bring it into your house. It’s unlikely to be produced in your attic.

If I were you, I’d want to know more and understand how this is all happening lest you raze and rebuild and find you still have a problem.

I would suspect fly ash as a possible source if the house ever had a coal-burning furnace. Or maybe someone had a watch-painting operation or mixed radioactive glazes or paints there. Someone with appropriate equipment could do a much better job identifying the source.

Any notion of whether it's β or ɣ radiation you're detecting?

Demolition is going to need careful monitoring to ensure you don't contaminate the entire site.

Will be neat to see if the kids were still carriers, but managed to keep the viral loads down such that they weren't "sick" during that time. I recall a study a few years back that said kids at that age were basically always sick, just not often symptomatic.

Have a few Levoit air purifiers that sit flush against the wall. But would be nice to have an extra layer at the source.

(this 󠁺󠀮message contains a hidden secret)

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

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

Here on hacker news we have a long tradition of software people claiming that some property of a tangible world, like ‘no such material physically exists’ are easy to fix.

We began partial daycare on Thursdays + Fridays in winter. Daycare is like Cancun for bacteria. Dry cold can weaken the skin, and cold is good for bacterial protein stability.

The cycle begins: kid starts incubating on Thursday. On Saturday he's sick, and you hope for a good lottery. Diarrhea? Puking? Maybe not. But a runny nose most probably. These may ruin your nights, still.

Sunday they are sick, and you begin to feel unwell. Monday the kids is recovering, but you're still in it. By Wednesday you should be good though. And then it's Thursday again.

On another topic air filtering is great for the kids I'm sure; but I can't help wonder if it's just kicking the can down the road.

I don’t know if it was that much, but when my kids were in daycare, it was definitely A LOT for sure. Work doesn’t provide nearly enough sick time for that period of being a parent. So what are parents to do if they’re not able to work from home?

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).

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.

Meanwhile, air purifiers use a bit of power (probably less of an environmental impact than the inevitable littering of masks which are basically all microplastic while looking like harmless paper), probably cost less per filter change than a week's supply of mask, and have a relatively negligible comfort impact.

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

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.

Do you have many cases of children being in homes where they have limited access to people speaking the national language? Do you talk to individuals who are directly responsible for teaching those folks the language?

While it's reasonable such an adverse effect would be stronger in cases where at home a different language is spoken than the national language, it's very unlikely that it would only have a noticeable effect for exactly those families, with zero noticeable effect otherwise. And here, where masking rates were extremely high and amount of attention put on/money spent on child development is higher than almost anywhere else in the world, no one has ever brought it up.

This doesn't even touch upon the fact that unprivileged families are much harder hit by epidemics (let alone Covid) in general, due to a host of other factors.

> But of course if the facts go against the government narrative, the “studies” will not report them.

The studies showing that masks were incredibly effective at preventing disease spread went against the US "government narrative" at the time, since I imagine you're talking about the US.

I've known multiple people who swore potatoes cured their sickness. Yes, potatoes. No, not eaten - worn.

My sample size is greater than yours. Does that mean potatoes cure illness purely by being in proximity to people? Probably not.

People are dumb and unreliable. People are fueled by beliefs. And when those beliefs are challenged, almost every time this is taken as PROOF of the belief. They are untouchable. Agree with them and that's great, disagree and you're being silenced or the government or something thereby giving validity to their belief.

Anecdotes are not meaningful data.

This is beside the point however. Both the government studies and the boots on the ground in fact agree that masking causes significant developmental disabilities, the only disagreement is the extent.

Yes, things can have a political motive. But you ALSO have political motives, you just don't know it. For example the climate change denial has a very real political motive - to protect the oil and gas industry. Oil and gas have been denying climate since the 60s, and our government backed them because of political will.

Masking, during the pandemic, saved lives. This is not up for debate. Whether it's a good idea now is another question all together.

I also agree that personal anecdotes from trusted parties are more valuable to my decision making than "data" — but those are personal anecdotes, not anecdotes from anonymous Internet personas.

We aren't your friends and we don't know you. Why should we trust you if you are vaguebooking about something that is a common conspiracy trope?

> "Utilizing the model, we used portable air cleaners in two day care units (A and B, number of children participating in the study n = 43) and compared infection incidents between the two intervention units to the rest of the units in city of Helsinki (n = 607). The intervention buildings had mechanical supply and exhaust air ventilation."

https://www.sciencedirect.com/science/article/pii/S295036202...

You also have to consider external air quality, as ventilating a building with polluted air would have negative effects like increased asthma. In that case perhaps a sealed building with air purifiers is a better option, but then CO2 buildup is a concern, so you'd need CO2 scrubbers, which are expensive.

That's why clean air regulations matter, and getting off fossil fuel combustion as an energy source (and limiting pesticide/herbicide use in agricultural zones) is the easiest route forward.

Next up:

* Air purifiers in schools cut parent's sick days too (not just "I need to care for my kid" days - "parent is sick" and "childless coworker of parent is sick" sick days)

* Air purifiers in strategic locations (high density offices, public transit, schools, ...) cut sick days across the population.

I think this will be our generations "realizing that washing your hands before surgery makes patients die less", and it's quite embarrassing that with all the knowledge about viral transmission we couldn't figure this out before the pandemic, and even more embarrassing that we couldn't figure it out immediately after we tested many of these things at a large scale.

There were doctors and surgeons against the concept of handwashing, too, but fortunately they lost. Unfortunately, it took a long time for them to lose, and a lot of people died as a result. How do we skip that part?

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

(It's also possible for a study to be flawed, but even then, the reaction should be to do better, not to react with "crazy and insulting".)

and possibly "If this were true, I'd be responsible for killing a hundred people, therefore it is not true."

> some doctors were offended at the suggestion that they should wash their hands and mocked him for it

The common thread in all of these, though, is not embracing a fundamental mindset of "If I'm wrong I want to know that and change and improve".

Not at all: perfectly serious. We are in a system surrounded by living entities - some innocuous, some threatening, some helpful, some being the threatening food of helpful ones...

Your body already hosts living entities that live with you symbiotic. Some of them have the extremely important role to keep the worse others at bay through geopolitical control (you remove them, the damaging ones have free course...).

There are many more things around you than «tapeworms and other parasites». And they could be active part of a system (which could get unbalanced without a part).

So: before stating e.g. that all other life (e.g. in the air) should be wiped out, an intellectual inquiry about the model must be given. You do not embrace what superficially sounds like a good idea.

Surely not the same thing as Semmelweis. 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.

"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."

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 mean, many populations have more/less risk of many physiological things. That's just how it goes.

Black men are at much higher risk of prostate cancer. White people of melanoma. As a man, I pretty much don't have to worry about autoimmune disorders because my risk is 1/10th that of a woman's. But, my risk of heart disease is much higher - even at the same weight!

Are the benefits of this theory meant to start appearing any time soon...?

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

Or do you just think that having a few sick days per year is better than marching into work no matter what state you're in? A very different proposition.

Considering it used to be commonplace to have 10 children and then maybe 2/3 make it to adulthood, I would say we absolutely can and have reduced the total number of sick days. We've also reduced the severity of sickness.

That's ridiculous. During the crisis times of covid, the incidences of other communicable disease dropped significantly. Plus, to be frank, this is just an idiotic suggestion with zero reasons to think there's some set number of days people are sick. Before having kids in daycare I was rarely sick. I had a child not in daycare and was never sick. Now we're sick all the time, which wouldn't happen if my wife could stay home with them or we didn't have kids.

I've had kids in daycare as well. Occasionally you get the sniffles. So what.

We can and we have. Through things such as the measles vaccine.

People forget that child mortality used to be a thing.

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

I definitely understand the teachers don’t want to be sick, and it’s a hardship on parents to keep kids home, so it’s not all about the kids’ health. But the kids’ health might be better served by letting them get more minor illnesses, not less.

And I'm willing to believe that some childhood exposure to pathogens is beneficial, but I don't think we know how much of a good thing is enough, or too much.