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Comment by gojomo | Hacker News Reader

To some extent, the circulation of natural flu cases, of routine non-severe varieties, serves as a natural 'booster' refreshing immunity against related strains.

For example, every once in a while, a new flu strain hits a certain younger or middle-aged cohort much harder than usual, because some other strain decades ago left lingering immunity in yet-older people. Examples:

2014 flu season: https://www.fredhutch.org/en/news/center-news/2014/10/flu-hi...

1977-78 Russian flu: https://en.wikipedia.org/wiki/Influenza_A_virus_subtype_H1N1...

As a result, this season of abnormally-low flu infections may not be unvarnished good news. When normal interaction levels recur, we may see a rebound of flu cases – in numbers & severity – from all the people who didn't get a typical mild seasonal re-exposure. Decades from now, people may suffer for having missed a survivable-exposure-while-young. Time will tell.

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one can wonder what other antigens we decreased the exposure to with the resulting immune system changes like decreased diversity and levels of antibodies present - i mean it may be kind of similar to the effect of living in highly antimicrobal environment which results in weaker immune system with all the allergies and autoimmunes as a result down the road. Even super-healthy people like astronauts have immune system weakening and hypersensitivites developed as result of decreased exposure to diverse antigens:

https://www.sciencedaily.com/releases/2019/01/190123174405.h...

"Scientists compared blood samples of eight crewmembers who completed missions to the International Space Station with healthy individuals who remained on Earth. Blood samples were taken before launch, at several points during the mission and after the astronauts' return to Earth.

The results showed that NK-cell function is impaired in astronauts as compared with pre-flight levels and ground-based controls. At flight day 90, NK-cell cytotoxic activity against leukemia cells in vitro was reduced by approximately 50 percent in International Space Station crew members."

> as result of decreased exposure to diverse antigens:

The link you posted doesn't make that claim. The word antigen doesn't even appear in the article you linked.

Rather, it claims:

"In order to do that, you have to first figure out what's causing the decline: Is it stress? Is it microgravity? Is it radiation? Is it a plethora of things? When we figure that out, we can try to find ways to directly target those factors and mitigate them."

Having said that, we know for a fact humans can't survive long term in a completely sterile environment as babies wouldn't have their integumentary system and digestive systems populated with commensal organisms shortly after birth in a completely sterile environment.

So it's seems at least plausible to me that living in a increasingly sterile environments is likely to be a net negative on overall health etc etc.

Right, that article doesn't. I saw several articles which do mention it, for example https://www.statnews.com/2019/02/15/scott-kelly-nasa-twins-s...

"Immune issues sound familiar to Dr. Jerry Linenger, an American astronaut who spent more than four months on the Russian space station Mir. He said he was never sick in orbit, but once he came back to Earth “I was probably more sick than I was in my life.”

Astronauts launch into orbit with their own germs and get exposed to their crewmates’ germs and then after a week with nothing else new in the “very sterile environment” of a space station “your immune system is really not challenged,” Linenger said."

Thus we can see that not being sick while in orbit, despite all the stress and other space factors - microgravity/radiation/etc. - which are supposed to weaken immune system, while getting sick on return when those space factors disappear clearly favors the immune system antigen exposure dependence explanation.

Thanks for the response.

Yeah, I can see why having astronauts not get ill in space makes sense at the moment, and that for more long-term viability of living in space humans are going to probably have to take their mess and germs with them.

And also that lack of exposure to immune-challenges probably represents a net-negative effect on our well-being in this life and also reduced selection-pressure in the evolutionary sense.

Quite concerning!

I wonder how that would compare to other extremely isolated groups, such as Antarctic researchers during the winter months. With the ISS, there is a large confounding factor in the lack of gravity, making it hard to tell which effects are from isolation.

The immune system is still not well understood. Vaccinations have certainly changed the course in a few ways. I've always found the story of the pertussis vaccine interesting: https://i.imgur.com/v8e8trm.png For one, it's a "vaccine" not against a virus, but a bacteria. More specifically, a toxin produced by the bacteria. Those that have been vaccinated are immune to the toxin, not necessarily the bacteria. So prior to 1950, most people that got whooping cough were around the age of 5. Now the only ones that get whooping cough are infants or the elderly.

Another example is the 1920 pandemic, where the weirdly high mortality in young adults prompted theories that the dominant strains of influenza changed around 1890, and people born after that would be naive for H1N1. There've been some interesting calls for tailoring seasonal flu vaccines not just for currently or expected circulating strains, but for the age of the recipient.

Maybe I'm misreading the article (or your post), but isn't that first article saying exactly the opposite?

> When someone is infected with a virus they’ve seen before, the immune system tends to pump out antibodies created during the first infection. That immune memory normally helps fight off secondary infections faster, but that memory can occasionally backfire if the virus has mutated in the right way to evade those original antibodies – as happened with last year’s flu.

i.e. youth exposure to a particular 70s/80s strain of the flu virus actually worsened the immune response in 2014?

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