Thread by @DearPandemic

1/Q: Did getting exposed to fewer germs for the last 2 years weaken our immune systems?

We've been hearing this question a lot.
dearpandemic.org/fewer-germ-exp…

2/ Not likely. If your kids are suddenly getting sick a lot, this is likely due to “catching up” on exposures rather than a weakened immune system.

3/ Many families w/ young kids have been hunkered down for the better part of 2 years– a good % of a young child’s entire life. While isolation had *many* downsides, we can agree that not having to suction snot out of infant noses or clean up norovirus puke was a happy upside.

4/ Developing immune systems constantly “sample” microbes from the environment to learn what’s friendly or not, & there are plenty of those to be found in within our interactions with family, pets, and the natural environment (let them eat dirt!).
#microbiome

5/ While it may seem that developing immune systems “needs” lots of infections to learn, in truth we evolved in small groups of humans, not crowds. Most infections we are familiar w/ evolved much later as “crowd” infections when people started gathering in more dense settlements.

6/ We don’t *need* exposure to these infections to develop our immune systems– in fact we’ve been much better off in the last 100 years as we’ve lowered the burden of infections through vaccination & improved sanitation (no one’s missing measles, smallpox, or TB, am I right?

7/ W/ COVID-19 precautions, flu dropped to almost zero. Asthma admissions also went down dramatically, likely due to avoidance of common respiratory infections as triggers. This suggests there are real benefits to avoiding infections w/ common pathogens.
theatlantic.com/health/archive…

8/ But why do kids now seem constantly sick? We may have forgotten just how often kids were sick pre-COVID, w/ an estimated 6-8 respiratory infections/ year on average. Runny noses, pink eye, strange rashes, & stomach bugs are all familiar signposts along the parenting gauntlet.

9/ There is some evidence that kids who get more infections in daycare get fewer in elementary school. But the total # of infections is similar, suggesting non-daycare kids are catching up on exposures rather than suffering from a “weak” immune system. livescience.com/9098-kids-day-…?

10/ The total number of infections is not different, just the timing. This is likely what’s happening now–we are playing catch-up from the previous two years as we resume social contact.

11/ As w/ SARS-CoV-2, if you can avoid infection w/ common respiratory or GI infections, this is all for the good. Infections may help educate our immune system by building memory, but this is like learning a stove is hot by getting burned rather than someone warning you.

12/ Vaccines & prevention measures protect us against nasty illnesses without paying the high price of infection.

13/ BOTTOM LINE:
We “need” most infectious pathogens….like we need a hole in the head. Humans have no inherent need for exposure to smallpox, cholera, measles, polio, etc, and this is also true of less severe but common respiratory infections.

14/ The human immune system needs plenty of exposure to friendly microbes in the natural environment to help educate the immune system. So let your kids get outside, garden and play in the dirt.

15/ If you haven’t been sick the last 2 years & are now playing catch-up, hang in there. There is no magic for boosting your immunity—stick to the basics of good nutrition, sleep, & lowering stress. Your immune system is still looking out for you!

16/ For more on this topic, read @CaroMT writing for @ScaryMommy: scarymommy.com/lifestyle/why-…

17/ A great thread covering some related science from @Voices4Vaccines:

https://twitter.com/Voices4Vaccines/status/1517220510978949123

18/ Overview of the need for friendly microbes & the state of the "hygiene hypothesis: pnas.org/doi/10.1073/pn…