Do We 'Catch' Flu? How Often?

Post #697

Back in the early 1980’s, Edgar Hope-Simpson discovered incongruity between established epidemiological principles and the spread of flu:

*NOTE: The seasonal aspect of flu indicates that the Sunshine Vitamin (vitamin D) could be the culprit.

While Hope-Simpson could not explain the incongruities satisfactorily, subsequent researchers took up the project and “completed the mission” — explaining why flu spread is so odd. To cut to the chase, flu transmission dynamics are thought to be dominated by two factors:

1. “better spreaders”

2. vitamin D

If a small minority of individuals are ‘better spreaders’ (aka, super spreaders) of flu, then the interaction of the flu virus with their particular immune system can super-charge a flu. But the vast majority of human beings cannot spread flu very well. When secondary attack rates were tracked in households, only 1% to 38% “catch” flu (left):

The circles at left show lab-confirmed (PCR) flu in household members of an index case, running from a low of 1% up to a high of 38%. But a 38-fold variation in risk of spread is not supported by common epidemiological principles. It means that we are missing something — not taking something into account when we should.

Variable vitamin D levels, interacting along with sporadic better spreaders, can explain a 38-fold difference in one’s risk of flu. A summary estimate of protection against acute respiratory infection by non-bolus Vitamin D doses in those who began deficient in active vitamin D shows that treatment with D cuts your risk in half:

Red faces were going to come down with an acute respiratory infection whether treated or not. Yellow faces would come down with one in the absence of vitamin D, but would not get sick if given vitamin D. This is the overall effect on those low in D, however, and individual effects on an individual person can be manifold (up to 38-fold).

Even when you artificially jam copies of flu virus up people’s noses — or use a flu-contaminated throat spray or an aerosol method — you can’t get everyone to make copies of flu (you cannot infect everyone, no matter how hard you try):

At bottom right, the estimate of 90% means that there are 10% of people whose bodies will simply not become infected with flu, even if you shoot it up straight their noses or right down their throats. They could be called “super stoppers.” But, in reality, they might merely be found to have had a lot of active vitamin D at the time, or something.

And of those whose bodies make copies of flu virus after being challenged with an artificial dose, up to 62% of them never get sick:

In the second row down on the far right, the 38.4% value means that 61.6% of people who had been artificially infected with flu don’t get upper respiratory tract symptoms. To recap, the indication is that 10% of human bodies “never” get infected with flu, and of the 90% who can get infected with flu, up to 62% of them “never” get sick from it.

So it seems that it is possible to catch flu, but two things might be required in order for you to catch flu

1. exposure to a ‘better spreader’

2. low vitamin D

Reference

[incongruities in flu dynamics cannot be explained by conventional thinking] — Hope-Simpson RE. The role of season in the epidemiology of influenza. J Hyg (Lond). 1981 Feb;86(1):35-47. doi: 10.1017/s0022172400068728. PMID: 7462597; PMCID: PMC2134066. https://pubmed.ncbi.nlm.nih.gov/7462597/

[better spreaders and low D status explain flu dynamics] — Cannell JJ, Zasloff M, Garland CF, Scragg R, Giovannucci E. On the epidemiology of influenza. Virol J. 2008 Feb 25;5:29. doi: 10.1186/1743-422X-5-29. PMID: 18298852; PMCID: PMC2279112. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2279112/

[a 38-fold variation in risk of secondary infections exists in households] — Tsang TK, Lau LLH, Cauchemez S, Cowling BJ. Household Transmission of Influenza Virus. Trends Microbiol. 2016 Feb;24(2):123-133. doi: 10.1016/j.tim.2015.10.012. Epub 2015 Nov 21. PMID: 26612500; PMCID: PMC4733423. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4733423/

[if low in vitamin D, then non-bolus doses of D cut your risk in half] — Vitamin D supplementation to prevent acute respiratory infections: individual participant data meta-analysis. https://www.ncbi.nlm.nih.gov/books/NBK536323/

[artificial infections only take hold in 9 of 10 people, and only 3 or 4 out of 10 get sick from them] — Carrat F, Vergu E, Ferguson NM, Lemaitre M, Cauchemez S, Leach S, Valleron AJ. Time lines of infection and disease in human influenza: a review of volunteer challenge studies. Am J Epidemiol. 2008 Apr 1;167(7):775-85. doi: 10.1093/aje/kwm375. Epub 2008 Jan 29. PMID: 18230677. https://academic.oup.com/aje/article/167/7/775/83777?login=false