Thread by @contrarian4data

1/n

I will be discussing this paper (along with a recent contribution) in an upcoming thread, but it highlights the importance of system level thinking over analyzing an intervention in isolation:

ncbi.nlm.nih.gov/pmc/articles/P…

2/n

"In Hong Kong and Bangkok during 2008–2011, large randomized controlled trials were conducted to investigate the efficacy of surgical face masks and enhanced hand hygiene in reducing transmission of influenza in households."

3/n

"[Influenza A is believed to spread via contact, large droplets and aerosols, but the relative importance of each of these modes of transmission is unclear. Volunteer studies suggest that infections via aerosol transmission may have a higher risk of febrile illness.]"

4/n

"[using data from randomized controlled trials of hand hygiene and surgical face masks in Hong Kong and Bangkok households, inferences are drawn on the relative importance of modes of transmission and clinical presentation of secondary infections resulting from the mode]".

5/n

"[Inference on data from two randomized controlled trials of surgical masks and hand hygiene, in Hong Kong and Bangkok, found that aerosol transmission accounted for approximately half of all transmission events.]"

6/n

"[This implies that measures to reduce transmission by contact or large droplets (i.e., hand hygiene and surgical masks) may not be sufficient to control influenza A virus transmission in households.]"

7/n

"There was no statistically significant difference in the risk of confirmed influenza A virus infections in household contacts, and initial reports of those studies concluded that these interventions could have had at most a small effect on overall transmission."

8/n

So far, this is moderately interesting and consistent with pre-2020 "science".

Here's where it gets interesting:

"[In both studies, household contacts had slightly higher but non-significant risks of fever plus cough in the intervention arms compared to the controls]"

9/n

"However, when the cumulative incidence of confirmed influenza infections were plotted for household contacts, we identified a change in the risk of fever plus cough that was particularly apparent in the households in Bangkok."

10/n

So aerosol exposure may lead to more severe illness as the minimum infectious dose is reduced in aerosol transmission:

pubmed.ncbi.nlm.nih.gov/5918954/

pubmed.ncbi.nlm.nih.gov/479857/

Nasal inoculation (droplets) " manifested milder illness and significantly shorter duration of cough."

11/n

"[This is consistent w/ our hypothesis that hand hygiene and face mask interventions reduced contact and droplet transmission, increasing share of aerosol transmission which led to an increased risk of fever plus cough among the confirmed infections in household contacts]".

11/n

What if by blocking droplet mediated inoculation and subsequent generation of immunity with milder illness, universal community masking increases higher virulence aerosol exposure?

12/n

With the best of intentions, did we increase disease severity while NPIs/closures limited disease spread in low risk populations?

ijidonline.com/article/S1201-…

13/n

We know children don't generate aerosols as effectively as adults:

pnas.org/content/118/8/…

Maybe exposure to infected children with mild disease keeps the minimal infectious dose low while still creating an immunogenic infection?

14/n

Meta-point: when we intervene and do not adjust to ecological data and RWE, we may betray our best intentions.

"Don't just do something, stand there!"

@EWoodhouse7 @kerpen @justin_hart @Hold2LLC @districtai @covidtweets @ID_ethics @davidzweig

And the inimitable @Emily_Burns_V

And @ianmSC + @The_OtherET who have been hammering away on regional case comparisons for a year.