TRANSMISSION routes - a PROPOSAL. Have seen all the discussion on aerosol spread of a pathogen (defined as small particles that can linger in air & ventilation most important) vs droplet spread (larger particles with gobs of spit, distance important) and I propose new definition
Which is to define a pathogen (e.g. SARS-CoV-2, TB, etc.) by the best way to keep people safe, best strategies for mitigation instead. We proposed a complementary 3-way non-pharmaceutical (NPI) triangle in this @TheLancetInfDis article.
thelancet.com/journals/lanin…
Masks, distancing, ventilation being most important NPI strategies but relative importance of each being defined by (traditionally) aerosol vs droplet. Why not instead of define each pathogen by relative importance of mitigation strategies? For instance, ventilation important
for TB & SARS-CoV-2 because both can have very small particles which dissipate readily in outside air (heat, humidity also matter). However, "dogma" says that TB can only be blocked by N95 masks although this study shows us surgical face masks on MDR TB
atsjournals.org/doi/full/10.11…
patients (when outside air piped to guinea pigs) protected those guinea pigs (even when MDR TB patients just wearing surgical not N95 masks). So, this distinction is not always clear cut. And @linseymarr and I show in an article from November, along with @CDCgov in February, that
a surgical mask + cloth mask OR a cloth mask with a filter pocket inside it worked ~as well as an N95. So, why not instead define - of the 3 most important mitigation procedures for a respiratory pathogen (masks, distancing, ventilation), which one tugs
cell.com/med/pdf/S2666-…
for #COVID19, the data on outside transmission is very clear. So, outside - no masks unless closely packed together in which case some droplet spread can occur. Inside, masks (until we get to certain vaccination rate - 70% 1st dose + 1.8/100K cases or whatever metric chosen) &
a corner of the NPI triangle in the right direction. So, for instance, if ventilated (outside, window open), no masks for mitigation but inside needs masks for mitigation (until we get to 70% 1st dose vax rate + 1.8/100K cases as possible metric to stop masking indoors).
This is possible framework to bring us all together on definitions of mitigation strategies & relative importance of each vs defining by aerosol vs droplet as non-continuum; welcome thought paper on this with someone after Aug. Speaking of, going off twitter until Sat to work.
And, importantly, if you look at our NPI triangle, the susceptibility of the host is inside the triangle. This is why the WHO does not advocate for masking young children & neither should we. Everything becomes individualized mitigation instead of @onesizefitsall
Quoted in this well-done @medpagetoday article describing these distinctions between droplet & aerosol and how think we should go towards a mitigation strategy approach instead of a "size of particle" approach.
medpagetoday.com/special-report…

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More from @MonicaGandhi9

13 May
This JID study was the one quoted by CDC as saying risk of outdoor transmission was 10%. However, corresponding author clarifies risk much much less than that based on review of the literature. Moreover,
there have been two additional examinations of the question not included in this review which is this report from Ireland examining >232,000 infections & finding 1/1000 linked to outside. irishtimes.com/news/ireland/i…
And this scoping review from University of Canterbury concluding that outdoor transmission very rare, citing opportunity costs of not encouraging public to congregate outdoors
canterbury.ac.uk/science-engine…
Read 4 tweets
11 May
An Open Letter to the Biden Administration and Congress from multiple public health/global health academic leaders in US on "Ensuring Global Health Security via Vaccine Donation" regarding humanitarian crisis in India
hividgm.ucsf.edu/ensuring-globa…
"Second year of the COVID-19 pandemic showcasing the stark inequity in global health security. The most advanced economies are entering a period of containment while the rest of the world is unable to respond or recover from the pandemic with relevant medical or economic tools"
"U.S. is on track to a summer of pre-pandemic levels of normalcy while South Asia and India in particular is reporting an estimated 1–2 million cases/day and 15,000-25,000 deaths/day. The pandemic will end when it ends for all.". Even with US vaccinating 12-15 yo, 70 million
Read 9 tweets
11 May
I see a lot of concern on Twitter today about #B.1.617 variant evading immune response. I think it is likely more transmissible and hospitalizations and deaths increase if cases increase which is happening in India and is tragic.
However, t think B.1.617 will evade immunity from the two vaccines in India - Covaxin & AZ (nor the vaccines you have in UK - Pfizer, AZ, Moderna): This study on the #Covaxin vaccine (Bharat pharm) shows strong neutralizing Ab titers against B.1.617
biorxiv.org/content/10.110…
Moreover, and this is a KEY point, if T cells decrease our severity of disease to an infection (references here- will break them all down when have more time), what is our T cell response against the spike protein with AZ vaccine- COMPLEX and in breadth. How do we know that? Image
Read 7 tweets
8 May
7 reasons why think immunity to COVID from vaccination or infection will be long-lived (and why I continue to marvel that CEOs of companies who stand to make profit from boosters get to message that boosters needed; instead, please donate vax to India).
1. Memory B cells: Image
We discussed this at more length before; remember this amazing memory B cell paper that showed us that 32 people ages 91-101 who survived 1918 flu pandemic STILL had memory B cells that could produce neutralizing antibodies to that strain 9 decades later
nature.com/articles/natur…
Memory B cells last long time & hang out in germinal centers (like lymph node) until they are needed again and then come out to produce neutralizing antibodies against the pathogen. Do we know COVID-19 vaccines produce memory B cells? Yes from this paper
researchsquare.com/article/rs-310…
Read 17 tweets
8 May
Wanted to tweet on masking as getting a lot of interest in this today (I am not a ventilation scientist; I am just an epidemiologist/ID doctor who can see from epidemiology studies how low risk outdoor transmission is). #1, Indoor masking is important when case rates high; wrote
many papers on this over the pandemic including with experts like @linseymarr. But study after study showing how low risk of outside transmission is which led to CDC recommendation of not masking outdoors when vax & many experts to not mask outside at all unless in large crowd.
Those studied summarized by multiple people in multiple threads & we summarized some in this WSJ article below which is why so many now calling on @CDC to remove mask requirements for unvaccinated children outdoors.
wsj.com/articles/take-…
Read 7 tweets
7 May
Good news from #HHS: we are at the LOWEST THREAT LEVEL in the US that we have ever been in the entirety of the pandemic, when looking at cases + positivity rate + inpatient + ICU together (#vaccineswork). Taking each at time:
healthdata.gov/Health/COVID-1…
-Test positivity: Last 7 days test positivity rate is lowest it has been during the pandemic: 4.0% (Light Green)
-Cases: 97 cases per 100k for the Last 7 Days down -11% from previous 7 days (Orange)
-Inpatients with COVID-19: At 5% (Light Green)
-ICU for COVID: 11% (Yellow)
.
Still only 3 states outside of the Light Green or Dark Green Zone on Inpatient Beds (MI -- orange, MD, yellow, PA -- yellow). Keep following these metrics to see the pandemic recede with the increasing roll-out of vaccine & decide when public health emergency over in US
Read 4 tweets

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