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Monica Gandhi MD, MPH Profile picture
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27 Jul, 7 tweets, 3 min read
Wanted to explain what @CDCgov did today in terms of masking guidelines & why I think made sense. They did not say everyone mask- they said mask according to community transmission rates + vaccination rate in your community. I, @syramadad @ashishkjha wrote
washingtonpost.com/outlook/2021/0…
this article in Washington Post a long time ago saying look at community transmission rates + vaccination rates as metrics of when to lift restrictions (we used a hospitalization metric of <5/100K because case rates can become uncoupled from hospitalizations at higher vax rates)
So, what did the CDC do today? They released this MMWR article saying just that- decide on masking on vaccination rates + community transmission rates. Why? Because we aren't where we wanted to be with vax rates in US by this time & we have the delta.
cdc.gov/mmwr/volumes/7…
And because your rate of getting even a mild breakthrough infection after vax depends on how much virus is circulating (e.g. community transmission rates). So, CDC guidance today took this into account, said mask inside when vax'd if at substantial or high transmission, I agree.
And why did CDC put in "metrics" in their masking guidelines today as we had urged in the WaPo article & also this NYT article on schools? Because threat went up with delta, will go down when delta passes & metrics on masking allow for "off ramps"
nytimes.com/2021/06/08/opi…
And we had suggested a hospitalization metric rather than a case metric because case rates noisy and may be inflated by testing asymptomatic people after vax without taking into account viral load (asymptomatic after vax + low viral load=vaccine success)
npr.org/2021/07/26/102…
1) Now that CDC has taken a metric based (rather than vax approach for masks), masks for children should follow the same metrics as those for everyone else; 2) Main focus in our vax hesitant nation should be on getting people vax'd, which is the way to turn epidemic into endemic

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More from @MonicaGandhi9

Monica Gandhi MD, MPH Profile picture
29 Jul
Good summary from WaPo on day's issues 1) waiting on CDC data on vax'd and viral load (we will likely need culture for deeper dive); 2) masks @CarlosdelRio7 "putting toothpaste back in tube"; 3) plummeting UK cases: delta-driven natural immunity+ vax
washingtonpost.com/politics/2021/…
In terms of UK cases falling despite easing lockdowns, not surprising. Delta is a hurricane- if finds vaccinated's nose, will boost immune response if asymptomatic; finds unvax'd adults FAST & tragically causes deaths or natural immunity if non-severe
cnbc.com/2021/07/28/uk-…
Of note,- I'm sure CDC has data on viral loads with delta & will tell us. Delta has higher viral load, different beast than alpha. But is a PCR-determined viral load in a vax'd person with immunity (Abs/T cells in nose) as infectious as in unvax'd? Do we need culture to tell??
Read 14 tweets
Monica Gandhi MD, MPH Profile picture
28 Jul
Bit counterintuitive to think that vaccinated people with antibody & T cell islands in their nose to transmit infection at the same rate as those who are unvaccinated. So, would be good to see data & probably need culture data to confirm not dead viral particles from vax success
However, I think it is about inoculum. If you are vax'd & have high rates of community transmission around you, more likely for virus to get in, cause a mild breakthrough as stimulate antibodies (T cells, which fight severe disease already there)
Delta variant has higher viral loads than alpha or ancestral strain so I am sure -with those higher viral loads, vaccinated people can transmit with mild breakthroughs- However, transmitting at equal rates seems counterintuitive.
Read 4 tweets
Monica Gandhi MD, MPH Profile picture
28 Jul
Spoke to @fayeflam at Bloomberg last week of how vaccine memory should be long. There are many papers on this but I wanted to give you the 4 most interesting ones in this thread in my opinion.
podcasts.apple.com/us/podcast/32-…
So, we all love this paper showing the vaccines generate memory B cells (even in the lymph nodes with biopsies) although La Jolla and other places had already shown memory B cell formation in blood in other studies
nature.com/articles/s4158…
So you have memory B cells and see a variant in the future? Even if your antibodies wane (which they will, not a glitch but natural for the immune system), you have the blueprint to make more from memory B & those antibodies will ADAPT to the variant
medrxiv.org/content/10.110…
Read 6 tweets
Monica Gandhi MD, MPH Profile picture
26 Jul
In this critical time of delta circulating, we need clean data on 1) what % admitted to hospital are unvaccinated; 2) if vaccinated, is it breakthrough or asymptomatic with universal screening; 3) if vax'd, need CT of PCR test or some way to know viral load
This article explains concept of viral load and how to determine from PCR cycle threshold (if that is the test hospital is using); rapid antigen is another test using lateral flow assay
washingtonpost.com/outlook/2021/0…
If delta higher viral loads explaining transmissibility,
1) Asymptomatic breakthrough, low viral load: You fought the virus, brought it down & vax success, can't spread
2) Symptomatic breakthrough: Need to know if viral load high enough to transmit
3) Severe breakthrough: Boost
Read 4 tweets
Monica Gandhi MD, MPH Profile picture
25 Jul
Reason viral load (VL) becomes so important now is due to delta. So much more transmissible with those studies showing higher VLs. Those vax'd may get some in nose, will strengthen your immune response to fight it off so need to know if VL stays low
washingtonpost.com/outlook/2021/0…
Then for a mild breakthrough infection after vax, is that when an antiviral like molnupiravir comes into play - best to stop viral replication early for mild disease (severe disease mediated by innate immunity which is why we use steroids)
And then severe disease of course prevented by vaccination which everyone very convinced of at this point with what we have seen from delta. So, working on getting vaccination rates up is of utmost importance as outlined well here @apoorva_nyc
nytimes.com/2021/07/25/hea…
Read 5 tweets
Monica Gandhi MD, MPH Profile picture
23 Jul
Breakthrough coronavirus cases are disappointing ― but most of them are also evidence that the shots are working. huffpost.com/entry/breakthr… via @HuffPostLife
Think this is responsible reporting by the @HuffPostLife about breakthrough infections with delta as the promise of these amazing vaccines was in the yellow column, in preventing severe disease & death, which is what the vaccines are doing. Never before in history have we swabbed
noses for asymptomatic infection; vaccine trials always designed on preventing disease. No vaccine for common cold because that is not the disease vaccines needed for - vaccines needed for severe disease, so designed that way. COVID vax in that way work stupendously well
Read 9 tweets

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