Thread by @MonicaGandhi9

HOW MUCH CAN VACCINATED PERSON TRANSMIT WITH DELTA? Answer is - we don't know, but most certainly less than unvaccinated person and good to be humble and say "I don't know'. Why did we universally mask early in the pandemic (April 3 CDC guidelines?)
ncbi.nlm.nih.gov/pmc/articles/P…

To prevent asymptomatic transmission. By November 9, 2020, when CDC changed guidelines to "masks protect you and others, it was clear that it is more fit and filtered masks that protect you; cloth masks not as effective as shown by recent Bangladesh RCT
cell.com/med/pdf/S2666-…

So, CDC put out new guidance on Feb 9, 2021 saying more fit & filtered protect you but not really implemented for worker protection like other places. O but then why did CDC say no masks for vaccinated on May 13 - because, with alpha & early on
cdc.gov/mmwr/volumes/7…

lots of reduction of asymptomatic infection with vaccines (multiple studies below). And so CDC was trying to motivate vaccines by taking masks off the vax'd, which - for anyone who works on behavioral motivation- was wise (don't need condoms + treatment as prevention or PrEP)

And many of us supported it although some very vocal public health people thought too soon but the message "get a vaccine get back to normal" is very powerful for a country to develop (though admittedly, US was only one who removed masks differentially)
washingtonpost.com/outlook/2021/0…

Okay then CDC put masks back on July 27 but the question of whether asymptomatic people who are vax'd spread is not only unresolved but seems very rare by good contact tracing studies, but more on that in minute. CDC did this due to P-town but remember breakthroughs symptomatic

After public became more used to idea that vaccines actually there to prevent severe disease after many articles from virologists reassuring public that this is purpose of vaccines (we develop vaccines for severe illnesses; don't have a vax for common cold), we want to remember

that IgG (systemic immunoglobulins) and IgA (which are produced by the COVID vax) both get into the nasal mucosa and were preventing your ability to spread because they work on the virus right then & there to kill. As antibodies wane, may have less protection there for few days

but the antibodies will come RIGHT back from memory B cells (maybe 3-5 days) which is why mild breakthroughs can happen but your immune response will come to rescue you soon. T cells also in nose! See below - that is point virologists were trying to make
atsjournals.org/doi/full/10.11…

How can vax'd person (even symptomatic breakthrough) spread as readily as an unvaccinated person when immune response will kick in to hobble that virus & render it less infectious as soon as possible. T cells in nose, help memory B cells produce new antibodies adapted to variants

Which is why again and again, please do not only think of antibodies when you think of immune system - think of its complexity. You have adaptive immunity set up to fight virus if you see it again so very unlikely to be infectious to others for long
leaps.org/how-long-do-co…

And indeed, we now have studies that show us that- the day after P-town study published (that didn't do serial viral loads or culture), two nice studies came out- one from Singapore that showed if you take time to look at viral loads by CT over time, drop much faster in vax'd

And this study from Netherlands among 161 symptomatic healthcare worker breakthroughs with delta showed that the virus "more sick" (starting to be attacked) so less able to grow out in culture (less infectious)

And this was a very important study from CID that showed us that with alpha symptomatic breakthroughs, even with the CT (cycle threshold) value on PCR being as low as infections from unvaccinated, virus couldn't be cultured out- already being killed
(academic.oup.com/cid/advance-ar…).

And this amazing recent study from U of Illinois that showed us vaccines quickly diminishes time of transmission potential, minimizes symptoms and restricts tissue dissemination of virus with delta symptomatic breakthroughs
medrxiv.org/content/10.110…

which totally makes sense of course & probably explains Lancet study that showed us such low rates of long COVID with a symptomatic breakthrough with delta (vaccines create cellular memory which quickly kicks into place to produce Abs and amplify T cells)
thelancet.com/journals/lanin…

Now what if you feel perfectly well (asymptomatic) and vax'd? Doubt you are transmitting- only careful contact tracing can tell us if you are. This Singapore study (see website) did just that in time of delta- we got source code & couldn't see asymptomatic vax'd transmission

So, you should feel pretty confident if you are vax'd and asymptomatic (like in a restaurant with vaccine passports) & this information (and more which should come from US contact tracing studies) can help determine masking if asymptomatic and vaccinated

And this is why I think our messaging has been scary and confusing for the past month and we need to bring it back to be more simple and talk to those who are unvaccinated and eligible about why getting vaccinated so important

I also think at some point officials should ensure to message that vaccines are more powerful than masks, please don't underestimate vaccines ever! And that everyone's risk tolerance is different after vax- may have to become individual decision (not mandates) about masking later

Sorry didn't explain well - since viral load in nose comes down more quickly (Singapore, Illinois study) and the virus is more sick because it is being attacked by immunity so can't infect cells well (Netherlands, Illinois study), vax'd person can't spread as well as unvax'd

When scientists tell you a highly contagious variant makes virus endemic, no one is being cavalier. Reality steeped in ID history. A virus has not "won" if we have prevention (vax) for severe disease, treatments for mild & follow hospitalizations closely to decide on normal life.

When I told WaPo that delta brings cases down because of higher immunity in population (finding unvax'd; gives hybrid immunity in those with vax who see delta by accident), reality-facing: the reality that we can someday live with an endemic defanged virus is not being cavalier

As summarized above, spread from asymptomatic vaccinated people low (CDC was talking about symptomatic vaccinated people with breakthroughs in their communications the last week of July)

In terms of accepting endemicity, you can see different countries are in various phases of acceptance. US maybe still hoping to make vaccinated impermeable by boosting antibodies but will fade again & good to focus on unvax'd. Denmark/UK/Ireland accept endemicity with high vax

Much easier to accept endemicity of virus when fewer people getting severe disease. So, easier to accept in UK, Denmark, Norway, Ireland, etc. & harder to accept when severe disease still occurring (US) which we can curb by immunity (most safely achieved by getting unvax'd vax'd)

Endemicity will look like this- outbreaks of severe disease among unvax'd adults; some who get symptomatic breakthroughs will get monoclonal antibodies if needed & eventually antivirals; others with mild colds no treatment. Key to getting through is defanging virus with vax

Paper (during alpha) showing virus can't be cultured if you have in your nose after vax. Makes sense microbiologically because immune system attacks it. As antibodies in nose wane, may take few days for memory B cells to make more to kill delta but will
academic.oup.com/cid/advance-ar…

Control achievable but elimination unlikely with highly transmissible delta. Control with high vax allows return to normal life like we achieved for so many other viruses. Suggest US shift to hospitalization, not case, metrics in restrictions

And finally to increase public health trust during this time, 4 things
1) Acknowledge natural immunity (1 dose?)
2) Vax purpose? Prevent severe disease
3) Immunity only way to get through pandemic
2) Acknowledge restrictions hard; give endpoints for when US allowed normal

oh and acknowledge everyone's risk tolerance after vaccination different & respect differences in your friends. Public health's job? To prevent severe disease; we would never have heard of COVID-19 if it didn't cause severe disease (or developed a vax)
nytimes.com/2021/09/07/bri…

Oh and for those concerned that antibodies in nose wane & takes few days for antibodies to be made by memory B cells, there are T cell islands in the nose after vax or infection too which work on killing virus
biorxiv.org/content/10.110…

This IDSA/AMP statement explains why CT value on a PCR is not a good surrogate for viral load
idsociety.org/globalassets/i…

More data to add to this thread - remember how we said one must look at careful contact tracing studies like in Singapore to see if spread occurring from asymptomatic vaccinated people (not CT values on a PCR test?). Here is one in Peel Canada
peelregion.ca/health-profess…

at indoor sporting event for children not yet eligible for vax. With this large outbreak, no further transmission to fully vax'd household members at home, no further transmission from breakthrough cases (even symptomatic), speaks to immune system swooping in to kill that virus

And here is summary by @sailorrooscout of summer camp data showing vaccinations effective at reducing transmission. Want to message vaccines as a return to normalcy and not message 2021 same as 2020