If you're fully vaccinated, should you wear a mask indoors?

@WHO, LA Health Dept say yes

CDC says no

Who is right?

Well, it turns out, its nuanced

It depends largely on where you live...and your risk tolerance

My latest op-ed in @BostonGlobe

bostonglobe.com/2021/07/07/opi…
Think of getting vaccinated like getting a great hockey goalie

Like Gerry Cheevers, who blocked 90% of shots on goal

That's like Pfizer: prevents about 90% of infections against Delta variant

So is that good? Yeah

But 90% isn't 100%.

So question is: 90% of what risk??

2/5
If you're in N England, where vaccination rates high, infection rates low

You're unlikely to encounter the virus

But if you do, 90% protection against a small risk is a tiny risk

And you can skip the mask if you want

But if you're in SW Missouri....

3/5
If in SW Missouri, where vax low, infection high

You'll encounter the virus a lot

And 90% protection against a large number is still a sizable risk

So you're much more likely to have a breakthrough infection

Ah you say,

but do you care about breakthrough infections?

4/6
You might care about breakthrough symptomatic infections

They can be miserable
You probably won't get Long COVID but we don't know for sure

You may not care about breakthrough because simply:

You are VERY unlikely to get particularly sick and that's what matters most

5/6
And of course, there is another wrinkle:

Indoor masking can't be enforced on unvaccinated people only without vaccine verification system

So not having mask mandates in high outbreak areas means unvaccinated walking around unmasked. Only drives cases higher

Not great

6/7
So what do I do?

In highly vaxxed N England, I wear mask indoors intermittently

Based on if I'm in a very crowded place or not

If I were in SW Missouri and many other places with low vax, high cases, I'd wear a mask indoor reliably

Your preferences may differ

End

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More from @ashishkjha

8 Jul
As of today,

4 "green" states on @CovidActNow map

3 New England states & South Dakota!

Why green? Because they have very low numbers of infections

How? Largely from population immunity

Lets compare VT and SD -- two states that took different paths to get here

Thread
Vermont and South Dakota are actually very similar

Both have slightly older, white, rural populations

Have comparable median incomes

Both have Republican governors

And these days, they look super similar on infections

Here they are over past 2 months

2/5
But here's where they diverge

Vermont has vaccinated (1+ shot) nearly 75% of its population

SD? 50%

Vermont has a high degree of immunity through vaccinations

So how does SD have high population immunity?

Prior infections

Here's how pandemic has played out in both states
Read 5 tweets
28 Jun
Watching Delta variant take off across world

What will it take to control it?

Vaccines & public health measures of course

Here in US, we're abandoning PH measures (masks, distancing)

So vaccines

How much?

My estimate: 60% of Americans fully vaccinated

We're at 46%

Thread
So why is 60% a reasonable estimate?

Well, lets begin with R0 of Delta

Best credible estimates suggest its around 5

If you had no public health measures, need 80% population immunity to stop spread of the virus

Immunity comes from two sources:

Vaccines
Prior infections

2/n
If 46% have been fully vaccinated,

means 54% not yet fully vaccinated (math!)

But (and this is surprisingly contentious), folks with prior infection obviously have some degree of immunity

Let’s assume they have as much immunity as vaccinated people (I'm not sure they do)

3/n
Read 12 tweets
25 Jun
US has done well on vaccinations

Will it be enough to ward off spike from Delta variant?

Let's look to UK for to peek into our future

A month ago, UK had half the cases (per capita) as the US

Delta was starting to take hold in UK

See graph (US in blue, UK in red)

Thread
Then, over past month, Delta became dominant in UK

So what happened?

See graph

UK's infections increased nearly 6X in the past month or so

And UK cases now 5X that of the US!!

Ah you say -- that's infections. But surely no impact on hospitalizations!

3/6
Actually, hospitalization in the UK are also up

Up nearly 80% from a month ago

With no signs of slowing down

So that's not great

But surely given that UK has vaccinated all of its high risk folks, deaths are falling?

4/7
Read 7 tweets
18 Jun
Important study out of UK

Worth your time

Researchers examined brain MRIs of people before and after they got COVID, matched with controls

What did they find?

Substantial loss of grey matter in those who had gotten but recovered from COVID

Thread

medrxiv.org/content/10.110…
Loss of grey matter (thickness and volume) suggests damage to areas of the brain

Which areas?

Areas involved in smell/taste, cognitive function, and memory formation

And the kicker?

Most of COVID patients examined had had mild to moderate disease in the past

2/3
So what does this mean?

1 Appears to be good evidence that infections lead to neurologic damage in some portion of people

2 severity of neurologic effects not related to severity of initial disease

3 we have to begin to put effort into long-term effects of COVID

And....

3/4
Read 4 tweets
17 Jun
Key feature of the Delta variant is everyone needs both shots of the mRNA vaccines to be protected

But national vaccination data suggests about 10% of people have missed their 2nd shot

That's about 18 million people

And those 18M aren't spread evenly across the US

thread
So some math

As of today, there are 29M people with 1 shot

Based on daily vaccination rates, about 11M of those 29M are in window between 1st and 2nd shot

Leaving about 18M people who missed 2nd shot.
That's 10% of folks who started getting vaccinated

But....
People missing 2nd shot varies widely by state

In Hawaii, nearly 1 in 4 people who got their first shot missed their 2nd shot

Utah is at 20% of people missing their 2nd shot

IL (18%), PA (16%), and Arkansas (15%) round out worst 5

So who's good?

3/5
Read 6 tweets
29 May
Tempting to look at vaccinations in US by states

And it makes sense: states have a lot of control over vaccination sites, outreach, etc

But there's ton of variation within states

So let's talk Massachusetts, a super high vaccination state

Its a tale of two cities

Thread
Lets look at two of the larger cities in Massachusetts

Springfield and Newton

Springfield 3rd largest with a population of 150K

Newton 11th largest with a population of 91K

Difference in vaccination rates between them?

Stunning

So let's go to the numbers

2/5
Springfield:

12% of kids aged 12-15 with at least 1 shot
55% of people over 20
64% of people over 30

Newton:

64% of kids aged 12-15
93% of people over 20
99% of people over 30

That's not a typo. 99% of people over 30!!

3/6
Read 7 tweets

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