Nsikan Akpan, PhD Profile picture
Oct 3, 2020 15 tweets 11 min read Read on X
Some say that herd immunity achieved via regular ol' infection can stop the COVID-19 outbreak and return life to normal

History says they're wrong

For @NatGeo, I dive into herd immunity's origin story and why we need an effective vaccine to maintain it nationalgeographic.com/science/2020/1…
Now, those folks will say "But look at NYC!" where the caseload has been low and steady. This sustained recovery must be herd protection, they argue.

But based on the simple math behind herd immunity, this is a fantasy h/t Virginia Pitzer from @YaleSPH nationalgeographic.com/science/2020/1… Image
Likewise, if Sweden has achieved sufficient herd immunity, then their cases wouldn't be increasing right now at basically the same pace as eight months ago. ourworldindata.org/coronavirus-da… Image
Ok, when most people say "herd immunity," they mean the herd immunity threshold (HIT).

It's the percentage of a population that must be immune to stop a disease's spread.

Paul Fine at @LSHTM explained this simple way to think about it, and I went 🤯🤯 nationalgeographic.com/science/2020/1… ImageImage
.@kennelliott built this cool interactive so you can see the herd immunity threshold in action.

Achieve it, and enough people in your community will be shielded so that a germ can't sustain an outbreak.

It can also set our desires for a COVID-19 vaccine nationalgeographic.com/science/2020/1…
Related: @kennelliott is the best!
Now, when you see "weak vaccine" in a headline, you might think "Oh no, Nsikan has gone anti-vax."

I haven't, but the FDA's minimum goal for vaccine approval (50% efficacy) couldn't establish herd immunity—even if everyone took it 😯😲
nationalgeographic.com/science/2020/1…
Don't misunderstand me. A vaccine with 50% efficacy could still spare hundreds of thousands from hospitalizations, chronic health issues, and death, as @bruce_y_lee explains.

But the sweet spot for saying goodbye to masks/social distancing would be 80%. nationalgeographic.com/science/2020/1… Image
Professor @bruce_y_lee's lab (@PHICORteam) also provided the data behind @kennelliott's interactive, which I'm sharing for a third time because it's awesome. nationalgeographic.com/science/2020/1…
Ok, you may have heard of some models claiming the herd immunity threshold could be as low as 40% (or even 10%) through regular ol' infection, due to something called heterogeneity.

But those models are just that, according to their authors.
nationalgeographic.com/science/2020/1… Image
For sure, the herd immunity threshold will vary from city to city. It might be higher in some, lower in others, says Jeff Shaman of @ColumbiaMSPH

But we're seeing some signs from rapid outbreaks that the simple equation for COVID's threshold might be 🎯 nationalgeographic.com/science/2020/1… Image
Banking on natural infection to control the outbreak could lead to months of dismay. If we've learned anything this week, it's that throwing caution to the wind isn't the best move right now.

(For more on that, peep this story by @michaelgreshko)
nationalgeographic.com/science/2020/1…
And I write all of this because you may have missed yesterday (given the news cycle 😅) that the @theNAMedicine has released a huge report on how to equitably allocate a COVID-19 vaccine. 👀👀👀nationalacademies.org/our-work/a-fra…
One of the report's co-chairs is William Foege. He's best known as a former CDC director.

But when he was 30 years old, and serving as an EIS officer in Nigeria, he helped devise a vaccination strategy that eliminated the final strongholds of smallpox. nationalgeographic.com/science/2020/1… Image

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More from @MoNscience

Jun 10, 2023
NYC officials expected a modest smoke plume to sweep through the area Friday night -- and it did. gothamist.com/news/modest-sm…
Thankfully, the rain helped dampen things, but the city still recorded a moderate bump in AQI around 10 pm.
gothamist.com/news/modest-sm… Image
Yesterday's smoke forecast from NOAA predicted another plume could flow through early Sunday morning (video below).

I checked again this morning that forecast is still holding steady.
gothamist.com/news/modest-sm…
Read 5 tweets
Jan 2, 2022
A Lancet preprint looks at omicron's severity in its early epicenter, Gauteng, South Africa

Many are discussing the overall result: This wave experienced much less severe disease than past waves.

But the age breakdowns tell a slightly different story... papers.ssrn.com/sol3/papers.cf…
Cases: In past waves, people younger than 39 (blue) made up ~50% of cases.

With omicron, they accounted for 67% in this study.

We know that young adults fare better than older ones with COVID, which could be lowering overall severity with the latest wave.
Cases: Another way to look at things...

During the delta wave, young adults (20-39) had a case rate (blue) that was half the rate for seniors older than 60 (red).

During omicron, it flipped. The young adult case rate is now 56% higher.
Read 9 tweets
Dec 20, 2021
Welp, that escalated quickly.

Omicron now makes up 92% of sequenced cases in the New York and New Jersey region, based on the latest data from the CDC. That's up from the 13% reported last week.

Nationally, omicron is 73%, up from 12% reported last week.
covid.cdc.gov/covid-data-tra…
Some important context for this rapid rise:

1. I mentioned to @Steronious on @WNYC this weekend that we might eventually learn that omicron arrived here well before its first detection, based on evidence from overseas... wnyc.org/story/gov-hoch…
I am now wondering if this increase is partially due to increased efforts to find omicron cases. The variant is undoubtedly spreading 2-3x faster than delta...but damn, what a jump!

No matter what is ultimately revealed, we need more resources for genomic surveillance.
Read 11 tweets
Dec 19, 2021
NY reported another 21,908 COVID positives on Saturday — breaking a record for the 2nd day in a row.

But these milestones don't mean the state has reached its worst peak. Far from it...and some signs point to improvement.

Me for @WNYC/@Gothamist
gothamist.com/news/ny-breaks…
Indeed, the U.S. COVID outbreak could be transitioning into an endemic — where the coronavirus would continue to thrive in perpetuity, but vaccinated people would be largely spared the worst outcomes.
gothamist.com/news/ny-breaks…
A COVID endemic would mean riding this rollercoaster of infection waves every few months or perhaps just every winter, and it could be brutal for unvaccinated people.

But it would be eased by better access to testing/masks/ventilation... gothamist.com/news/ny-breaks…
Read 4 tweets
Oct 13, 2021
If You’ve Had Covid, Do You Need the Vaccine? ✍️: ⁦@apoorva_nyc

Spoiler: Yep nytimes.com/2021/10/12/hea…
“Some consistent patterns have emerged: Two doses of an mRNA vaccine produce more antibodies, and more reliably, than an infection with the coronavirus does.”

nytimes.com/2021/10/12/hea…
“Only 85 percent to 90 percent of people who test positive for the virus and recover have detectable antibodies to begin with. The strength and durability of the response is variable.”
nytimes.com/2021/10/12/hea…
Read 4 tweets
Sep 3, 2021
Today @NYCMayor de Blasio told @BrianLehrer that @WNYC/@Gothamist's recent series on ventilation in @NYCSchools is inaccurate

He should read our latest:

NYC Officials Say School Windows Can Always Offer Solid Ventilation. Independent Scientists Disagree
gothamist.com/news/nyc-offic…
And as a fun exercise in science media literacy, let's break down the Mayor's response...
Two weeks ago, Brian Lehrer asked @NYCMayor/@BilldeBlasio whether he had heard that the air purifiers @NYCSchools had purchased for every classroom in the city lacked HEPA filters, an industry standard.

The mayor said he'd look into it.
wnyc.org/story/ask-mayo… Image
Read 15 tweets

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