Thread by @MoNscience

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…

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…

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…

.@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…

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…

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…

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…

@angie_rasmussen @AbraarKaran @SaskiaPopescu @EricTopol @scifri @FemiOke