Thread by @methodsmanmd

Thread:
Even a mediocre vaccine can end the pandemic. But there are some caveats. I wrote about this on vox.com last week,
vox.com/21528373/vacci…
but here are the highlights: (1/n)

Let's assume that, on average, every person with COVID-19 can infect 2 additional people (a bit lower than the R0 of 2.5 but makes math easier). (2/n)

To stop the pandemic, we need to prevent disease in 1 out of every 2 people.
So if the vaccine is 100% effective, we'd need to vaccinate 50% of the population.
(Technically vaccinate or infect 50% of the population but trying to stay simple.)
(3/n)

With a less effective vaccine, some proportion of people we vaccinate aren't protected. So we have to vaccinate MORE people to end the pandemic.
(4/n)

This is bad, because we know from studies like this that the less effective a vaccine is, the less people are willing to take it.
(5/n)
jamanetwork.com/journals/jaman…

What if the vaccine is only 50% effective? Well, a bit of math would tell you that (assuming one person infects two others on average), we need to vaccinate 100% of the population to end the pandemic. That ain't happening.
(6/n)

But that assumes that one person infects two others. Actually, in practice, it's much less than that (thanks to masks, social distancing, etc). The better we are at those things, the less people we have to vaccinate to end the pandemic. rt.live
(7/n)

Here's the number of people we'd have to vaccinate to end the pandemic assuming a 50% effective vaccine, under various Rt values. As you can see, if we can keep the Rt below 1.4 or so, we can end the pandemic with a pretty bad vaccine if just 50% of people get it.
(8/n)

The catch is that for that strategy to work we have to KEEP distancing, KEEP masking, KEEP avoiding indoor gatherings (yup, that means Thanksgiving) until we squash new infections.
(9/n)

In this light, vaccines are a bit like masks. You should get one because it's good for society. It's a piece (along with masks, etc) of what we all need to do to get though this.
(10/n).

And we absolutely CAN get through this. A bit of hard work, a bit of sacrifice now, and by this time next year we'll be preparing for the best Thanksgiving we've ever had.
(11/n).

Health professionals: we need to get ahead of this. We need to promote vaccination even if vaccine efficacy is not amazing. Even a mediocre vaccine can work if we work with it. (12/12).

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