How effective a COVID-19 vaccine do we need?

In medicine, as in life, nothing is perfect.

This is true of vaccines. No vaccine is 100% effective. Yet, vaccines have produced massive declines in many serious illnesses, and succeeded in eradicating two such illnesses (smallpox in humans and rinderpest in cattle).

Herd immunity

Since COVID-19 has come along, everyone is talking about herd immunity. This is a straightforward idea. Let’s say I’ve never had smallpox. I’ve never been vaccinated against it. But, if you put me in a group of people who are immune to smallpox, I’ll never catch smallpox. Why? Because they can’t catch it to spread it to me.

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Bayes’ Theorem for people who don’t remember much high school math

Yesterday, I posted a link to a great discussion about COVID-19 testing, and the various types of tests that do or will exist, and their strengths/weaknesses.

It can strike many people as strange that doctors’ tests aren’t 100% accurate. (It even surprises some doctors!) No test is perfect.

But, not only are tests not perfect, but even a test that sounds like its very accurate can be misleading if used under the wrong conditions.

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