Welcome to Public Health On Call, a podcast from the Johns Hopkins Bloomberg School of Public Health,

where we bring evidence, experience, and perspective to make sense of today's leading health challenges.

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This is Stephanie Desmond. Today we turn our attention to the origin story of the COVID-19 pandemic with Tom

Inglesby, director of the Johns Hopkins Center for Health Security. Three years on, we are still

actively debating whether the pandemic was caused when the virus spilled over naturally from

animals in a market, or whether it was somehow caused by a Chinese lab leak. We discuss what we

know, why it matters, and what lessons we can learn for the future.

Let's listen.

Tom Inglesby, thanks so much for joining me.

That's great to be with you.

So we are three years into the COVID-19 pandemic, and we are still debating how it started.

And I'm wondering if you could just remind our listeners sort of the two main theories, I guess here, natural spillover and this lab leak theory.

And I'm wondering if you could talk us through a little bit about the merits of each.

Sure. So yeah, those are the two main concerns or possibilities that are

being considered by governments around the world by scientists. And the first one is that this

pandemic emerged from nature, spilled over from some animal.

And I think the basis for that concern is that about 75% of emerging infectious diseases are found to have spilled over from some animal.

A virus circulating in the animal population came into

humans and then started causing havoc. And so obviously a very serious concern. And we know from

SARS, COVID-1, and that large outbreak that civet cats was determined to be the source animals for the spillover.

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