The Swiss cheese model of pandemic defense

Lately, in the conversation about how to defeat the coronavirus, experts have made reference to the "Swiss cheese model" of pandemic defense.

The metaphor is easy enough to grasp: Multiple layers of protection, imagined as cheese slices, block the spread of the new coronavirus. No one layer is perfect; each has holes, and when the holes align, the risk of infection increases. But several layers combined — social distancing, plus masks, plus hand-washing, plus testing and tracing, plus ventilation, plus government messaging — significantly reduce the overall risk. Vaccination will add one more protective layer. "But it requires all of those things, not just one of those things,"said Dr. Julie Gerberding, executive vice president and chief patient officer at Merck.

In October, Bill Hanage, an epidemiologist at the Harvard T.H. Chan School of Public Health, retweeted an infographic rendering of the Swiss cheese model, noting that it included "things that are personal *and* collective responsibility — note the 'misinformation mouse' busy eating new holes for the virus to pass through."

The concept originated with James Reason, a cognitive psychologist, in his 1990 book, "Human Error." A succession of disasters — the Challenger shuttle explosion, Bhopal, Chernobyl — motivated the concept, which became known as the "Swiss cheese model of accidents," with the holes in the cheese representing errors that accumulate and lead to adverse events.

"This multilayered approach to reducing risk is used in many industries," said Ian Mackay. The following is an edited version of a conversation with the virologist.

Q: What does the cheese model show?

A: The real power of this infographic — and Reason's approach to account for human fallibility — is that it's not really about any single layer of protection or the order of them but about the additive success of using multiple layers.

Q: Where does the "misinformation mouse" fit in?

A: The misinformation mouse can erode any of those layers. People who are uncertain may be swayed by a loud voice proclaiming that a particular layer is ineffective. Usually, that voice is not an expert on the subject. When you look to the experts — usually to your local public health authorities or the World Health Organization — you'll find reliable information.

Q: How can we make the model stick?

A: We each use these approaches in everyday life. But for the pandemic, this all feels new and like a lot of extra work. In the end, though, we're just forming new habits, like navigating our latest phone's operating system. … It might take some time to get across it all, but it's worthwhile. In working together to reduce the risk of infection, we can save lives and improve health. And as a bonus, the multilayered approach can even decrease the number of times we get the flu or a bad chest cold. Also, sometimes slices sit under a mandate; it's important we also abide by those rules and do what the experts think we should. They're looking out for our health.