ANALYSIS: The Swiss Cheese Model of Pandemic Defense

Lately, in the ongoing 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, SARS-CoV-2, the virus that causes Covid-19. 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.

“Pretty soon you’ve created an impenetrable barrier, and you really can quench the transmission of the virus,” said Dr. Julie Gerberding, executive vice president and chief patient officer at Merck, who recently referenced the Swiss cheese model when speaking at a virtual gala fund-raiser for MoMath, the National Museum of Mathematics in Manhattan.

“But it requires all of those things, not just one of those things,” she added. “I think that’s what our population is having trouble getting their head around. We want to believe that there is going to come this magic day when suddenly 300 million doses of vaccine will be available and we can go back to work and things will return to normal. That is absolutely not going to happen fast.”

Rather, Dr. Gerberding said in a follow-up email, expect to see “a gradual improvement in protection, first among the highest need groups, and then more gradually among the rest of us.” Until vaccines are widely available and taken, she said, “we will need to continue masks and other common-sense measures to protect ourselves and others.”

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.” ...