How the Swiss Cheese Model Can Help Us Beat Covid-19

Laveta Brigham

In hopeful news this week, Pfizer and its partner, BioNTech, released interim results from an ongoing trial of their candidate coronavirus vaccine. The study involved 43,538 volunteers who were randomly assigned either the vaccine or a placebo. The rates of infection were small for both groups, but those who got […]

In hopeful news this week, Pfizer and its partner, BioNTech, released interim results from an ongoing trial of their candidate coronavirus vaccine. The study involved 43,538 volunteers who were randomly assigned either the vaccine or a placebo. The rates of infection were small for both groups, but those who got the placebo were substantially more likely to get Covid-19 (85 or more cases) than those who got the treatment (just 9 cases or fewer). This is a terrific development, but it should be noted that even among those who got the vaccine, the infection rate was not zero.

It’s important to understand that a vaccine, on its own, won’t be enough to rapidly extinguish a pandemic as pernicious as Covid-19. The pandemic cannot be stopped through just one intervention, because even vaccines are imperfect. Once introduced into the human population, viruses continue to circulate among us for a long time. Furthermore, it’s likely to be as long as a year before a Covid-19 vaccine is in widespread use, given inevitable difficulties with manufacturing, distribution and public acceptance.

Controlling Covid-19 will take a good deal more than a vaccine. For at least another year, the U.S. will have to rely on a multipronged approach, one that goes beyond simplistic bromides and all-or-nothing responses. Individuals, workplaces and governments will need to consider a diverse and sometimes disruptive range of interventions. It helps to think of these in terms of layers of defense, with each layer providing a barrier that isn’t fully impervious, like slices of Swiss cheese in a stack.

In fact, the “Swiss cheese model” is a classic way to conceptualize dealing with a hazard that involves a mixture of human, technological and natural elements. The British psychologist James Reason introduced the model more than three decades ago to discuss failures in complex systems such as nuclear power, commercial aviation and medical care. As Prof. Reason argued, “In an ideal world each defensive layer would be intact. In reality, however, they are more like slices of Swiss cheese, having many holes…. The presence of holes in any one ‘slice’ does not normally cause a bad outcome. Usually, this can happen only when the holes in many layers…line up…bringing hazards into damaging contact with victims.”

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