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Why Diseases Can Come Back Stronger: Understanding the Divorce Effect

Diseases don’t always behave the way we expect. Sometimes, efforts meant to reduce infections—such as temporary vaccination campaigns, lockdowns, or mosquito control programs—can make a disease come back even stronger once those efforts end. This surprising phenomenon is known as the divorce effect.

The divorce effect occurs when short-term disease-control measures temporarily suppress transmission, but during that time, fewer people get infected and therefore fewer develop natural immunity. As the number of susceptible individuals silently builds up, the population becomes more vulnerable. When the control measures stop—whether due to cost, policy change, or reduced urgency—the disease finds a large pool of unprotected hosts, allowing it to spread rapidly. The resulting outbreak can be bigger than what would have happened without any intervention at all.

This effect is especially common with endemic diseases, the ones that are always present in a region, and when control strategies aren’t sustained long enough to eliminate the disease completely. It highlights an important truth in public health: temporary control without a long-term plan can backfire.

Understanding the divorce effect helps public-health officials design smarter strategies. It encourages them to consider not just how to stop a disease today, but how to prevent a massive rebound tomorrow. With careful planning, disease control can be effective—and avoid the unintended consequence of a stronger comeback.