Today, because there is a high degree of population immunity, the ability of the virus to cause severe disease and death is far more variable. Someone vaccinated a month ago is not as vulnerable to severe disease as someone who recovered from an infection 18 months ago. If there are 1,000 infections in Massachusetts today, the number of those that will develop into severe illness depends on whether the individuals are vaccinated, boosted, previously infected or immunologically naïve (that is, neither previously infected nor vaccinated). The mix of those four categories varies dramatically across the nation. That’s why relying entirely on cases to dictate risk no longer makes sense, and shifting to measures of severe disease levels, like hospitalizations, is much more appropriate.

In some places, there are plenty of hospital beds and staff and therefore, hospitalizations don’t cause the same stress as they would in places with far less capacity. Think of a city like Boston with many large hospitals versus rural Ohio where there are far fewer resources per capita. In that context, a surge of hospitalizations in Boston has fewer dire consequences than one in rural Ohio. Hospital capacity matters enormously, not just to care for patients with Covid-19 but to secure all the essential services that hospitals provide under normal circumstances. One of the tragedies of Covid surges is that when hospitals get stretched, they can no longer provide high-quality care for patients with heart attacks, injuries from car accidents, appendicitis, cancer or the myriad other conditions that need to be treated. That’s why paying close attention to health care capacity is a welcome change in a nation with large variations in that capacity.