Writing for the New York Times, Ashish Jha, dean of the Brown University School of Public Health, explains how Covid-19 in the United States has changed throughout the pandemic, as well as the metrics that should be used to develop public health guidance going forward.

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A new phase of the pandemic

According to Jha, national Covid-19 guidance throughout the past two years has largely been based on the number of new cases—a decision that made sense when it was first implemented since "a reliable proportion of those cases would result in hospitalizations, and a proportion of those hospitalizations would lead to death," Jha writes.

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This "tight link" between cases and severe disease was the "bedrock of guidance" for public health measures, such as mask wearing, social distancing, and widespread testing. However, the United States is now at a very different place with the pandemic that it was nearly two years ago.

Currently, there is a high degree of population immunity in the United States, both from vaccination and natural infection—but immunity varies dramatically across the country. This means that the coronavirus's ability to cause severe disease and death is "far more variable," Jha writes.

In addition, "the [o]micron surge changed everything," as it has a "high degree of immune evasiveness," which allowed it to infect even people who have been vaccinated or previously infected. And compared to the delta variant, omicron appears be less virulent, although it can still be deadly for those who are unvaccinated.

Overall, omicron "caused a very large surge in cases and left in its wake a very different reality" than what the United States experienced previously during the pandemic, Jha writes.

The Covid-19 metrics the U.S. should focus on now

In recent weeks, several U.S. states have lifted Covid-19 restrictions amid falling case and hospitalizations numbers. In addition, CDC on Friday updated its masking guidance with new metrics and loosened mask recommendations for most of the U.S. population.

According to Jha, CDC's new metrics for assessing Covid-19 "mark a turning point for how people, institutions, and governments should respond" to the pandemic. Instead of relying solely on case numbers, CDC now considers multiple metrics, including hospitalizations and hospital capacity, to assess Covid-19 risk in a particular area.

Jha also notes that hospital capacity is important to consider since cities with many large hospitals will be able to deal with a surge of hospitalizations much more easily than rural areas, which often have fewer resources per capita.

"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," Jha writes. "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."

However, Jha writes that increases in Covid-19 cases are still "an important early warning signal" for severe disease, so including them in "the portfolio of metrics guiding policy," like what CDC is doing now, is still important.

Overall, Jha shares that CDC "must be willing to update its guidance when facts change and to take into account where Americans are in their ability to adhere to recommendations." The new metrics that pay attention to hospital capacity will help account for large variations in immunity and resources as the pandemic continues.

"As Americans enter this new phase of the pandemic, mitigation efforts like masking, testing and avoiding gatherings will remain important tools to manage the spread of the disease, especially when there's threat of another surge," Jha writes. "Changing the way we use these tools—when to pull them out and when to put them away—is a critical part of managing a pandemic effectively. The [CDC]'s new guidance does just that by focusing on the metrics that matter most at this point in the pandemic." (Jha, New York Times, 2/25)