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The 3 pandemic metrics that could tell us what’s next

Covid-19 case numbers aren’t as reliable these days. How can we keep track of the virus?

A hotel employee rolls a luggage cart beside a car. A sign beside them reads “Welcome back. Thank you for practicing physical distancing. Stay 6 feet apart.”
This new phase in the pandemic demands a fresh approach to the Covid-19 data that has become omnipresent in the last two years.
Spencer Platt/Getty Images

As the United States transitions out of a pandemic footing and into a new normal, it is also undergoing a shift in which Covid-19 metrics most accurately tell the story of the pandemic. The old standbys — case numbers, namely — aren’t as reliable anymore. So what’s going to replace them?

At least three data sets are now being watched closely by the public health experts who spoke to Vox. Together, they help shed light on what’s happening now, what’s likely to happen, and how well we’re doing at dealing with what’s already happened over the course of the pandemic.

The first, hospital data, covers the present, showing the level of severe illness in a given area and the strain being put on the local health care system. The second, new data on emerging variants, concerns the future and the potential for radical mutations to send the pandemic spinning out into a dangerous new direction. And the third, data on long Covid, reaches from the past and further into the future, as scientists attempt to gain a better grasp of the collateral damage the virus has left in its wake after infecting roughly 60 percent of the US population in the past two years.

Keep in mind that the most important pandemic metrics have been a moving target since 2020. The percentage of tests that came back positive was watched closely as an indication of how widespread the virus was in a given place at a given time. But nowadays, with so many people taking at-home antigen tests and never reporting the results to anyone, most experts consider that metric now to be unreliable. Case numbers, the raw count of positive tests, were an obvious signal to watch for a long time too; not only did they track the crests and dips of different waves, any growth in cases was predictably followed by a rise in hospitalizations and deaths in the subsequent weeks.

But many experts have stopped tracking cases too closely as well. They have the same reporting problem — if you get a positive at-home test result but don’t report it, your case doesn’t show up in the official count — but it’s more than that. Covid-19 is going to be around in the future, as society and the economy are adjusting to a new reality in which most people are expected to tolerate a certain risk of contracting Covid-19. If the public health goal is no longer to constrain case numbers, then they aren’t as meaningful in telling us whether or not our public health strategy is achieving its goals.

Instead, what many public health experts are tracking now is severe illness, meaning hospitalizations and deaths. The data coming out of local hospitals can still give us a good idea of the toll Covid-19 is exacting, the strain it’s putting on local health systems, and early indications that existing immunity may be fading.

“I’m not watching case rates. We expect there to be lots of mild cases,” Bill Schaffner, the medical director of the National Foundation for Infectious Diseases and a professor at Vanderbilt University, told me. “But if hospitalization rates start to go up, there’s probably more substantial waning immunity from vaccines and previous infections.”

This is a new phase in the pandemic. There’s broader testing, vaccines, treatments, and new variants. Public health interventions are ending, leaving individuals to make their own risk assessments and choices about how to protect themselves. All of that demands a new approach to the coronavirus data that has become omnipresent in the last two years.

The most important metrics for the current phase of the pandemic

The dozen public health experts I contacted for this story were unanimous: They will watch hospital data most closely going forward. Some of those experts are still keeping tabs on cases as a general sign of the trends on the ground and because of the potential effect of long Covid to have a lasting effect in even mild cases.

But others said they were discarding cases as a major indicator, given the reporting limitations and the reality that society is shifting into a new phase of the pandemic where contracting Covid-19 is treated, for many people, as a tolerable risk. They’re relying instead on metrics that measure the amount of severe disease in a community.

“The vaccines cannot prevent every infection but are excellent in terms of preventing severe disease, and so I am looking at that metric as our metric of success in managing Covid-19 in this country,” Monica Gandhi, an infectious diseases doctor at the University of California San Francisco, told me.

What hospital data can tell us about the state of the pandemic

The overall number of hospitalizations is a good indicator of how prevalent Covid-19 is in a given community at a given time. But some number of Covid-19 hospitalizations may end up proving incidental, like if a person came to the hospital for a different reason and merely tested positive for the coronavirus as part of routine screening.

That’s why some experts said they were also looking specifically at the number of ICU patients admitted with Covid-19, more likely to be a real indicator of a severe Covid case, and the number of deaths attributed to the virus. Increases in those numbers would be a sign of something worrisome, either the virus evolving to become more lethal or existing immunity starting to wane.

ICU beds filling up would also mean the hospital runs the risk of not being able to care for all of its patients, which could worsen outcomes for patients and even contribute to unnecessary deaths. As Amesh Adalja, a senior scholar at Johns Hopkins University, told me, “seeing hospital operations compromised because of an influx of Covid-19 admissions” is one of the things that would cause him serious concern.

A rising mortality rate could also be a sign that the virus is evolving to become more dangerous. When I asked David Celentano, who leads the epidemiology department at the Johns Hopkins Bloomberg School of Public Health, what in the metrics would freak him out, he said: “A major increase in mortality, which might be associated with a new variant. That is my nightmare.”

For now, hospitalizations (down 8 percent over the last two weeks), ICU occupancies (down 21 percent), and deaths (down 25 percent) are still declining from their omicron peak. That is part of the reason that, in spite of a recent uptick in case numbers, the US government and businesses are continuing to push toward resuming normal activities. They’re not trying to restrain case numbers anymore; these measures of severe illness have become paramount instead.

The important metrics to watch when new variants are identified

Data on new variants were top of mind for all of the public health experts I consulted. Radical mutations in the coronavirus are one development that could disrupt society’s attempt to get back to normal. New variants are identified through genomic sequencing, though clues about emerging iterations of the virus can also be found in sewage, which is becoming a more integral part of our Covid-19 surveillance network.

Whenever any new variant is identified, experts told me that they are interested in three specific data points: how easily can it be transmitted, whether it causes more severe illness, and how easily it evades immunity from vaccines and previous infections.

“If we had a virus that were to some degree substantially transmissible and could notably evade the protection of our vaccines, then we’d be in trouble,” Schaffner said.

We need a lot more data on long Covid

The other set of data that will determine Covid-19’s long-term consequences is on long Covid. Such long-term symptoms after an infection have loomed large over the pandemic, inspiring fears that a mild case of Covid-19 could still end up affecting patients for months after they ostensibly recover.

But there is still a lot we don’t know about long Covid. Some preliminary surveys have suggested as many as 30 percent of people who get infected with Covid-19 may end up having persistent symptoms. But experts are doubtful the number is actually that high and are pushing for standardized attempts to quantify the problem. In the coming months and years, we should start to get an empirical understanding of how many people are affected, who they are, and what the consequences have been.

“We need a much better study of long Covid. It is real and will likely lead to a sustained cost in terms of chronic illness for a large number of people, but how large that number is remains uncertain,” William Hanage, a Harvard University epidemiologist, told me. “Claims that 30 percent of people who recover have long Covid are not credible. However, even 1 percent would mean a lot.”

The US government, businesses, and society at large are making the pivot to living with Covid-19. The virus is going to be with us going forward, so from hospitals to sewers to long Covid, it’s through these three metrics that the next revelations about where things are heading will be found.