When the highly transmissible Omicron variant of the coronavirus arrived in the United States last fall, it pushed the number of new cases to peaks never seen before.
Even then, the record wave of recorded infections was a major count of reality.
In New York City, for example, officials reported more than 538,000 new cases between January and mid-March, representing about 6 percent of the city’s population. But a recent New York adult survey suggests that there could be more than 1.3 million additional cases that were never detected or never reported, and that 27 percent of adults in the city could have been infected during these months.
The official count of coronavirus infections in the United States has always been underestimated. But as Americans increasingly turn to home testing, states close mass testing sites, and institutions reduce surveillance testing, case counts are becoming an increasingly unreliable measure. of the true toll of the virus, scientists say.
“Blind spots seem to get worse over time,” said Denis Nash, an epidemiologist at the CUNY Graduate School of Public Health & Health Policy who led the New York City analysis, which is preliminary and has not yet been completed. has published.
That could leave officials increasingly in the dark about the spread of Omicron’s new highly contagious subvariant known as BA.2, he said, adding, “We’ll be more likely to be surprised.” On Wednesday, New York officials announced that two new Omicron sub-variants, both descended from BA.2, have been circulating in the state for weeks and are expanding even faster than the original version of BA.2.
The official case count may still pick up important trends and has started to rise again as BA.2 spreads. But lower counts are likely to be a bigger problem in the coming weeks, experts said, and massive test sites and widespread surveillance testing may never return.
“This is the reality we are in,” said Kristian Andersen, a virologist at the Scripps Research Institute in San Diego. “We really don’t have our eyes on the pandemic like we used to.”
To track BA.2, as well as future variants, officials will need to extract any information they can from a number of existing indicators, including hospitalization rates and wastewater data. But really keeping track of the virus will require more creative thinking and investment, scientists said.
For now, some scientists said, people can measure their risk by implementing a lower-tech tool: paying attention to whether people they know are catching the virus.
“If you hear your friends and co-workers get sick, it means your risk has increased, and that means you’ll probably have to get tested and masked,” said Samuel Scarpino, vice president of pathogen surveillance for the pandemic. Rockefeller Foundation. Institute of Prevention.
The problem with the tests
Virus monitoring has been a challenge since the early days of the pandemic, when testing was very limited. Even when the tests improved, many people did not have the time or resources to look for them, or had asymptomatic infections that were never reported.
When Omicron arrived, a new challenge presented itself: home testing had finally become more widely available, and many Americans relied on it to spend the winter holidays. Many of these results were never reported.
“We haven’t laid the groundwork to systematically capture these cases nationwide,” said Katelyn Jetelina, an epidemiologist at the University of Texas Health Sciences Center in Houston.
Some jurisdictions and test manufacturers have developed digital tools that allow people to report their test results. But a recent study suggests that they may need work to get people to use them. Residents of six communities across the country were asked to use an online app or platform to request free trials, record their results, and then, if they wished, submit that data to state health departments.
Nearly 180,000 households used the digital assistant to request the tests, but only 8% of them recorded the results on the platform, the researchers found, and only three-quarters of those reports were sent to health officials. .
According to experts, the general fatigue of Covid, as well as the protection offered by vaccination against severe symptoms, can also cause fewer people to get tested. And citing a lack of funding, the federal government recently announced that it would stop reimbursing health care providers for the cost of testing patients without insurance, prompting some providers to stop offering these tests for free. This could make uninsured Americans especially reluctant to try, Dr. Jetelina said.
“The poorest neighborhoods will have an even more depressed number of cases than the high-income neighborhoods,” he noted.
Monitoring case trends remains important, experts said. “If we see an increase in cases, it is an indicator that something is changing, and most likely that something is changing due to a bigger shock to the system, as a new variant,” said Alyssa Bilinski, a policy expert. of public health of the Institute. Brown University School of Public Health.
But more modest increases in transmission may not be reflected in the case count, which means officials could take longer to spot new increases, experts said. The problem could be exacerbated by the fact that some jurisdictions have started updating their case data less frequently.
Dr. Nash and his colleagues have been exploring ways to overcome some of these challenges. To estimate how many New Yorkers may have been infected during the rise of Omicron in the winter, they surveyed a diverse sample of 1,030 adults about their behaviors and test results, as well as possible exposures and symptoms of Covid-19.
People who tested positive for the virus in tests administered by health care providers or tests were counted as cases that would have been detected by standard surveillance systems. Those who tested positive only at home were counted as hidden cases, as were those with probable unreported infections, a group that included people who had both Covid-19-like symptoms and known exposures to the virus.
The researchers used the answers to calculate how many infections could have escaped detection, weighting the data to match the demographics of the city’s adult population.
The study has limitations. It is based on self-reported data and excludes children as well as adults living in institutional settings, including nursing homes. But health departments could use the same approach to try to fill in some of their blind spots, especially during the waves, Dr. Nash said.
“You can do these surveys daily or weekly and quickly correct real-time prevalence estimates,” he said.
Another approach would be to replicate what Britain has done, regularly testing a random selection of hundreds of thousands of residents. “This is really the Cadillac of surveillance methods,” said Natalie Dean, a biostatistician at Emory University.
The method is expensive, however, and Britain has only recently begun to reduce its efforts. “It’s something that should be part of our arsenal in the future,” Dr. Dean. “It’s not clear why people are hungry.”
The spread of Omicron, which easily infects even vaccinated people and usually causes a milder disease than the previous Delta variant, has led some officials to place more emphasis on hospitalization rates.
“If our goal is to keep track of serious virus disease, I think it’s a good way to do it,” said Jason Salemi, an epidemiologist at the University of South Florida.
But hospitalization rates are lagging indicators and may not capture the true toll of the virus, which can cause severe disruptions and a long Covid without sending people to the hospital, Dr. Salemi said.
In fact, different metrics can create very different portraits of risk. In February, the Centers for Disease Control and Prevention began using local hospitalization rates and hospital capacity measures, as well as case counts, to calculate its new “Covid-19 community levels.” “, which are designed to help people decide whether to wear masks. or take other precautions. More than 95 percent of U.S. counties currently have low levels of Covid-19 in the community, according to the measure.
But the CDC community transmission map, which is based solely on local cases and test positivity rates, suggests that only 29 percent of U.S. counties currently have low levels of viral transmission.
Hospitalization data may be reported differently from place to place. Because Omicron is so transmissible, some localities are trying to distinguish between patients who were specifically hospitalized. per Covid-19 and those who caught the virus by chance.
“We feel like, because of the intrinsic factors of the virus itself that we are seeing circulating in our region now, that we had to update our metrics,” said Dr. Jonathan Ballard, medical director of the New Hampshire Department. Health and Human Services.
Until the end of last month, the New Hampshire Covid-19 online dashboard showed all hospitalized patients with active coronavirus infections. Now, however, it shows the number of patients hospitalized with Covid-19 taking remdesivir or dexamethasone, two first-line treatments. (Data on all confirmed infections in hospitalized patients remain available through the New Hampshire Hospital Association, Dr. Ballard noted.)
Another solution is to use approaches, such as wastewater monitoring, that do not depend at all on testing or access to health care. People with coronavirus infections shed the virus in their feces; monitoring virus levels in wastewater provides an indicator of the distribution of the virus in a community.
“And then you combine it with sequencing, so you have an idea of what variants are circulating,” said Dr. Andersen, who works with colleagues to monitor the virus in San Diego’s wastewater.
The CDC has recently added wastewater data from hundreds of sampling sites to its Covid-19 control panel, but coverage is very uneven, with some states reporting no current data. If wastewater monitoring is to fill the gaps in the tests, it must be expanded and the data must be published in near real time, scientists said.
“Sewage is a no-brainer for me,” Dr. Andersen said. “It gives us a very good and important passive surveillance system that can be scaled up. But only if we realize that’s what we need to do.”
Dr. Scarpino of the Pandemic Prevention Institute said there were other sources of data that officials could take advantage of, including information on school closures, flight cancellations and geographic mobility.
“One of the things we’re not doing well enough is bringing them together in a thoughtful, coordinated way,” Dr. Shoe.