When the highly transmitted version of the Omicron coronavirus arrived in the United States last fall, it pushed the number of new cases to unprecedented peaks.
Even then, the record wave of registered infections was a significant underestimation of reality.
In New York, for example, employees registered more than 538,000 new cases between January and mid-March, representing approximately 6 percent of the city’s population. But a recent study of adults in New York suggests that there may have been more than 1.3 million additional cases that were either never detected or never reported – and that 27 percent of adults in the city may have been infected during these months.
The official number of coronavirus infections in the United States has always been underestimated. But as Americans increasingly turn to home testing, state-run mass testing sites and institutions are reducing surveillance tests, the number of cases is becoming an increasingly unreliable measure of the virus’s true mortality, scientists say.
“Blind spots appear to worsen over time,” said Dennis Nash, an epidemiologist at CUNY’s University of Public Health and Health Policy, who is leading a preliminary analysis of New York that has not yet been published.
This could leave employees increasingly unaware of the spread of Omicron’s highly contagious new sub-variant, known as BA.2, he said, adding: “We are more likely to be surprised.” On Wednesday, New York officials announced that two new sub-variants of Omicron, both derived from BA.2, have been circulating in the state for weeks and are spreading even faster than the original version of BA.2.
The official number of cases can still mark the main trends and began to increase again with the spread of BA.2. But counting is likely to be a bigger problem in the coming weeks, experts said, and mass testing sites and widespread surveillance tests may never return.
“This is the reality we are in,” said Christian Andersen, a virologist at the Scripps Research Institute in San Diego. “We don’t really look at the pandemic like we used to.
To track BA.2, as well as future options, staff will need to derive what they can from a range of existing indicators, including hospitalization rates and wastewater data. But actually monitoring the virus will require more creative thinking and investment, scientists said.
For now, some scientists have said, people can assess their risk by implementing a lower-tech tool: paying attention to whether people they know become infected with the virus.
“If you hear your friends and colleagues getting sick, it means your risk has increased, and it means you probably need to test and mask,” said Samuel Scarpino, vice president of pathogen surveillance at the Rockefeller Foundation Pandemic. Institute for Prevention.
The problem with testing
Tracking the virus has been a challenge since the earliest days of the pandemic, when testing was severely limited. Even when tests improved, many people did not have the time or resources to look for it – or had asymptomatic infections that never came to light.
By the time Omicron came along, a new challenge had emerged: home tests were finally becoming more widely available, and many Americans relied on them to get through the winter holidays. Many of these results have never been reported.
“We have not laid the groundwork for systematically capturing these cases nationally,” said Caitlin Jetelina, an epidemiologist at the University of Texas Health 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 work may be needed to get people to use them. Residents of six communities across the country were invited to use an app or online platform to order free tests, register their results, and then, if they chose, send that data to their state health departments.
Nearly 180,000 households used the digital assistant to order the tests, but only 8 percent of them registered any results on the platform, the researchers found, and only three-quarters of those reports were sent to health professionals.
Covid’s general fatigue, as well as the protection vaccination provides against severe symptoms, could also lead to fewer people seeking testing, experts said. And citing a lack of funds, the federal government recently announced it would stop reimbursing healthcare providers for testing uninsured patients, prompting some providers to stop offering these tests for free. That could make uninsured Americans particularly willing to test, Dr. Jetelina said.
“The poorest neighborhoods will have even lower cases than high-income neighborhoods,” she said.
Monitoring trends in cases remains important, experts said. “If we see an increase in cases, this is an indicator that something is changing – and it is very likely that something is changing due to a greater shock to the system as a new option,” said Alisa Bilinski, a public health expert at the School of Public Health. of Brown University.
But more modest increases in transmission may not be reflected in the number of cases, meaning it could take more time for employees to discover new leaps, experts said. The problem may be exacerbated by the fact that some jurisdictions have started to update their data less frequently.
Dr. Nash and his colleagues are exploring ways to address some of these challenges. To estimate how many New Yorkers may have been infected during Omicron’s winter jump, they surveyed a diverse sample of 1,030 adults about their behavior and test results, as well as potential exposure and symptoms to Covid-19.
People who report a positive test for the virus in tests performed by health care providers or test providers are counted as cases that would be captured by standard surveillance systems. Those who tested positive only at home tests were reported as hidden cases, as well as those who had probable undeclared infections, a group that included people who had both Covid-19-like symptoms and known exposures. of the virus.
The researchers used the answers to calculate how many infections may have escaped detection, weighing the data to match the demographics of the city’s elderly population.
The study has limitations. It relies 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 jumps, Dr. Nash said.
“You can do these surveys on a daily or weekly basis and quickly adjust real-time prevalence estimates,” he said.
Another approach would be to replicate what Britain has done by regularly testing a random selection of hundreds of thousands of people. “This really is a Cadillac of observation methods,” said Natalie Dean, a biostatistician at Emory University.
However, the method is expensive and Britain has recently begun to reduce its efforts. “This is something that should be part of our arsenal in the future,” said Dr. Dean. “It’s not clear what people have an appetite for.”
Severity of the disease
The proliferation of Omicron, which easily infects even vaccinated people and generally causes milder disease than the earlier version of Delta, has led some employees to put more emphasis on hospitalization rates.
“If our goal is to track down a serious disease from the virus, I think that’s a good way to do it,” said Jason Salemi, an epidemiologist at the University of South Florida.
But hospitalization rates are lagging behind and may not catch the real victims of the virus, which can cause serious disruption and prolonged Covid without sending people to the hospital, Dr Salemi said.
In fact, different indicators can create very different portraits of risk. In February, the Centers for Disease Control and Prevention began using local levels of hospitalization and hospital capacity measures, in addition to the number of cases, to calculate new “Covid-19 community levels” designed to help people. to decide whether to wear masks. or take other precautions. According to the measure, more than 95 percent of U.S. counties currently have low levels of Covid-19 in the community.
But the CDC community transmission card, which is based solely on local cases and levels of positive test results, suggests that only 29 percent of U.S. counties currently have low levels of viral transmission.
Hospitalization data may be reported differently from one place to another. Because Omicron is so transmitted, some localities are trying to differentiate between patients who have been specifically hospitalized for Covid-19 and those who accidentally caught the virus.
“We felt, because of the internal factors of the virus itself that we see circulating in our region now, that we need to update our indicators,” said Dr Jonathan Ballard, chief medical officer at the New Hampshire Department of Health and Human Services.
Until the end of last month, the Covid-19 online dashboard in New Hampshire showed all inpatients with active coronavirus infections. It now shows instead the number of hospitalized patients with Covid-19 receiving 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 said.)
Another solution is to use approaches such as monitoring wastewater that does not rely on testing or access to healthcare at all. People with coronavirus infections excrete the virus in their feces; monitoring the levels of the virus in wastewater provides an indicator of how widespread it is in the community.
“And then you combine that with sequencing to get an idea of what options are circulating,” said Dr. Andersen, who is working with colleagues to track the virus in San Diego’s wastewater.
The CDC recently added wastewater data from hundreds of sampling sites to its Covid-19 dashboard, but coverage is highly uneven, with some states reporting no current data. If wastewater monitoring will fill the gaps in the tests, it must be expanded and data must be released in near real time, scientists said.
“Wastewater is meaningless to me,” said Dr. Andersen. “This gives us a really good, important passive monitoring system that can be scaled. But only if we realize that this is what we need to do. “
Dr Scarpino of the Institute for Pandemic Prevention said there were other sources of data that staff could use, including information on school closures, flight cancellations and geographical mobility.
“One of the things we don’t do well enough is put them together in a thoughtful, coordinated way,” Dr. Scarpino said.