How Will We Know that BA.2 is Surging in the US?


  • Increased at-home testing means many coronavirus cases aren’t included in case counts, but health officials have other tools for monitoring COVID-19.
  • Cases are rising in at least 14 states and Washington D.C., driven by the Omicron BA.2 subvariant.
  • That new sub-variant makes up the majority of COVID-19 cases in the U.S.

Coronavirus cases have dropped dramatically in the United States since their peak in January. As the Omicron wave has subsided, mask policies and other mitigation measures have fallen by the wayside, and states have scaled back their COVID-19 data reporting.

But the coronavirus has not disappeared entirely.

Cases are rebounding in 14 states and the District of Columbia, driven partly by the spread of the BA.2 Omicron sublineage.

This variant accounts for over half of sequenced cases in the United States estimates the Centers for Disease Control and Prevention (CDC). It is also reportedly helping to drive a surge in cases in Europe.

Experts are not certain whether the United States will see a similar BA.2 surge. If one does occur, it’s unclear how severe it will be.

Some experts are concerned that new reductions in COVID-19 testing will impair the ability of health officials to see a surge until we’re in the midst of it.

These cutbacks will be exacerbated by the federal government running out of funds to sustain the country’s testing capacity.

In addition, more people have turned to COVID-19 at-home rapid tests, which are largely unreported. One expert estimates that in January and February, rapid tests outnumbered RT-PCR tests by four to six times, reports the Associated Press.

This will leave public health officials with only a partial picture of the community spread of the coronavirus. But experts say that by tracking multiple metrics, they will still be able to see and respond to a rise in cases.

Although the testing landscape has shifted over the past few months, health officials can still make use of the testing that is occurring.

“We may not be able to easily compare what’s been happening over the last few months to what happened over a year ago,” said Brian Labus, PhD, MPH, an assistant professor in the School of Public Health at the University of Nevada Las Vegas.

“But we can compare what we saw [with testing] in the Omicron surge to whatever else is coming down the road because those time periods should both have a large proportion of the population using at-home tests.”

In addition, he said in some areas, rapid tests done through a doctor’s office are reported to public health departments, so these show up in community case counts.

Dr. Anne Monroe, an associate professor at the Milken Institute School of Public Health at George Washington University, said going forward, testing will be used alongside other measures to track surges, whether caused by BA.2 or another variant.

“Case counts will still factor into decision making, in conjunction with other metrics — [such as] new COVID-19 hospital admissions and percent of staffed inpatient beds occupied by COVID-19 patients,” she said.

This shift in tracking the coronavirus is also happening at the federal level.

The CDC recently changed how it assesses community risk to focus more on COVID-19 hospitalization and hospital capacity, although case counts are still included in this calculation.

Using this new method, most of the United States now falls into a low community risk level.

Many experts, though, point out that hospitalizations and deaths are lagging indicators — by the time these metrics increase noticeably, cases have already spiked. This can leave health officials playing catch-up.

“If we had a massive wave hit us today, that wouldn’t show up in hospitalization data for a couple of weeks,” said Labus. “That delay is a big problem.”

In addition, he said different variants can cause different hospitalization rates. So a certain size surge in cases may lead to vastly different numbers of people in the hospital.

For example, the risk of adults being admitted to the hospital with Omicron was approximately one-third of that for the Delta variant, according to a technical briefing from the U.K. Health Security Agency (UKHSA).

Vaccination rates can also impact hospitalizations and deaths in a community.

Data from the CDC showed that during the Omicron surge, unvaccinated people were 21 times more likely to die from COVID-19 compared to those who were boosted and 7 times more likely to be hospitalized.

As a result, communities with low vaccination rates may see a more rapid increase in hospitalizations during a surge, which will impact their hospital capacity, with ripple effects throughout the healthcare system.

Monroe said another metric that can help detect surges — a little earlier than hospitalizations — is emergency department visits for COVID-19.

Even absenteeism data from schools and workplaces can alert public health officials to a potential surge, said Labus. These can also be caused by other respiratory illnesses such as seasonal flu, but they add one more warning light to monitor.

Health officials are also increasingly using wastewater surveillance to look for signs that a potential rise in cases may be about to happen. This can provide an earlier glimpse into a surge.

While many people think of COVID-19 as a respiratory illness, the virus also infects other parts of the body.

Since it affects so many other systems in the body, it shows up in the feces of people who have an infection.

Aaron Packman, PhD, a professor of civil and environmental engineering in Northwestern University’s McCormick School of Engineering, said wastewater surveillance offers several advantages.

“It’s efficient because nearly every sizable municipality has a wastewater collection system that brings all the wastewater to a treatment plant,” he said, “which means there’s a convenient place to take samples and it covers the whole community.”

It’s also a passive system, so surveillance doesn’t depend on people seeking a COVID-19 test or medical care.

Wastewater surveillance can also be used to monitor for new coronavirus variants and detect them when they arrive in a community.

“This is especially useful because not all clinical samples are sequenced, and none of the at-home samples are sequenced,” said Packman.

Wastewater sampling can even monitor other diseases in the community, such as seasonal flu and respiratory syncytial virus, or RSV.

There are limitations to this method. For example, chemicals or other substances in the wastewater can affect the ability of the test to detect the coronavirus.

In addition, “there’s a fair amount of variability in the measurements,” said Packman. “That can make it hard to directly relate the wastewater data to COVID cases.”

However, he said wastewater surveillance works well for highlighting trends that may indicate a surge is about to happen.

Not every community, though, is doing — or can do — wastewater surveillance.

On the CDC’s wastewater surveillance dashboard, the sites are concentrated in a few areas of the country.

Packman said many more locations are being sampled and monitored than appear on the CDC dashboard. This data may be used only at the local and state level.

Still, rural areas may be less likely to have wastewater monitoring, especially if most of the residential homes are on septic systems. Packman said larger septic systems in rural areas — such as for factories or municipal buildings — can be monitored, though.

Each of these tools has its limitations, which can vary depending upon the type of testing being done, the variant that is dominant, the information systems for capturing and sharing the data, and other factors.

However, “taken together, these metrics can be used to determine the COVID-19 community level spread, which can help guide public health decision making,” said Monroe.

This includes increasing the use of other tools that can minimize the impact of the coronavirus on a community.

“Promoting vaccine uptake in concordance with current recommendations and linking people to available COVID-19 treatments are extremely important to preventing severe disease, hospitalization and death,” said Monroe.

Even at-home tests can play a role in reducing the spread of the coronavirus and encouraging people to seek treatment early.

“The results [from these tests] don’t enter case counts, and sequencing is not performed on the samples, which could lead to delays in detection of variants,” said Monroe.

But “home testing is common and may be helpful if individuals who test positive at home subsequently isolate,” she added.

All of this data can also be used by individuals to help them determine their own risk or the risk faced by the most vulnerable community members, such as those with weakened immune systems.