RALEIGH, N.C. (WNCN) — Public health leaders say the “stealth omicron” COVID-19 variant now shows up in most of the samples across North Carolina that they’ve checked.

One question: Are they checking enough of them?

The most recent week showed a total of only 22 samples. The BA.2 variant turned up in 55 percent — but that only adds up to a dozen of them.

“I wouldn’t be able to tell you whether it’s 60 percent of all samples or 40 percent,” said Dr. Dirk Dittmer, whose lab at the University of North Carolina sequences samples from positive COVID tests to determine variants.

“But I’m able to tell you in four weeks that (it will be) 100 percent,” he added. “This is sort of statistics at its best. Yes, the more samples, the smaller the error bars. But once it’s 100 percent, it doesn’t matter how few samples.”

Those sample sizes are a big deal because those variant counts are one of the seven metrics that made the cut for the North Carolina Department of Health and Human Services to continue tracking as it shifted from daily to weekly updates.

“The important part is, we want to predict what happens in September, right?” said Dittmer, one of the leaders of the state's CORVASEQ surveillance program.

“We need to know what variants are," he said. "These are so we can make sure that the vaccines still work. … All of that is to create a knowledge base to predict what happens in the winter and to predict what kind of vaccine we might want to use.”

To get that picture, labs across the state take some samples that are positive for COVID and break them down genetically to determine which variant is involved.

And for the first time, the BA.2 — “stealth omicron” — variant showed up in most of those, appearing in 55 percent of the samples checked during the week that ended March 26.

Here’s the issue: NCDHHS said the total number of samples checked was just 22, with BA.2 making up 12 compared to 10 for the original omicron.

The total number of samples being sequenced has dropped steadily in recent weeks and months. 

During the week that ended Jan. 1, there were more than 1,700, and even as recently as mid-February — at the height of the omicron surge — the total surpassed 1,600.

But for the week ending March 19, there were fewer than 125.

That small sample size might at least partly explain why BA.2 shows up at a much higher rate across the country and the globe than it has so far in North Carolina.

(Source: CDC)

The Centers for Disease Control and Prevention says BA.2 makes up nearly three-quarters of the COVID cases that have been sequenced in the U.S. The World Health Organization sets that rate higher than 85 percent.

Dittmer says his sequencing lab at UNC is much less busy than it once was.

“We’re getting a tenth or 1 percent of what we were getting at the peak,” he said.

He says fewer samples are a result of having fewer positive cases and also reflect the prevalence of at-home testing.

“The rapid home tests don't enter the system anywhere, right?” he said. “That means the people are infected, they take care of themselves, but they don't show up.”

Dittmer says the slowdown has given his lab the chance to review the past two years and take stock of what has worked and what hasn’t.

“I think CORVASEQ is now at a stage where we can look back and think about lessons learned, and tweak the system so it is in a perfect chain shape when the next wave comes,” he said. “All of these adjustments — in a car, you would do an oil change. All of these are possible now because we're not in the acute emergency system and all of these will be in place for the next wave.”

CBS 17’s Joedy McCreary has been tracking COVID-19 figures since March 2020, compiling data from federal, state, and local sources to deliver a clear snapshot of what the coronavirus situation looks like now and what it could look like in the future.