Each week, more than 500 people make their way to Weyerhaeuser Hall on the Macalester College campus in St. Paul, where they swab the insides of their lower nostrils under medical supervision to get tested for COVID-19.

The students and employees, selected semi-randomly by a computer to provide nasal samples for COVID testing, have no symptoms of the disease and no reason to suspect they're infected.

And that's the point.

When COVID-19 case counts fall, doctors and public health officials say the importance of finding and isolating asymptomatic carriers will re-emerge as a top priority for ending the pandemic. An analysis published last month in JAMA Network Open estimated more than half of all COVID-19 transmission originates in people who don't know they are infected.

Even in Minnesota, where residents can get COVID-tested for free, advocates of routine asymptomatic testing say it remains critical that schools and organizations can access cheap and quick ways to regularly test their students or employees.

"The prevalence of asymptomatic individuals is high enough that identifying them reduces the spread," said Macalester Vice Provost Paul Overvoorde, director of campus COVID operations. "Vaccines will certainly play a role, but they are still months from being able to curb the active epidemic."

Testing, along with social distancing, masking and other basic pandemic steps, will remain important for months to come, Minnesota Health Department officials say.

The soonest any vaccine will be available in the U.S. for kids ages 12 to 15 is late spring, and it will be even longer for those who are younger.

Scientists don't yet know if vaccinated people can still spread the virus.

"We have indicators that there will be some continued spread, even among people who are vaccinated, until enough people are vaccinated to shut down the disease," said Harvard professor Dr. Atul Gawande.

Gawande, known widely for writing about reforming health care, is co-founder and executive chairman of CIC Health, in Cambridge, Mass., which connects organizations that need testing — including Macalester — with laboratories that can process large volumes of tests quickly and cheaply.

Macalester's twice-weekly batches of test specimens from asymptomatic students and employees are processed by the University of Minnesota Genomics Center (UMGC), which set up a new lab in Oakdale in October.

The masked and gloved workers at the lab open the tubes on-site and create "pooled" vials containing samples from five individuals. Negative pool results are available that day, and positive pools come back the next morning. The tests are run on QuantStudio 5 PCR machines.

"If it's negative, all individual results are negative. If the pool is positive, we go back to retest those five individual samples immediately," said Kenny Beckman, director of the UMGC.

Latest COVID statistics

Diagnostic testing for COVID-19 has declined in Minnesota along with overall case counts.

The week before Thanksgiving saw the state's highest test volume, with more than 400,000 molecular and antigen test results reported and a positivity rate exceeding 10%. Since the start of the new year, half that many tests have been reported each week, with positivity rates of 5% or less.

Meanwhile, vaccination rates in the state are expected to accelerate in coming weeks, with the U.S. introduction of the one-shot vaccine from Johnson & Johnson and growing supplies of the existing two-shot vaccines made by Moderna and Pfizer/BioNTech.

On Thursday, Gov. Tim Walz announced any adult in the state who hasn't been vaccinated by this summer will be eligible to get a vaccine. The state expects to vaccinate 70% of Minnesotans 65 or older by the end of March.

More than 878,000 Minnesotans have received one dose of the Moderna or Pfizer vaccines, and nearly 453,000 have completed both doses. About 51% of seniors have gotten at least one dose, state data show.

The Minnesota Health Department on Sunday reported eight additional deaths from complications of COVID-19, including four who lived in long-term care or assisted-living facilities. The fatalities included a person in their early 30s, another in their late 50s, and the rest were between 65 and 99.

State officials also reported 813 newly confirmed cases, bringing the state's total to 484,594.

The state has reported 57 cases of the COVID variant first discovered in the U.K., known as the B.1.1.7 variant. Minnesota also had two of the nation's six total cases of a variant first found in Brazil, known as P. 1, according to the CDC.

Testing still key

The Centers for Disease Control and Prevention encourages organizations and employers to consider periodic COVID-19 testing in return-to-workplace planning.

But it's not the top recommendation.

A survey of more than 1,100 businesses in 29 countries by Arizona State University last fall found 17% of employers were testing their employees. Common reasons for not testing were cost and complexity.

Theresa Adams, a senior adviser at the Society for Human Resource Management in Alexandria, Va., said employers in lower-risk industries appear likely to adhere to basic steps such as temperature checks, health questionnaires, masking and social distancing.

While asymptomatic carriers are a legitimate concern, Adams said, "I haven't heard that there will be increased testing because of that. I think employers will most likely continue to use their screening processes and the CDC guidelines."

Organizations such as CIC Health and private labs like New York's Mirimus Clinical Labs are encouraging the use of "pooled" testing to cut the cost and time needed to get diagnostic test results using molecular testing.

A non-peer-reviewed study from Mirimus examined 250,000 of its real-world saliva test results from 111 schools and universities, grouped in pools of up to 24 of their peers, and found pooling lowered costs while allowing consistent detection.

Results were provided in six to 12 hours, and tests ranged from about $13 to $17 per person. The tests can be cheaper for public schools, and private companies may pay $20 to $25 per test, knowing that they're subsidizing schools.

"We have had zero complaints from the companies, because a lot of them are paying $75 to $100 per test. So we are cutting their costs dramatically," Mirimus CEO Dr. Prem Premsrirut said.

UMGC has price points of $13, $19, $22 and $30 per tests that pool five specimens per vial at the lab. Lower prices are for larger and long-term commitments, since that reduces UMGC's costs.

CIC Health handles contracting, software and other services so the labs can focus on molecular biology. Clients like Macalester pay CIC Health $36 to $46 per test. CIC Health pays UMGC $22 per to test Macalester specimens, UMGC's Beckman said.

"What we're trying to do is design systems for low cost," Beckman said. "My view is that once we can get testing to be affordable and very [efficient], you can use it as one of the tools in stopping new outbreaks, because you'll catch them earlier."