Analysis: The science behind the rapid-response COVID-19 tests that could save the Pac-12’s season

The Pac-12’s return to competition depends on one unexpected development solving two momentous problems. The late September arrival of rapid-response antigen tests — two months earlier than anticipated — will allow football teams to test players for COVID-19 immediately before practice and games, thereby preventing on-field transmission by pre-symptomatic or […]

The Pac-12’s return to competition depends on one unexpected development solving two momentous problems.

The late September arrival of rapid-response antigen tests — two months earlier than anticipated — will allow football teams to test players for COVID-19 immediately before practice and games, thereby preventing on-field transmission by pre-symptomatic or asymptomatic players.

Those same antigen tests, courtesy of a partnership with San Diego-based Quidel Corp., are central to clearing the other hurdle:

Convincing health officials in Oregon and California to lift state restrictions and allow the six teams to move forward with practice and competition.

The three NFL teams in California long ago received exemptions from the state, in large part because of their ability to test players on a daily basis.

The Pac-12’s testing plan, however, isn’t identical to the NFL model.

It’s better.

“From a theoretical perspective, it’s a very high bar, and you could argue that what we’re doing is a higher bar (than the NFL),” said Dr. Kim Harmon, a University of Washington football physician and key member of the Pac-12’s medical advisory team.

“The near-daily testing should keep the athletes safe.”

The Pac-12 would be wise to make that very case to authorities in Oregon and California — the sooner the better — in order to avoid getting left behind in what could be a costly race.

The Big 12 and ACC are playing.

The SEC gets underway in two weeks.

The Big Ten is on the brink of restarting its season, possibly in the middle of October.

At that point, the Pac-12 would be the only member of the Power Five on the sideline.

The perception of the conference nationally, already poor, would deteriorate further.

“That’s on top of everyone’s minds,’’ commissioner Larry Scott told KJR radio in Seattle last week. “But health and safety take precedence.”

The rapid-response antigen tests are an escape hatch for the Pac-12— a means of keeping the players safe and salvaging the conference’s reputation.

They’re expected to arrive by the end of the month, for use on a daily basis by athletes in six contact sports: football, men’s and women’s basketball, men’s and women’s water polo, and wrestling.

Harmon believes implementation could take several days, at least. Each school must train staff members to administer the tests, record the results and report the data to local health agencies.

Waivers must be signed.

Testing space must be created.

Protocols must be established.

“It’s not as simple as going to the drug store and buying a pregnancy test,’’ she said.

If the antigen tests are in place by early October, the conference could begin an abbreviated season in early to mid-November — but only if Oregon and California lift their restrictions.

(Scott told KJR that it was “highly unlikely” the conference would proceed without all 12 teams.)

While Oregon Gov. Kate Brown and her staff have hinted they would not let the Beavers and Ducks get left behind the rest of the conference, the political challenge in California isn’t so much about clearing a hurdle as it is climbing El Capitan.

The Pac-12 needs the antigen tests and Alex Honnold.

Example No. 1: The Rams opened their season at home Sunday but seven miles away, USC cannot congregate in groups of more than 12 players.

Example No. 2: The 49ers opened at home on Sunday but 15 minutes up the road, Stanford is prohibited from having more than two players touch the ball on any given play.

The key difference in the level of state restrictions, Hotline sources believe, is the testing:

With their immense resources, NFL teams can conduct daily PCR tests to prevent the spread of the virus. In contrast, the Pac-12 teams have been unable to test players daily.

But that will change when the Quidel antigen tests arrive.

Harmon’s comparison of the Pac-12 testing plan to the NFL’s model required a qualifier — “from a theoretical perspective” — because the rapid-response antigen tests aren’t as sensitive as the PCR tests and haven’t been in use for as long.

But according to data from the medical experts’ presentation to the presidents in August, the antigen tests should be more effective than the PCR tests in driving down the rate of infection.

That information is based on research by a handful of scientists that included Colorado assistant professor of computer science Daniel Larremore and Michael Mina, an epidemiologist and immunologist at the Harvard School of Public Health.

In a preprint of their paper published earlier this summer — it had not been peer reviewed at the time — the authors determined that “testing frequency was found to be the primary driver of population-level epidemic control.”

Frequency, not sensitivity, is the key to containment because of the rate the virus grows once it enters the body.

Scientists believe that infectiousness occurs when there are approximately one million copies of the virus (per milliliter) in the body, Harmon said.

But unless a contagious person coughs in your face for 10 minutes, a typical COVID-19 exposure doesn’t instantly produce one million copies — it could be more like 50,000 or 100,000 copies.

Because of exponential growth, that initial figure could become one million copies within 24 or 48 hours.

Now, overlay that growth rate with the different testing protocols.

The PCR tests used by the NFL have a 24-hour turnaround time because of the need for a reagent to amplify the  DNA and RNA, and for a laboratory machine to process the sample.

Depending on the time the PCR test is administered to an NFL player, his viral load at that moment and the time required for results to become available, a player could unknowingly take the field with an infectious level of virus.

It’s not likely, but it’s possible — hence the 98% reduction in infectiousness assigned to the daily PCR testing regimen by the Larremore and Mina study.

“There’s a little window when it can sneak in,’’ Harmon said.

The antigen tests made by Quidel are not as sensitive as the PCR tests — they don’t detect the virus until higher load levels have been reached.

But they’re more effective in reducing infectiousness because of the 15-minute turnaround time.

“An important variable in surveillance testing is the time between a test’s sample collection and the reporting of a diagnosis,’’ wrote Larremore, Mina and the other scientists in their June 2020 paper.

“… These results highlight that delays in reporting lead to dramatically less effective control of viral spread and emphasize that fast reporting of results is critical in any surveillance testing.”

Here’s how the antigen tests, in theory, would prevent viral spread across the Pac-12 football teams:

Let’s say a player is tested before practice and is positive. That’s easy: He’s held out and isolated.

If the player tests negative, that could mean 1) he’s truly negative (no virus in the body) or 2) he’s infected, but not at a level that would register on the antigen test.

And that’s OK, because if the viral load doesn’t register on the test, it’s not significant enough to be infectious.

Immediately after the negative test, the player could participate in a full-contact practice (or game) without risking transmission because the virus won’t reach the one million copies threshold during the window of close contact.

“In the four hours I’m playing,” Harmon said, “I’m not infectious.”

The next day, that same player would have enough copies to test positive, and the isolation process would begin.

The 15-minute turnaround time, in theory, eliminates the possibility of a contagious player taking the field.

It also greatly reduces, or eliminates altogether, the need for contact tracing.

For that reason the daily antigen tests are believed to reduce infectiousness 100%.

They aren’t designed for personal care, because the sensitivity isn’t high enough.

Instead, they’re considered a public health measure, because they eliminate spread.

The next step for the Pac-12, it seems, is convincing officials in Oregon and California to listen to the science behind the antigen tests.

“There are a lot of layers to get through in all this,” Harmon said of the Pac-12’s attempt to restart the season, “and sometimes, it makes my head explode.

“But this is a really rigorous process.”

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