CORONAVIRUS

Serology testing, a tool in Iowa's coronavirus strategy, has caveats

Experts so far are uncertain how effective antibodies will be

Iowa's state epidemiologist, Dr. Caitlin Pedati, takes questions April 21 on COVID-19 response at the state emergency op
Iowa’s state epidemiologist, Dr. Caitlin Pedati, takes questions April 21 on COVID-19 response at the state emergency operations center in Johnston. (Zach Boyden-Holmes/Des Moines Register)

DES MOINES — One of the tools employed in the Iowa public health department’s response to the COVID-19 pandemic is serology testing.

Gov. Kim Reynolds makes frequent reference to serology testing during her daily briefings, saying it is one of the tools that helps inform how her administration addresses the pandemic — especially when and where it is safe to relax mitigation steps.

Over the past few weeks, Reynolds determined the expansive public health information at her disposal shows it was safe for her to start the process of reopening Iowa businesses, which she did to varying degrees — first in the 77 counties where the virus has not been as widespread, and then to a lesser extent in the remaining 22 counties that include the state’s largest population centers.

Serology testing looks for the presence of antibodies, which are proteins produced by the body’s immune system to fight disease-causing bacteria or viruses.

Serology tests are being used in the COVID-19 pandemic to help give public health and medical officials a better understanding of how and to what extent the new coronavirus that causes COVID-19 has been spreading, and to what degree the body’s antibodies will protect people from the virus in the future.

Such testing could be especially helpful, experts said, in fighting a disease that has been proven to be present in people who display no or only mild symptoms.

“A test like a serologic test, which looks for the presence of antibodies, is one potential way to understand people who might have been exposed but perhaps didn’t realize it, or weren’t tested,” said Dr. Caitlin Pedati, the state epidemiologist. “A tool like serology might help us understand a little bit more about the patterns and activity level of this virus.”

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However, experts agree it remains undetermined even with serology testing whether humans are producing antibodies that help prevent a repeat contraction of the virus — and if those antibodies are being produced, how long they will be effective?

More research is needed to make those determinations, experts said.

“Decent tests will allow public health to understand what proportion of a sample of a population, or of subpopulations, have already been infected with (the coronavirus), and what proportions remain completely susceptible,” said Dr. Louis Katz, an infectious disease specialist and chief medical officer of the Mississippi Valley Regional Blood Center. “They will be especially useful when population surveys are repeated over time to demonstrate how the infection spreads in the population and for telling us — in many months — when herd immunity has been established, around two-thirds of the relevant population infected for this virus, by infections or vaccination.”

“They are not yet useful at all for advising individual patients about their risk from exposure to the virus,” Katz added. “That is, you cannot use them to say, ‘You are safe.’”

Good news arrived this past week in a new study from China that found new coronavirus antibodies in all 285 test subjects who had been hospitalized with severe COVID-19. Even in that study, more research is required to determine how protective the antibodies are and for how long, experts cautioned.

For now, serology tests are less equipped to predict the future and more equipped to help inform it, experts say.

The federal Centers for Disease Control and Prevention reported its serology testing strategy will help determine how many people have been infected by the coronavirus and how it is spreading through the country.

In California, a recent round of serology testing informed a study that found 4 percent of the state’s residents have antibodies in their blood, an indicator that they have been infected.

If public health officials can gain a better understanding of how widespread the virus is, they can make more informed decisions about when it is safe to relax strategies put in place to slow the disease’s spread, experts said.

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“Knowing how many people have been infected with COVID-19, especially those that were never symptomatic if tested, is important as we plan for getting back to normal life and the potential for COVID impact in the future,” said Tyler Brock, deputy director and laboratory services director for the Siouxland public health department. “The more people that are immune, the less a problem the virus should be. So hopefully this testing can provide some of the answers to the ‘who’s immune’ questions, even though it’s undetermined how long immunity might last.”

Reynolds said that in Iowa, the state has directed serology testing to where outbreaks had occurred at meat processing plants and long-term care facilities.

The state does not publish data on serology test results separately from other types of coronavirus testing.

Black Hawk County officials reported serology testing helped them determine that more than 1,000 workers have been infected by the virus because of an outbreak at a food processing plant in Waterloo. The state had reported just 444 positive tests related to the breakout.

“It’s something that we’ve offered as a way to help again understand a little bit more about the trends of this virus here in Iowa, and it’s something that we’re going to continue to work with our (public health) partners throughout the state on to understand how we can direct resources and make decisions that make the most sense for Iowans for how we live, work and interact,” Pedati said.

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Our most important Coronavirus coverage is free to the public.

If you believe local news is essential, especially during this crisis, please donate. Your contribution will support news resources to cover the impact of the pandemic on our local communities.

All donations are tax-deductible.