Infectious Disease Experts Answer the Who, How, and When of COVID Testing

Damian McNamara

October 26, 2021

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Infectious disease experts today highlighted the pros and cons of expanding home COVID-19 testing during a media briefing sponsored by the Infectious Diseases Society of America.

They also answered questions about rapid testing for school, work, or travel; when testing of vaccinated individuals might make the most sense; and addressed some controversies that continue to swirl around COVID-19 testing.

Dr Nira Pollock

"We all remember the beginning of the pandemic when there was very little access to testing. We have evolved tremendously since then, and even with so many more options, it's actually still challenging," said Nira Pollock, MD, PhD, associate medical director of the Infectious Diseases Diagnostic Laboratory at Boston Children's Hospital and an infectious disease specialist at Beth Israel Deaconess Medical Center.

Even with the advances, COVID-19 test costs and access remain an issue for some, supplies can be limited, and even though pharmacy chains like Walgreens and CVS offer testing, some people report difficulty getting an appointment, said Pollock, who is also associate professor of pathology and medicine at Harvard Medical School.

Home Is Where the COVID Test Is

Or, at least home is where it may be soon. Home testing capabilities are set to expand, driven in part by the US Food and Drug Administration's authorization of an additional home-based assay this month and by the $1 billion in federal funding pledged by the Biden administration to ramp up home test kit production. The White House also just pledged an additional $70 million to boost access to the rapid, over-the-counter tests.

Of the two main types of at-home tests, molecular tests like polymerase chain reaction (PCR) assays have the advantage of greater sensitivity. However, results require a sample be mailed to a lab — so the downside is the longer wait time.

The majority of home tests are rapid antigen assays. Antigen COVID-19 tests sacrifice some sensitivity for greater convenience for individuals concerned about symptoms or infection status in general.

In terms of performance, "we know that antigen tests have lower analytical sensitivity than PCR, so they're less sensitive at picking up the virus," Pollock said. "They have advantages of rapid turnaround time and lower cost."

A controversial area is whether antigen test results can be used to gauge the infectiousness of an individual, she added. "This is a something that is getting a lot of discussion."

Despite some limitations, Pollock said, "the tests have a role and a negative antigen test is still useful."

Reading and Reporting Results

The expansion of home testing could come at a cost of tracking the number of Americans testing positive or negative at any given time. In other words, commercial labs and organizations are obligated by law to report their data. Consumers, not so much.

Dr Dial Hewlett Jr

"We will probably lose track of…what the prevalence of the disease actually is at any given at any given time," Dial Hewlett Jr, MD, medical director of the Division of Disease Control at the Westchester County Department of Health in White Plains, New York, and an IDSA fellow, said during the briefing.

"On the other hand, I think that having access to these results in a very rapid way will be helpful in terms of the practical issues," he said, including requirements for school, work, or travel.

Ideally, some of the new federal funding could go to education, training, or oversight of at-home testing to increase the likelihood that results are interpreted accurately, Pollock said. "We know that sensitivity and specificity can be impacted by the home environment."

"Even if someone has all of the best intention, they need to know how to how to do the test and interpret the result." One proposal, for example, would provide experts to observe home testing via teleconferencing, but that could substantially add to the cost, Pollock added.

Testing to Support In-Person Learning

As if school administrators haven't had enough grapple with in the past 18 months, "schools are wondering what to do about home testing results," Pollock said.

Research has demonstrated relatively low transmission of SARS-CoV-2 in schools when safety protocols are adopted, including mask wearing, proper ventilation, and distancing.

"But now that everyone is back at school — which is critical for development — we've had to relax distancing measures and so there are more close contacts," Pollock said.

A "test to stay" program is one potential strategy for schools trying to balance in-person learning and personal safety. Essentially, students who may have been exposed to COVID-19 in school can still attend classes in person rather than quarantine at home if they are asymptomatic and test negative for SARS-CoV-2.

The goal of such a tactic, Pollock said, "is to keep students learning in school rather than quarantining them at home." This approach involves daily diagnostic testing of the child's in-school and close contacts as defined by the program with rapid antigen tests for up to 7 days.

"It's a very interesting program," she said. "It's still a ton of work for school nurses, for contact tracing, and for testing overall. It seems to be going well and is having an impact in keeping kids in school."

The Centers for Disease Control and Prevention is considering recommending 'test-to-stay' programs in schools to replace quarantining, Reuters has reported.

Testing the Vaccinated

Despite some initial hope that fully vaccinated individuals could forego COVID-19 testing, the emergence of breakthrough infections changed that scenario.

Practically speaking, Hewlett said, a lot depends on the situation. For example, consider a situation in which family members are planning to gather for the holidays. All are vaccinated. However, one person attending the festivities is being treated for advanced cancer.

"That might be a situation in which testing of everyone would be indicated," he said.

On the other hand, COVID-19 testing may "not be as necessary," Hewlett said, if everyone getting together is healthy, which would be a lower risk scenario.

When a fully vaccinated person is symptomatic, Pollock said, "the answer is very clear. The symptomatic person who's vaccinated should still get tested."

Less clear is the value of widespread testing of asymptomatic, vaccinated individuals, Pollock said. That is a "bigger question," she added, because "vaccination doesn't prevent infection. There's no question of its import but you can still get infected and can still transmit if you are vaccinated."

Primed for Future Pandemics

A potential silver lining of the COVID-19 pandemic is that it fueled advances in testing and the number of options, expanded sample collection to include saliva, and set up public health officials to respond faster and more precisely if and when the next pandemic strikes.

"We should all be thinking about [what is next] as this pandemic evolves," Pollock said.

Future advances are likely to come from past experience, she said. The beginning of the pandemic was a very stressful time for trying to develop tests for the virus. Hospitals, manufacturers, and laboratories all scrambled initially to overcome barriers to rapid, accurate testing.

"I think that everyone has learned a lot from that experience," Pollock said.

When a novel pathogen next emerges, tests could be developed more rapidly and decisions about the optimal testing strategy could come sooner, for example.

No matter what, it's important to be prepared, Hewlett said.

An analogy to a local fire department can be "very useful for people that are not in the medical field," Hewlett said. "You may see the people in the fire department playing cards and sort of sitting around, enjoying the warm weather." He said people might ask themselves, 'Do we really need all of these people to do this?'

Then, 2 or 3 days later there's a high-rise fire and the firefighters are there, risking their lives, trying to save people's lives and put the fire out.

"Pandemics are very much like serious fires," he said. "We have to prepare for them," emphasizing that now is the time for allocating more research and resources to pandemic prevention.

"So that when the fire does come, we actually have a plan in place for it," Hewlett said.

Damian McNamara is a staff journalist based in Miami. He covers a wide range of medical specialties, including infectious diseases, gastroenterology, and critical care. Follow Damian on Twitter:  @MedReporter.

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