By Brianna Abbott and Thomas M. Burton
Public health experts are increasingly calling for a shift in thinking about Covid-19 testing: It is better to get fast, frequent results that are reasonably accurate than more precise results after dayslong delays.
Diagnostic companies are racing to develop quicker, cheaper Covid-19 diagnostic tests, and tests that can be done at doctors' offices, nursing homes and other places with the assistance of a medical provider are gradually becoming more widespread.
The U.S. Food and Drug Administration has authorized four such tests that are antigen-based, meaning they search for viral proteins. Test makers have vowed to produce tens of millions of these quick-turnaround tests in coming months, including Abbott Laboratories which recently unveiled a test that costs $5 and is the size of a credit card.
Several companies also are working on at-home rapid tests that people can perform themselves. No test is currently authorized for complete at-home use, in part due to regulatory requirements for ease-of-use and accuracy.
Covid-19 tests that don't require a lab tend to be less sensitive than "gold standard" laboratory-based tests, meaning they are likely to miss more cases. But many public health experts now say that repeat testing can make up for the loss of sensitivity, and such testing could quickly identify the most infectious people and help bring transmission to heel as workplaces and schools resume in-person operations and as influenza season looms.
"When we looked ahead, we realized we needed a paradigm shift from the still-needed diagnostic tests to the screening tests," said Jonathan Quick, managing director for pandemic response, preparedness and prevention at the Rockefeller Foundation, which released a report in July calling for a massive scale-up in quick, cheap tests for Covid-19 screening. "As a practical matter, that meant making much more of a new kind of test," Dr. Quick said.
Most Covid-19 diagnostic testing in the U.S. is processed in laboratories and uses a technique called rt-PCR that searches for the virus's genetic material and amplifies it. The tests are incredibly sensitive but expensive to run, and the process often requires shipping samples from a test site to a lab.
In July, demand for Covid-19 tests overwhelmed the major U.S. commercial laboratories, which delayed results for days or sometimes weeks, rendering much of the information practically useless.
"I think there's a sense of desperation that we need to do something else," Ashish Jha, dean of Brown University's School of Public Health, said at a media briefing in August.
What is needed, some public-health specialists say, is a shift to cheaper, more routine testing among people who don't show any symptoms to identify those who can potentially spread the virus. That would involve making a distinction between Covid-19 testing for patient diagnosis and testing for public-health screening.
For one-shot diagnostic testing, doctors need tests that are relatively quick but as accurate as possible. But for screening purposes in settings such as workplaces or prisons, a less-sensitive test, such as an antigen test, would be good enough to catch most cases and isolate those with an infection while relieving pressure on labs.
With frequent testing, cases missed the first time around might be caught a few days later. That is more effective for screening than a highly-accurate test done once a month or once a week, which would give the virus more time to spread, public health authorities say.
"If you wait a week, it's too late," said David Walt, co-leader of the Mass General Brigham Center for Covid Innovation in Boston and co-founder of Sherlock Biosciences, a diagnostics company that is working on point-of-care and at-home Covid-19 testing based on Crispr gene-editing technology.
Antigen tests are better at identifying cases when people have more virus in their system -- meaning they will likely find people when they are most infectious, said Michael Mina, an epidemiologist at the Harvard T.H. Chan School of Public Health and an advocate of low-cost, widely available at-home testing that can be done on a paper strip.
Governors from 10 states have partnered with the Rockefeller Foundation to acquire millions of antigen tests. The federal government also has placed large orders for antigen tests to be sent to nursing homes and assisted-living facilities, and for allocation to schools and first responders, Adm. Brett Giroir, Trump administration testing coordinator, said last week.
Pennsylvania Gov. Tom Wolf said a Bethlehem-based diagnostic company, OraSure Technologies Inc., is expanding operations to support manufacturing of its rapid at-home antigen test. The company aims to have it on the market by year-end, OraSure Chief Executive Stephen Tang said.
"We wouldn't have made that decision if we hadn't had so much robust interest," Dr. Tang said, noting he has fielded calls from schools, government agencies and other employers.
The National Institutes of Health last week said it was awarding additional grants in the Rapid Acceleration of Diagnostics (RADx) Initiative, totaling $129.3 million, to companies including two makers of portable Covid-19 testing devices and one that doesn't require any specialized equipment.
A high regulatory bar for authorization is one reason quick, at-home testing for consumers has yet to hit the market, said David McManus, co-director of the Center for Advancing Point of Care Technologies at UMass Medical School, who is involved with the RADx program.
At-home test manufacturers have to show the FDA that the public can grasp the instructions, take the test and interpret results correctly, without assistance. If the manufacturer wants authorization for a test that can screen asymptomatic people, it must meet an additional set of standards. Some companies in point-of-care testing want to also adapt the technology for at-home use as a next step.
The FDA also has said that rapid tests should have comparable accuracy to PCR diagnostic tests -- a requirement that some public health specialists and companies say is overly stringent for surveillance testing.
An FDA official noted sensitivity rates lower than PCR might be acceptable, depending on how the test results are used. The agency has allowed for antigen tests with a sensitivity rate of 80% or better, the official said. "You can even have lower than 80% sensitivity" if it is a recurring or serial test.
Antigen and other non-lab tests might require follow-up testing to confirm results, public health authorities say, as false negatives and even occasional false positives are likely to occur.
Kelly Wroblewski, director of infectious diseases at the Association of Public Health Laboratories, said she had concerns about rapid tests for asymptomatic people because data on their efficacy in these people is lacking. "We always struggle with the perfect being the enemy of the good," she said.
Adm. Giroir last week said there are ongoing academic and commercial studies of the efficacy of tests on people without symptoms. He said the tests could be used for asymptomatic people, even if they weren't authorized for that purpose. "I don't think there's a difference biologically in terms of viral load between symptomatic and asymptomatic, " he said.
Even when more rapid tests do get approval, manufacturers will have to produce enough of them to enable wider, repeated use, and the results need to make it to public health officials, public health authorities say. It isn't clear who would pay for wider screening testing, with many employers and schools currently picking up the tab.
The Centers for Disease Control and Prevention recently softened its Covid-19 testing guidelines, saying that people who have been exposed to a Covid-19 patient but who don't have symptoms don't necessarily need a test. That sparked criticism from public health authorities who say that close contacts and other asymptomatic people should be tested to help control the pandemic.
--Sarah Krouse and Anna Wilde Mathews contributed to this article.
Write to Brianna Abbott at firstname.lastname@example.org and Thomas M. Burton at email@example.com
Corrections & Amplifications
This item was corrected on Sept. 9, 2020 to show that governors from 10 states have partnered with the Rockefeller Foundation to acquire millions of antigen tests. An earlier verison incorrectly said that more than two dozen states, cities and tribes had entered into the partnership.