This article represents my own views, not those of the Santa Clara Department of Public Health, where I am a volunteer case investigator and contact tracer.
The virus is winning. Classrooms are empty (or, at best, filled a few days a week), businesses are shuttered, and many people are socially-isolated during holidays that normally celebrate togetherness. And, of course, the death toll of COVID-19 has caused immense suffering and despair. Currently, we are experiencing an unprecedented surge of cases and hospitalizations across the country. For the immediate future, there is little reason to be optimistic — as one public health expert stated, “the next three months are going to be just horrible.”
Recent vaccine developments, however, show glimmers of daylight. On Dec. 11, the first COVID-19 vaccine in the U.S. was approved by the FDA with a limited number of vaccines to be released in December. While most people know that it may be months before they can receive the vaccine, there are other factors which may preclude vaccine-mediated herd immunity next year. Public health officials have warned about public fears over the vaccine, with one study finding that only half of Americans would get the vaccine once it’s available (Experts state that 70% is the proportion necessary for herd immunity). Moreover, others worry that the vaccine could be less effective than reported in the clinical trials or that the virus would mutate, reducing or eliminating the effectiveness of the vaccine. Finally, it may be possible for even vaccinated people to be contagious. For these reasons, one should be realistic about the timeline for vaccine-mediated herd immunity and realize that life might not return to “normal” until the middle of next year or later. (This is not a condemnation of the vaccine; when it is available to you, please take it!)
Besides, we can do better than just to wait for vaccine-mediated herd immunity next year — there are too many children not learning to read, too many Americans at food bank lines, and too many grandparents alone at nursing homes. In the interim, we can change the tides of the war by identifying contagious people through antigen testing and preventing them from spreading the virus.
Dr. Michael Mina, assistant professor of epidemiology at Harvard, has advocated for a mass program of rapid antigen testing. In this system, people would test themselves at home with an antigen test, a type of COVID-19 test which is much faster and cheaper than a molecular test. Because antigen tests are less accurate, if the first test came back positive, they would test themselves again with a more sensitive antigen test. If this confirmatory test came back positive, they would begin their isolation period. Dr. Mina and colleagues have shown that if half of the population tested themselves every four days, it would be possible to slow the spread of COVID-19, similarly to the effects of a vaccine.
What are these antigen tests, and why are they faster and cheaper? The standard COVID-19 test (“molecular test”) amplifies ribonucleic acid (RNA) present in the patient’s upper respiratory tract, often using reverse-transcription polymerase chain reaction (thus, they are also referred to as PCR tests). The RNA produced is compared to known genes of the SARS-CoV-2 genome. This process occurs in a laboratory, a common bottleneck in the testing cycle.
On the other hand, antigen tests do not require a laboratory to give a result. An antigen is any substance that produces an immune response, typically antibodies. In this type of test, when antibodies on a paper strip bind to proteins of the COVID-19 virus, a dark band appears. This same technology is used for at-home pregnancy tests, where the binding of an antibody to a hormone produced by a pregnant person causes the famous two dark lines.
The two different technologies lead to the two different price points: molecular tests have a median price of $129, compared to $5 for an FDA-approved antigen test by Abbott Technologies. While antigen tests are much cheaper than the standard COVID-19 test, this mass testing program would still require billions of federal dollars for manufacturing and distribution. Yet, the ratio of economic benefits to cost of such a program is estimated to be between 4 and 15.
Costs have not been the only barrier to such a program. Because antigen tests have a lower sensitivity (returning positive in the presence of disease) and specificity (returning negative in the absence of disease) than the standard PCR test, they have not been embraced by public health officials nor the FDA. Currently, there are seven antigen tests which have an Emergency Use Authorization by the FDA, but they are only available to laboratories or health-care providers.
However, the sensitivity and specificity of antigen tests should not be compared to molecular tests; antigen tests should be compared to having no test at all. Most people are not able to get tested before engaging in higher-risk activities, like going to work or seeing family. When people are able to get a testing appointment, they may have to wait for hours in long car lines. In my hometown of Newport, Ore., a physician order is required to get a COVID-19 molecular (PCR) test.
Because of the lowered sensitivity and specificity of antigen tests, the FDA has stated that a molecular test is necessary for making COVID-19 treatment decisions. This is precisely correct; antigen testing should be used to prevent the spread of infections, not for the delivery of medical care. If a person tests positive with an antigen test, then they should be given a PCR test to guide clinical decisions. In the meantime, a positive antigen test will signal that the patient should isolate for 10 days, per CDC guidelines. In the CDC antigen-test algorithm, the diagnosis of COVID-19 is also contingent on other factors, including symptoms and exposure type to COVID-19.
Despite the lower sensitivity of antigen tests, the CDC has acknowledged the usefulness of antigen testing for infection control in high-risk congregate settings: “Especially in settings where a rapid test turnaround time is required, there is value in providing immediate results with antigen tests.” Further, lower sensitivity and specificity for antigen tests is not a fait accompli: An antigen test from Abbott Technologies, the same one available for $5, has a sensitivity of 97.1% and specificity of 98.5%, which is comparable to PCR tests.
Expanding our current system of molecular testing has been a long-standing goal, with many experts calling for between 20 and 30 million tests per day, compared to our current capacity of between 1.5 and 2 million tests per day. However, persistent shortages of supplies and backlogs of samples have demonstrated the difficulty of scaling this type of test. Additionally, molecular tests can take between 24-48 hours for results, which is exacerbated by delays in getting testing appointments. As a contact tracer, I’ve seen cases where a positive test result was not returned to the patient until after the 10-day period in which they would have been required to isolate.
Moreover, there is a difference between “COVID-19 contagious” and “COVID-19 positive.” A PCR test can be positive even when the patient is not infectious (i.e., transmit to another person), which happens when viral RNA is present but below a certain, albeit unknown, threshold. This period of being detectable with a PCR test but non-contagious may be months long in some cases. A positive antigen test, in contrast, generally means that someone is infectious and likely to transmit the virus.
However, a mass antigen testing program is not a panacea; a reliance on antigen testing has been blamed for the COVID-19 outbreak at the White House. “Testing isn’t,” as one medical director put it, “a get out of jail free card.” An antigen testing program will still require other public health measures such as mask wearing, social distancing and vaccines. Thus, it is essential that the public is educated on the limits of antigen testing.
Our testing system is not working. We are testing people only after they have transmitted the virus to their coworkers, friends and family. The medical establishment is beholden to paradigms of the past — similarly to the early days of the AIDS epidemic. Antigen tests should be distributed to Americans, allowing them to test themselves when they would not have normally been able to. In the words of Martin Burke, a chemist at the University of Illinois at Urbana-Champaign working on COVID-19 testing, “[T]esting should become a part of life: In the morning you take your cereals, your vitamins, and you quickly check your [COVID-19] status.” We are in a public health crisis and need to start fighting like it. It’s time to change the playbook and start winning.
If you are interested in learning more about rapid antigen testing, visit rapidtests.org. If you would like to contact your representative about rapid antigen testing, text “RAPID TESTS” to 50409.
Contact Ruben Krueger at ruben1 ‘at’ stanford.edu.
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