By Brian Skinner, Esq.
Earlier this week, global airlines called for pre-departure Covid-19 testing for all international passengers to replace the quarantines that they blame for exacerbating the decline in air travel. International Air Transport Association (IATA) Director General Alexandre de Juniac said during an online media briefing, rapid and affordable antigen tests that can be administered by non-medical staff are expected to become available in “coming weeks” and should be rolled out under globally agreed standards.
Airlines are pressing governments to embrace alternatives to blanket travel restrictions hampering their recovery, especially in light of resurgent case numbers in Europe.
Unlike molecular PCR (polymerase chain reaction) tests or antibody tests, antigen tests are diagnostic tools that look for proteins made by Covid-19. Within 15 minutes and for as little as $10, they can detect if someone is infected. But antigen tests are not nearly as sensitive to the coronavirus as the PCR tests currently used for most Covid-19 testing. In fact, by PCR standards, some at-home antigen tests might catch only half or a third of people who test positive on a PCR test.
The reason for the difference is that the tests are looking for different things in different ways. A PCR test, designed to diagnose an individual with infection, can catch very low levels of viral material before or after a person spreads the virus. An antigen test relies on high levels of the virus to be able to detect it. High levels of the virus occur when a person is most likely to transmit the virus to others.
Proponents of antigen testing say that PCR tests, while useful in determining whether an individual is infected with Covid-19, are actually a poor tool in finding people who are most likely to spread the virus. That’s because PCR tests are so sensitive that they are excellent at picking up traces of the virus even after someone has recovered and is no longer infectious. However, one of the reasons the virus is so difficult to stop is because it has the ability to spread from person-to-person before the carrier begins to experience symptoms. In fact, people tend to carry the most live virus the day or so before they begin feeling sick, and the amount tends to quickly trail off in the several days after symptom onset.
So reactive tests like PCR tests are used for people who either have symptoms, a close contact with the virus, or other reason to think they are likely to have caught it. Antigen tests are proactive tests, designed to find cases before they spread the virus more widely making them well matched for finding people with Covid-19 at precisely their most infectious points rather than potentially long after symptoms have arrived and infectiousness has faded, as is more likely now with the long delays in PCR results and contact tracing. Currently, PCR testing is relatively expensive (about $100) and often experiences processing delays that hamstring efforts to stop transmission.
According to an analysis in a June preprint report that hasn’t yet been peer reviewed, just before someone’s infectiousness substantially increases is precisely the crucial time period where the antigen test is most sensitive: detecting viral load at around 10,000 copies. PCR tests, on the other hand, can pick up about 1,000 copies of the virus, which gives them about a day’s head start at finding the virus. But, because of a delay of more than a day in returning results, any benefit is lost. As a result, antigen tests could be “superspreading detectors” — locating those who may be unknowingly infecting others before they know they have the virus.
Several small companies have been developing these simple tests, and the conglomerate 3M is working with MIT on another one. (The new BinaxNOW test from Abbott, authorized August 26, is different — it requires a health professional to administer it, and the patient must have symptoms to get a prescription.)
Could the less reliable antigen testing be used to make it easier for West Virginia to get people tested more regularly (or even test themselves at home)? And could more frequent and rapid results help schools, sports teams and their fans, and businesses open more safely? Are inexpensive, fast, and easily deployable antigen tests the key to unlocking the state’s pandemic-stricken economy?
A recent example of the use of antigen tests suggests it might. Over the Labor Day weekend at the Utopia music festival in the Poconos, approximately 200 people were screened before entering the festival. Pennsylvania caps open-air gatherings at 250 people. All attendees were screened with an antigen Covid-19 test a few days before the event and again at the door. Six were turned away, but organizers say the event was successful at creating a “bubble.” Events like these may serve as a potential model for mass gatherings or other congregant settings.
Fast and affordable antigen testing can be central to a testing strategy that prioritizes infectiousness instead of infections thereby providing an important opportunity to safely reopening schools and the economy.
Dr. Leana S. Wen suggested such a strategy in a recent op-ed where she outlined a framework of risk stratification routinely used in medical decision-making. Those deemed to be low-risk are subject to a quick screening test and if it’s negative, the evaluation stops. Those with a positive test continue with more extensive testing. In cases where the risk is high, such as someone who is symptomatic or has had a recent contact with an infected person, a fast test isn’t enough. Instead, you need the accurate one. Dr. Wen proposes that such a tiered strategy could help identify far more infections than we do now.
If enough lost-cost antigen testing was available, it might be possible to test school children and teachers every morning. Perhaps restaurants and other retail establishments could require a negative test result as a condition of entry. And the ability to take a home test may make the decision to attend an extended family get-together or visit a grandparent in the hospital, much less dangerous.
Of course, experts agree that the use of antigen testing alone will not be enough to defeat the virus. For any strategy to be effective against the virus, masks and social distancing are essential. But because so many presymptomatic and asymptomatic cases are not being detected with the current testing strategy, it makes sense that antigen testing be a component of a strategy to identify people before they are able to spread the infection further without knowing it.
Brian is the former counsel to the West Virginia House of Delegates Judiciary Committee and counsel to the West Virginia Senate Minority Caucus. He was also general counsel to the West Virginia State Health Officer and Commissioner for the Bureau for Public Health. He has almost two-decades of experience as a strategic advisor and chief legal counsel to both executive and legislative branch public officials.