As the world waits for a safe and effective Covid-19 vaccine, government and public-health officials have continued to focus on the importance of personal behaviors such as social distancing, facial coverings, and testing as the best means to contain the spread of the infection and reduce the number of deaths. Much less public attention has been directed toward the strategic value of Covid testing. Discussions about testing have focused, understandably, on more narrow issues such as test availability and wait times for results. What’s missing is a broader discussion of how testing could be the mainstay of a strategy for controlling spread of the disease that could lead to resumption of normal social and commercial life.
Start with a basic description of transmission dynamics. If two individuals come into close contact, there can be no Covid transmission if neither is infected, or if neither is infected with a significant load of transmittable virus. This is, in essence, the strategy being employed to stop the spread of HIV, with relative success.
As with Covid, HIV is a virus for which there is no vaccine. And, as with Covid, the CDC sees testing for HIV as “a critical component of prevention efforts because when people learn they are infected, research shows that they take steps to protect their own health and prevent HIV transmission to others”—such as adjusting their behavior and taking their medications. Studies have shown that individuals infected with HIV will not have sufficient virus to transmit if they take their HIV medications consistently. Thus, the key to slowing the spread of HIV is a cascade of actions: routine widespread testing, linking infected persons with care, and treatment.
An analogous cascade for Covid would consist of regular testing—including testing of asymptomatic persons with no known infectious contacts—and self-isolation by those found to be infected. This strategy, however, is limited by a lack of available on-demand, reliable, and low-cost rapid testing. Imagine if you could self-administer such a test before visiting people outside your immediate household, or if front-line essential workers could test themselves before returning home to their loved ones. Armed with this reliable information, individuals could take appropriate actions if their tests were positive.
At present, testing is marred by several flaws. It’s still challenging for an asymptomatic person with no known infectious contacts to get a test. The reliability of the tests, especially rapid tests, remains problematic. Rapid tests, which measure pieces of the outer surface of the virus and can be conducted cheaply and outside of a laboratory, are only moderately effective in determining whether someone is infected. They occasionally produce false positives, telling people that they are infected when they are not.
In contrast, the non-rapid, molecular, laboratory-dependent tests are more costly, and the results are not readily available. The effect of this delay—which can exceed the dormancy period of the virus—is worsened in places with the highest infection rates and busiest processing laboratories. As such, we do not yet have the kind of tests we need in order to make testing a true control strategy.
The National Institutes of Health and some diagnostic companies are pushing to develop reliable, low-cost rapid tests as soon as possible. It’s conceivable that such tests may be available sooner than the promulgation of a safe and effective vaccine. The time to raise awareness of testing and self-isolation as a control strategy—modeled on the successful control strategy for HIV already employed in cities and communities around the country—is now.
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