On multiple occasions, I have characterized testing as the original sin of the COVID-19 pandemic as I believe it to be one of the most critical missteps made in the U.S. response. Without the ability to know who was infected and who was not, undetected chains of transmission spread throughout the country and bubbled up in hot spots where hospitals got inundated. However, in May of 2021 with over one-third of the population fully vaccinated and eligibility expanded to all those above age 12, testing has a different role.
Testing of asymptomatic persons: A very diminished role
Earlier in the pandemic, before widespread vaccine availability, when capacity restrictions and stay-at-home orders were very common, serial rapid testing of asymptomatic individuals to know who was infected with a contagious amount of virus, and therefore a threat to others, was a key unmet need. However, much of the pandemic passed without access to cheap, rapid tests that people could self-administer on a frequent basis as they brushed their teeth each morning. I think the benefit of these tests would have been incalculable in terms of reducing exposures and transmission events but also in allowing people to resume some of their activities largely free from the worry of infecting others.
With cases falling, percent positivity of tests plummeting and the virus largely decoupled from its ability to cause serious disease, hospitalization and death, the value of these tests is also changing. Testing of asymptomatic unvaccinated individuals will increasingly have diminishing returns as the likelihood of truly positive tests, as opposed to false positives, will become rarer. A positive rapid antigen test would need confirmation with a more sophisticated molecular test, or another distinct antigen test all the while a person is in limbo, with their life possibly paused or disrupted, awaiting results. This is particularly relevant to schools but holds true for the general public and also applies to pooled testing. There are very few reasons to test asymptomatic individuals beyond facilitating the COVID-exposed unvaccinated ending quarantine early or the unvaccinated international traveler. Fully vaccinated persons, as the CDC guidance states, should not be tested unless symptomatic.
Symptomatic testing still key
In contrast to the testing of the asymptomatic unvaccinated there remains, and will remain, a need for clinical testing of those with symptoms. Such testing will still occur years from now as COVID-19 will still be circulating and though unable to cause a hospital to go into crisis, it will remain standard practice to diagnose. The diagnostic test for the virus is already part of routine respiratory pathogen panels that test patients for multiple infections simultaneously. Additionally, testing is important to identify new variants of the virus (most of which will be inconsequential) that may have altered attributes. Symptomatic testing will also identify clusters of infections and guide public health investigations of activities contributing to spread in unvaccinated individuals.
Fomenting a testing revolution
The deficient testing response for COVID-19 underscores the need to seriously augment the infectious disease diagnostic capacity throughout the system — in health care facilities, urgent care clinics, doctors’ offices and the home. It should no longer be acceptable to label people as having an undefined viral infection when lurking among those cases could be consequential viral infections that could inform pandemic planning and improve patient care through facilitating better antiviral prescribing and diminish inappropriate antibiotic prescribing for viral infections for which they have no role.
Additionally, the home tests for COVID-19 that were authorized are an opportunity that should not be lost. Indeed, before the pandemic I began a project focused on understanding the barriers to increased home testing for a variety of infectious diseases. Home COVID-19 tests, which should still be employed by symptomatic persons, should be converted to full FDA licensure and be expanded to cover other infectious diseases such as influenza, RSV, strep throat, mononucleosis and sexually transmitted infections (there already is an over-the-counter home HIV test).
COVID-19 testing is here to stay but will take on a very different role as the virus is increasingly denied the ability to cause serious disease or threaten hospital capacity. Symptomatic testing will be a critical capacity to maintain and expand to other pathogens, but the value of asymptomatic testing has lost much of its value and will become riddled with problematic false positive results as prevalence of infection has fallen and the rate of vaccination increases.
Amesh Adalja, M.D., is an infectious disease physician and a senior scholar at the Johns Hopkins Center for Health Security. Follow him on Twitter: @AmeshAA.