Early in the pandemic, the United States had an undertesting problem. Now we are overtesting those who are immune and asymptomatic. A person with immunity to the coronavirus will fight off an infection. But during and after the person’s exposure to the virus, it’s common for a low number of virus particles to be detectable in the nose. In medicine, we call this virus a “colonizer” — a pathogen that does not cause illness or spread the illness. It’s an incidental finding. But in today’s world of routine coronavirus testing of vaccinated people, these positive tests are inflating the number of positive cases in a misleading way.
It is true that the delta variant has led to an increase in cases in parts of the country where vaccination rates are low, and these surges need to be taken seriously; these cases correlate with increases in serious illnesses and hospitalizations mainly among the unvaccinated. What we’re concerned about is the overtesting of the fully vaccinated, who now make up roughly 60 percent of U.S. adults. The Centers for Disease Control and Prevention has officially decreed that fully vaccinated people should not be tested for the coronavirus in the absence of symptoms. That’s because immunity works. Mounting evidence has demonstrated an extremely low risk of asymptomatic transmission by vaccinated people.
But despite this guideline, testing vaccinated people with no symptoms is a bandwagon that cannot seem to be stopped. Employers, entertainment venues, schools, airlines, local governments and even hospitals are adopting universal testing policies regardless of vaccination status. This results in asymptomatic immune people testing positive even though they pose no substantive public health threat. This practice was evident even at the White House’s outdoor Fourth of July party, where each of the more than 1,000 attendees was tested for the coronavirus. We can assume that many of Biden’s staff and friends who attended were vaccinated. So unless they had symptoms (which would preclude them from attending, anyway) this testing was not consistent with CDC guidelines.
Testing people who have been vaccinated and have no symptoms could extend this pandemic forever. That’s because a PCR test, which still remains the gold standard of testing (over antigen-based testing), can detect just a few virus particles — or even just one. Those small amounts of the virus are not enough to cause transmission, according to studies in the Journal of Infectious Diseases and the Lancet. Indeed, such small amounts of exposure can boost immunity in the vaccinated while causing no ill effects.
In this new phase of battling the pandemic, we should change the way we talk about covid-19 infections: Rather than discussing “cases” — meaning instances when a PCR test delivers a positive result — we should describe the viral load a person is carrying. Measuring the load size is done by determining the number of cycles required for the PCR machine to detect the virus. The more cycles used to find a virus, the lower the viral load. A positive test with a high cycle threshold, say, more than 25 cycles) — signaling a noninfectious virus — should be treated as far less worrisome than a positive test with a low-cycle threshold.
Italy and Israel are just two of the countries where a surge of infections over recent months did not cause a surge in the death rate. The case of Israel is especially instructive, because people opposed to vaccination have seized on the uptick in infections there to argue that the vaccines don’t work. But as The Washington Post’s Aaron Blake has pointed out, in Israel, where 85 percent of adults are vaccinated, cases remain at less than one-tenth of their January peak, while intensive-care admissions are at one-20th of the peak. The country has witnessed a clear decoupling between “cases” and “severe illness.”
While the United States is not experiencing decoupling of cases and severe illnesses to that degree, we are seeing a disproportionately lower number of severe illnesses per case than we did in the past. One reason instances of severe illness have not dropped even further is that the United States is far more polarized than Israel on vaccination. In communities where vaccine-skepticism is strong, there is a public health risk similar to 2020. So a full-speed-ahead vaccine push remains essential: Full FDA approval of coronavirus vaccines, which is long overdue, should help increase vaccination rates in some of these communities. So should mobile vaccinations, giving people time off work to get vaccinated and providing child care and transportation to make it easier for them to do so.
But in communities and regions where vaccination rates are high, we should be rethinking our definition of a covid-19 “case.” When we’re dealing with a vaccinated person, what we call a “case” is often instead the detection of a virus warded off by antibody and T cell immunity. (This can be true even for the delta variant, highly transmissible though it may be.) Even dead viral particles can be detected by a PCR test. This pandemic has consistently required us to rethink the meaning of the data and shift our strategy accordingly. When it comes to immune people who are asymptomatic, it’s time for us to do it again.
After a long and painful endeavor to build up an adequate testing infrastructure in this country, overtesting is an ironic problem to have. But it’s now distorting our perception of the risk of covid-19 and our ability to assess the current public health threat. Our battle is not about eliminating positive results from PCR tests; it’s about minimizing severe illness and death.
Unvaccinated individuals in the United States remain at risk. But we should not let imprecise and inflated case numbers among the vaccinated shape public policy. As we turn to the next phase of managing covid-19 in the United States, we should calibrate our guiding metrics carefully. The attention of public-health officials should remain on testing, treatment and contact-tracing for people who remain unvaccinated — and tracking hospitalizations carefully. We should certainly pay attention to breakthrough symptomatic infection after vaccination. And we need a renewed commitment to getting everyone their shots. But by now, in almost all cases, testing the asymptomatic vaccinated — and tallying cases among them — has become counterproductive.