Despite rolling back key guidance on coronavirus safety measures like face masks, the Centers for Disease Control and Prevention still recommends businesses and employers consider daily symptom and temperature checks. Since COVID-19 is far from over in the United States, we must make better-informed decisions about what type of prevention practices work.
And it’s time to remove practices—like checking temperatures and symptoms—that do not work.
Why was fever screening implemented? Earlier in the pandemic, when the spread of COVID was not as well understood and highly accurate tests were not as readily available, it was thought that fever was a telling symptom of COVID-19. However, we now know that people can have COVID-19 with many different symptoms—or with a complete lack thereof.
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A scientific review of 22 peer-reviewed studies last fall found that if temperature checks were used to screen 100 people with COVID-19, between 31 and 88 of those with infection would be missed—and up to 10 people without infection would be falsely identified as possibly infected. Data from another study also suggested that temperature screening can miss over 75 percent of those with infection.
To better understand why temperature checks are theater, it’s worth revisiting what a fever actually is. The origin of fever defined as a body temperature of ≥100.4°F (≥38.0°C) is commonly traced to the 1868 work by Carl Reinhold August Wunderlich, Das Verhalten der Eigenwärme in Krankheiten (The Course of Temperature in Diseases). In this context, it amounts to an increase in body temperature and can have many causes, including infection, heat exposure, auto-immune disease, stroke or heart attack, and cancer.
Unlike the skin, which can be warmed or cooled by the local environment, the core body temperature, generally defined as the temperature of blood in a deep vein near the heart, is what is important to measure to determine the body’s internal environment. Prior research has suggested that infrared skin surface thermometers—the ones most visible in this era of temperature checks at the door—do not reliably predict core body temperatures.
Symptom screening is also ineffective. The aforementioned review also found that if symptom screening was used on 100 people with COVID-19, the measures would deem 40 to 100 of those with infection as healthy. Data collected from an outbreak in a long-term skilled nursing facility found that when tested for COVID-19, 23 of 76 (30.3 percent) residents had positive test results, but 13 of 23 (57 percent) infected people reported they had no symptoms on the day of testing or prior.
In November, the CDC published a study that assessed temperature and symptom screening efforts at U.S. airports, finding that the observed number of identified cases was 1 per 85,000 travelers screened. The authors remarked that those real-world findings were consistent with scientific models that suggest many infected travelers would be undetected by airport screening.
So the case is strong that temperature and symptom checks are a weak means of preventing COVID-19 spread. And now, given the decreasing number of new infections and the rising proportion of those vaccinated, it is critically important to remove ineffective means of infection control and focus on measures that work.
Currently, temperature screening is recommended federally, as well as in 22 states, and symptom screening is recommended federally as well as in 38 states, Washington, D.C., and Puerto Rico. It might seem like as long as people are dying and getting infected, every safety measure is worthwhile. But the problem is that normal temperature and symptom screening results can create a false sense of security. Additionally, activities to conduct screening are costly in terms of staff’s time performing the checks, equipment, equipment maintenance, people’s time undergoing checks, software, and the costs of false-positive (and false-negative) results.
As vaccination increases, the main driver of the continued spread of COVID-19 in the U.S. is unvaccinated people—whether because they refuse to get shots or otherwise—with asymptomatic or unrecognized infection. Vaccinated people, on the other hand, appear to be highly unlikely to contribute to the spread of new infections. Since the goal of screening measures is to keep those infectious away from those susceptible, vaccination reduces the pools of both—those infectious and those susceptible—making routine screening even less useful.
In fact, if we feel we must continue screening employees, visitors, and others entering certain venues, we should be screening people for vaccination status. Some large venues, like baseball stadiums, have already begun to use vaccination status as a means for admittance to certain sections. Despite the concern by some privacy advocates—and, for very different reasons, a number of conservative politicians—over “vaccine passports,” they make a lot of scientific sense.
With more evidence about the benefits and costs of various interventions, COVID-19 control activities should continue to be updated as the epidemic and control measures improve. Resources should be redirected from ineffective means of epidemic control, like temperature or symptom screening, to ones that are now proven to be useful such as ventilation, vaccination, and case-finding through targeted testing and surveillance.
