Too Long, Didn't Read: It's definitely screening out people more likely to be ill w/COVID but it won't catch asymptomatic carriers.
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Let's look at a very nicely done study that screened both people more likely to have the disease (based on travel patterns and symptoms) versus the general population.
In the Icelandic study noted above, two sets of people were screened.
The first ("high risk") group was considered to be more likely to be infected with COVID-19 due to
1. Travel patterns (to/from high risk areas) and
2. Symptoms (including fevers),
13% were found to be COVID - positive
The second group was a sampling of the general population.
Researchers found that, among those self-reporting as symptomatic, only 0.6% and 0.8% were found to have COVID.
What does that mean in practical terms? For everyone who reported feeling symptomatic, it would take screening (roughly speaking) hundreds of symptomatic people before you found one positive case (or possibly positive for COVID-19 since your'e only screening by temperature). In other words, many of those who were symptomatic were ill due to some other illness.
You may be wondering if the no-contact thermometers are any good?
Yes.
Some caveats however,
A person's temperature varies significantly throughout the day.
Body temperature when we're ill also varies throughout the day. We have all experienced waxing and waning fevers over the course of a day when ill.
Nowadays, given the concerns for COVID-19 infection, it seem reasonable to assume that symptomatic people are going to avoid entering places in the first place.
Finally, fever feelings do not necessarily correlate to an actual, current fever.
Given all of this, you would likely have to screen thousands of people before you found one positive COVID carrier.
In medicine we call that kind of test completely worthless.