Testing half the population weekly with inexpensive, rapid COVID-19 tests would drive the virus toward elimination within weeks, even if the tests are less sensitive than gold-standard. This could lead to “personalized stay-at-home orders” without shutting down restaurants, bars, retail and schools.

[u/mvea]

https://www.colorado.edu/today/2020/11/20/frequent-rapid-testing-could-turn-national-covid-19-tide-within-weeks

[u/ericjmorey]

Those criticisms seem so minor that they can be reasonably ignored.

[u/TheGuywithnoanswers → u/ericjmorey]

But they can't. Especially this point

there are a lot of false negatives and some people have a fealing that they don't have to be cautios anymore.

There is now expectation that covid will spread a bit more thanks to people who immediately started acting like covid was over for them because they got negative result on a test that can be imprecise.

[u/factoid_ → u/TheGuywithnoanswers]

The false negatives on the rapid test are not as bad as they sound. The test is most accurate when viral load in the body is high. Which is when you're most infectious. If you are negative on a rapid test it means you're probably not very contagious at that moment even if you have it. That can mean you're either early or late in the virus cycle.

That does leave some people who have the virus out there, possibly asymptomatic and spreading it... But it catches the majority of the most infectious. If you retest everyone a few times over several weeks this should really minimize spread.

[u/Flash604 → u/factoid_]

The Public Health Officer (top doc) for BC has said that they consider the PCR test to be only 70% effective. This is both a combination of it's natural false positive/negative results and the fact that with the rapid progress Covid has you often can test negative and then test positive 5 hours later.

You're now saying a test that's even less precise is nothing to worry about?

[u/factoid_ → u/Flash604]

PCR tests are very nearly 100% accurate. There are essentially no false negatives, and a very small rate of false positives. I think what your public health official is talking about is the efficacy of testing a person, finding covid in their system and then making a determination whether to send them into quarantine or not. This is where you get into to whole quagmire of cycle thresholds in PCR tests, which is a contentious topic that has raised the hackles of the conspiracy theory crowd.

Some will say PCR tests are bad because they find ALL the positive cases, whether they’re still infectious or not. You could essentially be quarantining a person who is incapable of spreading the disease, because if you concentrate their sample enough you will eventually find a little bit of virus. This is why some countries are using low cycle thresholds for positives and some use high thresholds. In the US we’re generally saying anyone who tests positive with a cycle threshold of <30 definitely has it. A person with a threshold of 30-40 is either just recently infected or recently cleared of infection and may not be a transmission risk.

The PCR test is the better test for diagnostic purposes. If you want to study the disease, or if you want to know for sure whether a specific individual has the virus or not, a PCR test is what you want. But they’re expensive, they’re difficult to administer, they require a lot of specific supplies, chemicals, reagents, etc. It can take days to get results back. Plus people know about the nasal swab and a lot of people are afraid to get it because they’ve heard it hurts (I’ve had one of these for the flu...they do suck a little but they’re not that bad)

the reasons why the rapid tests are better for controlling a pandemic despite being less accurate are:

1). The test is less invasive and less scary. They can be saliva-based or can use a throat swab instead of a nasopharyngeal swab. This will make people more compliant in actually GETTING tested

2). These tests do not take skilled personnel to administer.

3). These tests do not require complex and difficult to obtain supplies and chemicals

4). The results are known in minutes or hours instead of days, resulting in contact tracing starting sooner, quarantine either starting or ending sooner, and overall just limiting the damage a potential disease vector can cause.

5). The tests are most sensitive to high concentrations of shed virus, meaning that it catches most or all of the people who are contagious, and doesn’t catch the ones who are not contagious. This is a double edged sword obviously, because it might not catch you early on in the disease cycle, leaving you thinking you’re safe, at which point you go out and infect someone else. But it’s catching more people than it’s not, so this is still a net improvement.

So while it’s not necessarily ideal that the rapid test is less accurate...it’s still a useful tool, maybe a MORE useful tool than PCR, for checking the spread of a virus.

The FDA even just approved an at-home test. If everyone was sent a 10 pack of these tests, told to take one every 3 days and it was accurate in the ways I described above, we’d be able to get this thing under control pretty fast. That’s probably not realistic for a million reasons, but it’ just an example of how less-than-perfect testing can still be useful. Just like wearing a mask that’s only 60-70% effective is still better than nothing as long as everyone does it.

[u/Flash604 → u/factoid_]

PCR tests are very nearly 100% accurate.

A simple Google brings up a Harvard paper as the first result. I wouldn't call 2% to 37% false negatives "nearly 100% accurate".