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April 4, 2020, 9:01 a.m. EDT

Hundreds of different coronavirus tests are being used — which is best?

The FDA loosens the rules

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By David Pride

When it comes to testing in the United States for coronavirus and the COVID-19 illness


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A doctor administers a coronavirus swab test at a drive-through testing center in the Bronx.

it causes, the situation is about as messy as it gets.

The U.S. went from having no tests, or assays, available for COVID-19 diagnostics to having multiple different tests available in a span of just a few weeks. Today more than 230 test developers have alerted the Food and Drug Administration that they are requesting emergency authorization for their tests; 20 have been granted. And 110 laboratories around the country, including my own , are also using their own tests. Having this number of diagnostic tests available to detect a single virus in such a short time frame is unprecedented.

Which tests are good and which tests are bad isn’t immediately apparent. According to a March 30 press release from the FDA, “ The FDA revised the process to allow labs to begin testing prior to FDA review of their validation data. This policy change was an unprecedented action to expand access to testing.”

The guidance the FDA provides to test makers requires laboratories provide some evidence of their assay’s performance and consistency in results. It also ensures that reasonable thought is put into assay design. Assays meeting these requirements may then be permitted for clinical use prior to receiving approval by the FDA.

I am a physician scientist who studies viruses in my research laboratory and directs a clinical microbiology facility for a large hospital system. Since COVID-19 made it to the U.S., laboratory directors like me haven’t had a spare moment to focus on anything other than developing tests to respond to this pandemic.

There’s still a lot to learn

SARS-CoV-2 is the virus that causes the disease. It is a novel virus from the coronavirus family that was first identified in November 2019 in Wuhan, China . Like other viruses, this one is believed to have first infected animals and then jumped over to humans . Because of their zoonotic origins , these viruses are often ill-suited to spread from person to person. What makes COVID-19 so different is it’s readily spread between people, which lies at the heart of the current pandemic.

There is a lot that we just don’t yet know about COVID-19.

For example, for most respiratory viruses we develop antibodies that protect us from getting infected by them again. This is referred to as immunity. We assume that we’ll develop immunity from having been exposed to COVID-19 infections, but it hasn’t exactly been around long enough for us to know this for certain. Will this virus mutate so that our immunity won’t work? Will this virus become seasonal , much like the flu? Only time will tell.

Developing a test to detect this novel virus has been at the center of the efforts in the U.S. to combat its spread. If infected people can be quarantined early , they are much less likely to transmit it to others.

But right now there are at least 22 different COVID-19 tests on the U.S. market, not including at least 110 developed by individual laboratories across the country. So you many be wondering: Why do we need so many?

Why so many different tests?

Most of the available tests are based on collecting the virus’s RNA (ribonucleic acid) and converting it to DNA (deoxyribonucleic acid). This is the easy part of test development because all these tests use the same basic methods. The next step is making many millions or billions of copies of the DNA so that it can be detected. This is where most tests differ. COVID-19 is a large virus with many different genes that can be used to detect it . While one test may target one or more virus genes, another test may target a completely different set of genes.

The World Health Organization developed testing specifications for COVID-19 in January 2020. The U.S., led by the Centers for Disease Control and Prevention, developed separate testing specifications in early February 2020. The CDC started off as the single testing center for the U.S., but as demand rose, they distributed their test to public health laboratories across the country. This first CDC test probed the sample for three short sections of the virus’s genetic material .

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