Can at-home Covid tests detect variants? How the rapid tests work

Medical Watch

It’s being called a critical next phase in managing the pandemic. President Biden plans to supply 500 million kits to Americans in January.

Rapid tests have been in use for months in schools and the workplace. And in the weeks and months to come, they’ll will be a staple in your home medicine cabinet.

Dr. Thomas McDade is an anthropologist at Northwestern Medicine.

“If you do it right, they are highly accurate and very good at detecting infections that can be transmitted,” he said.

But will the at-home versions hold up to the omicron variant that’s figured out a way to evade some the most sensitive tests? Even lessened vaccine efficacy with changes to the spike protein?

Unlike PCR testing that looks for actual DNA of SARS-CoV-2, rapid tests directly capture pieces of the virus – antigens. The most reliable tests detect what’s called the nucleocapsid, an internal component of the viral particle.

“That does not change as much with variants like omicron, so rapid tests that are designed to capture the nucleocapsid are much less vulnerable to evasion by these variants like omicron,” McDade said.  

Think of the process like a common pregnancy test.

“You swab your own nose or swab a child’s nose, and you put the tip into a solution or a cartridge or card that carries the solution through a test strip,” McDade said. “And if it comes up positive, there will be a line that shows the presence of the virus in the sample.”

It takes about 5 to 15 minutes to work. False positives are rare, but false negatives?

“You can get false negative results because the antigen tests require more virus to detect. They are not as sensitive as PCR tests. But the good news is if you have a negative result and you are in fact positive, the amount of virus in your sample is so low that you are probably not as infectious to other people, assuming you did the test correctly,” McDade said. ”We want to keep each other safe, but we also want to keep our kids in school and go to work. So this is an important tool to do that.”

Right now, at-home kits are difficult to find – demand is high before holiday gatherings. There are several rapid test manufacturers including Abbott based here in Chicago.

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