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VERIFY: How do we measure immunity against COVID-19?

Between infections and immunizations, millions of people have developed a level of immunity against the coronavirus. But, how do scientists measure it?

WASHINGTON — Medical professionals have administered more than 120 million COVID-19 vaccine doses. As the country pushes toward getting everyone vaccinated, what does immunity against the coronavirus look like?


How do we measure immunity against the coronavirus?


Researchers are still learning how to best measure the level of immunity vaccinations and infections offer against future infections.


Dr. William Moss, vaccine expert from Johns Hopkins University. Dr. Bruce Walker, an immunology expert from Harvard Medical School and the Centers for Disease Control and Prevention (CDC).

What We Found:

In the case of most viruses, immunity is usually measured in the production of microscopic proteins, called antibodies, according to our experts. This can be done by infection or vaccination.

RELATED: VERIFY: Here's how much immunity you have, if you've already had COVID-19

“You mount antibodies, you clear the virus, and those antibodies stick around so that if you ever encounter that, that disease again, you'll be protected,” Dr. Walker said.

However, the case of the coronavirus is something new altogether.

“[We find] antibody levels will go up, they'll kind of peak, and they'll come down, but they'll maybe kind of plateau, or there's some slow decay over time,” Dr. Moss said.

Scientists still are not sure if that plateau or slow decay is enough to produce lasting immunity. That’s where our two experts said other microscopic parts of your immune system come into play.

One in particular scientists are now looking at are B cells. B cells create antibodies.

“Others of those convert into what are called memory B cells, which are hanging around and are ready if somebody becomes re-infected to start producing antibodies again,” Dr. Walker said.

So, when looking at immunity with COVID-19, scientists examine how long and at what level antibodies linger in the body. They also look at how long memory B cells retain a memory of what the coronavirus cells look like. There are still several other facets of the immune system that play a role in long-term immunity.

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