Fauci says he's not going to waste his time with an antibody test, and neither should you

• In the weeks after a COVID-19 infection or vaccine, neutralizing antibodies can wane.
• Other forms of immune protection are still ramping up in the body, standing guard against COVID-19.
• Fauci says antibody tests are a crude way to assess vaccine protection. Better answers are on the way.

Dr. Anthony Fauci has no idea whether he has any detectable virus-fighting antibodies against COVID-19. And he doesn't care to find out, either.

Fauci, who's been fully vaccinated for five months, assumes his vaccine protection will fade, and that he will need a booster shot.

"You don't want to assume that you're going to have indefinite durability of protection," he told Insider in a recent phone call.

But he won't rely on antibody tests to tell him when another shot is necessary.

"If I went to LabCorp or one of those places and said, 'I would like to get the level of anti-spike antibodies,' I could tell what my level is, if I wanted to. I didn't do it," he said.

Instead, Fauci will wait for two signals.

One: rising rates of breakthrough infections in vaccine trial participants who got their first shots in early 2020. The second: convincing laboratory data telling us how our vaccine protection may be waning.

Antibody tests are crude

Fauci isn't completely blasting antibody tests.

To measure immunity, "the most easy and convenient [thing] to do is to measure the level of antibodies in the sera," Fauci said.

The blood tests are a crude shortcut to help answer a complicated question: how well will we fight a future COVID-19 infection?

However, they're not foolproof indicators of protection, especially after vaccination.

The FDA advises against using antibody tests to check your COVID-19 protection status because the results can be misleading (they were designed to detect prior natural infections, not immunity). Some antibody tests don't even target the same viral protein the vaccine does (that's why Fauci said he'd only ask for an 'anti-spike' test, if he ever wanted one).

How we really measure COVID immunity

Though a sick person's body will initially pump tons of antibodies into their blood to clear an infection, the true masters of long term viral immune defense are B-cells and T-cells, which are produced and dispatched from the bone marrow, like a cache of disease-fighting army reserves.

"If we had high levels of antibodies in our blood to every pathogen we were exposed to, our blood would quickly just become a sludge of antibodies," said Dr. Rachel Presti, medical director of the Infectious Diseases Clinical Research Unit at Washington University in St. Louis.

But while B-cell and T-cell responses are supremely important pieces of the body's long-term immunity equation, they're "much more complicated to measure on a routine basis" than antibodies circulating in our blood, Fauci said.

Many immunologists have been saying this for months: a body's response to vaccination is more complex than consumer antibody tests can properly assess.

Scientists are trying, though.

In a recent study (co-authored by Presti, which was published in the journal Nature on Monday) 14 Pfizer-vaccinated patients underwent "fine needle aspiration" - using a tiny needle to pull a sample of cells out of their armpits.

Then, researchers tested those samples to gauge the patients' B-cell responses to the original COVID-19 spike protein. Their results suggest Pfizer's vaccine armor remains robust for at least 12 weeks after a second shot, and possibly for much, much longer.

B-cells are also, likely, our armor against emerging variants. Immunologist Shane Crotty from the La Jolla Institute for Immunology told Scientific American: "Memory B cells are your immune system's attempt to make variants of its own."

We won't rely on blood tests

Antibody tests will still be one tool used to study how well vaccines work long term in the "literally tens of thousands of people" who were in the COVID-19 vaccine trials, Fauci said.

But it won't be routine for everyone.

Likely, studies assessing B-cells and T-cells, too, will show that elderly people and those with underlying conditions need a boost first.

Then, Fauci predicts, COVID-19 shots will operate more like tetanus boosters: a clinician may recommend another shot to you based on your age, health, and vaccine schedule.

"You don't have to all individually get a blood test," Fauci said.