"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," he told Insider. "I didn't do it."
According to Insider, Fauci said he’d instead wait for two broad signals: rising rates of breakthrough infections in people who took part in vaccine clinical trials in early 2020 and laboratory data that shows how vaccine protection may be waning.
Fauci, the chief medical adviser to the White House and the director of the National Institute of Allergy and Infectious Diseases, was publicly vaccinated with the Moderna vaccine, getting his first shot Dec. 22.
He said he thinks the vaccine protection will fade with time and that he’ll eventually need a booster shot.
"You don't want to assume that you're going to have indefinite durability of protection," he told Insider.
Experts have said antibody tests are not a good way to measure that protection. They’re designed to determine whether somebody has had the virus in the past. Insider pointed out that some antibody tests don’t target the same protein that the vaccine does.
The FDA agrees that people should not rely on antibody tests to find out how their vaccine is holding up. On May 19, it put out a statement saying that “antibody tests should not be used at this time to determine immunity or protection against COVID-19 at any time, and especially after a person has received a COVID-19 vaccination.”
As more people are vaccinated, they’re also wondering whether they’ll need booster shots.
But nobody knows for sure how long the vaccine protection lasts.
In April, Moderna and Pfizer said their vaccines offer more than 90% efficacy after 6 months. A recently published study said those vaccines may provide low-level protection for up to a year.