The results “call for caution regarding antibody-based ‘immunity passports,’ herd immunity, and perhaps vaccine durability,” the California authors write.

That’s true, Creech said, but other parts of the immune system also help confer protection. Besides churning out antibodies, B cells develop a memory so they know how to do that again if needed.

“They would get called into action very quickly when there’s a new exposure to the virus. It’s as if they lie dormant, just waiting,” he said.

Other white blood cells called T cells also are better able to attack the virus the next time they see it, Creech said.

Although circulating antibodies may not last long, what we need to know is if and how people remake antibodies if exposed to the coronavirus again and if they protect against another infection, Alison Criss, an immunologist at the University of Virginia, wrote in an email. “We also need to know if there is a protective T cell response” that reappears.