Your Coronavirus Antibodies Are Disappearing. Should You Care?

A mild illness may trigger production of only a few antibodies, and a severe one many more. The vast majority of people who become infected with the coronavirus have few to no symptoms, and those people may produce a milder immune response than those who become severely ill, Dr. Havers said.

But even a minor infection is often enough to teach the body to recognize the intruder.

After the battle ends, balloon-like cells that live in the bone marrow steadily pump out a small number of specialized assassins. The next time — and every time after that — that the body comes across the virus, those cells can mass-produce antibodies within hours.

The mnemonic response grows stronger with every encounter. It’s one of the great miracles of the human body.

“Whatever your level is today, if you get infected, your antibody titers are going to go way up,” said Dr. Michael Mina, an immunologist at Harvard University, referring to the levels of antibodies in the blood. “The virus will never even have a chance the second time around.”

A single drop of blood contains billions of antibodies, all lying in wait for their specific targets. Sometimes, as may be the case for antibodies to the coronavirus, there are too few to get a positive signal on a test — but that does not mean the person tested has no immunity to the virus.

“Even if their antibodies wane below the limits of detection of our instruments, it doesn’t mean their ‘memory’ is gone,” Dr. Mina said.

A small number of people may not produce any antibodies to the coronavirus. But even in that unlikely event, they will have so-called cellular immunity, which includes T cells that learn to identify and destroy the virus. Virtually everyone infected with the coronavirus seems to develop T-cell responses, according to several recent studies.