I’m a nurse. My husband recently asked a great question, which I couldn’t answer. We are both vaccinated, and he wondered if exposures to the coronavirus still circulating in our community would act as boosters that could strengthen our immunity. Is there any evidence of this?”

— Anne in Maine

Yes, absolutely.

After a coronavirus vaccination, exposure to the circulating virus will trigger an immune response to protect against infection and at the same time will also boost your immunity, said Monica Gandhi, an infectious-diseases expert at the University of California at San Francisco.

To be more specific, the coronavirus vaccines prime the immune system to recognize the spike protein — the proteins found on the surface of the coronavirus — by producing antibodies and memory cells. These memory cells are known as B cells and T cells.

When the coronavirus is later detected in the body, the immune system stimulates these memory cells to respond — B cells start making more antibodies, while T cells work to attack and kill.

This immune response not only protects against the current exposure but also strengthens the immune system to guard against infections in the future, Gandhi said.

Research published last week in the journal Nature found that memory B cells produced in response to the messenger RNA vaccines are stored in the body and increase over time, building stronger immunity. There is also emerging evidence these cells will respond when they see future variants.

All of that said, just because you are vaccinated and (absent some underlying health issue) your immune system is ready and willing to fight off infection, that does not mean you should be careless or knowingly expose yourself to the virus. Although severe breakthrough infections are rare, they do occur. Out of more than 150 million people who are vaccinated in the United States, there have been more than 4,000 reports of breakthrough infections that resulted in hospitalization or death, according to data from the Centers for Disease Control and Prevention.

So even though your immune system is staying fit, Gandhi said “staying safe is still important.”

— Lindsey Bever