DETROIT – Officials are looking into reports that the coronavirus (COVID-19) is “reactivating” in some patients who were thought to have recovered, causing them to test positive for a second time.

It’s one of the biggest questions in the battle against the coronavirus: Once you recover from the illness, are you immune from catching it again? The answer to that question has gotten even more complicated than experts previously thought.

Officials in South Korea have reported about 100 patients thought to have recovered from COVID-19 have tested positive for the virus again.

Experts with the World Health Organization said they are investigating the reports.

With many viruses, once someone is exposed and successfully fights them off, the body develops antibodies that protect from that illness. How long that immunity lasts varies from virus to virus.

Experts believe people who recover from being infected with the SARS-CoV-2 virus should have some degree of immunity, but the virus is so new they don’t know for sure.

South Korea’s Centers for Disease Control and Prevention suggested that the virus might have been “reactivated” in recovered patients who later tested positive.

Experts said another possibility is that the test is detecting lingering strands of the virus’ genetic material, not a true reactivation.

But another theory is that some of the patients were reinfected.

More studies are needed to determine the truth. Results could have major implications for nations relying on antibody tests to determine who is safe to return to work. It could also affect the development of a vaccine.

A successful vaccine would need to generate an immune response that’s strong enough and lasts long enough to offer meaningful protection.

Different targets could generate different levels of response, but determining that will also take time.

There is some research underway in China that could help answer some of the questions. This is a key issue in how we’ll be able to fight this virus in the future and how long it will continue to be a threat.