Scientists have reported that a 33-year-old man has been infected twice by different versions of the coronavirus a few months apart. The man was hospitalized with the virus on March 29 and tested positive again at Hong Kong airport on August 15, after returning home from a trip to Spain.

According to the Independent, he suffered no symptoms the second time around and experts cautioned that while no conclusions can be drawn from one case, the incident is concerning. Researchers reporting the case in the medical journal Clinical Infectious Diseases, said:
“Since the immunity can be short lasting after natural infection, vaccination should also be considered for those with one episode of infection.”

According to NBC News, early research in coronavirus antibodies showed that their protection waned after a few months. Researchers at King’s College London analyzed the blood of infected patients and healthcare workers and found that the levels of protective antibodies peaked about three weeks after the first symptoms appeared. However, those antibodies were found in only 17% of the patients three months later.

According to The Daily Caller, in some patients, the antibodies were virtually undetectable.

“People are producing a reasonable antibody response to the virus, but it’s waning over a short period of time and depending on how high your peak is, that determines how long the antibodies are staying around,” said Dr. Katie Doores, one of the lead authors of the study.

The new research suggests that people can get repeatedly infected with the virus, much like they do with the common cold. It also suggests limitations for the effectiveness of a potential vaccine, Doores said.

Dr. Anthony Fauci, head of the National Institute of Allergy and Infectious Diseases, has said that immunity to other coronavirus, including the common cold, usually lasts only three to six months.

“It may be completely different with this coronavirus,” he said, according to NBC News. “It may be that people induce a response that’s quite durable. But if it acts like common coronaviruses, it likely is not going to be a very long duration of immunity.”