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For the first time, experts have been able to confirm that a former COVID-19 patient has been reinfected by the coronavirus.

The news suggests that immunity to the coronavirus could only last several months — something that scientist have suspected for a while, but haven't been able to confirm so far using rigorous testing, according to The New York Times.

A new study published in the journal Clinical Infectious Diseases today reports that a 33-year-old man showed mild symptoms the first time he was infected, and no symptoms the second time around.

Interestingly, the patient was infected by two genetically different strains of the coronavirus. The second infection was confirmed after the patient traveled back to Hong Kong from Spain via the UK.

"Our results prove that his second infection is caused by a new virus that he acquired recently rather than prolonged viral shedding," Kelvin Kai-Wang To, clinical microbiologist at the University of Hong Kong, said in the statement.

"This is no cause for alarm — this is a textbook example of how immunity should work," Yale School of Medicine professor Akiko Iwasaki, wrote in a Monday tweet. "While immunity was not enough to block reinfection, it protected the person from disease."

Iwasaki also noted that the patient had detectable antibodies after reinfection, but "more studies are needed to understand the range of outcomes from reinfection."

"What I think is really important is that we put this into context," Maria Van Kerkhove, the World Health Organization's technical lead for coronavirus response, said during a media briefing in Geneva on Monday, as quoted by CNN.

"Even if this is the first documented case of reinfection, it is possible of course because with our experience with other human coronaviruses, and the MERS coronavirus and the SARS-CoV-1 coronavirus, we know that people have an antibody response for some time but it may wane," Van Kerkhove added.

The length of the immune response to the virus could eventually inform how long vaccines will be effective for, as STAT News points out. Some patients might end up needing a booster dose.