A coronavirus outbreak that started in China has sickened more than 82,000 people and killed more than 2,800. Cases have been recorded in 47 other countries.

Most patients seem to make full recoveries, but people who've recovered could still get the virus again in the future.

That already happened to a tour guide in Japan — she recovered from the coronavirus, then tested positive for it again three weeks later.

The antibodies that patients are producing so far don't necessarily last very long, one expert said.

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People who have gotten the new coronavirus and recovered can get it again in the future, health authorities say — the body does not become immune after infection.

On Wednesday, Japanese authorities reported the first confirmed case of reinfection. A tour guide in Osaka first tested positive for the coronavirus in late January, then was discharged from the hospital three weeks ago after showing signs of recovery. But she returned to the hospital after developing a sore throat and chest pain and tested positive for the coronavirus once again.

Zhan Qingyuan, director of pneumonia prevention and treatment at the China-Japan Friendship Hospital, warned last month that this could happen.

"For those patients who have been cured, there is a likelihood of a relapse," Zhan said in a briefing on January 31. "The antibody will be generated; however, in certain individuals, the antibody cannot last that long."

Reinfections among patients in China have been reported as well.

In total, the coronavirus has infected more than 81,000 people, 95% of whom are in China. More than 2,770 have died. (For the latest case total, death toll, and travel information, see Business Insider's live updates here.)

A risk of reinfection

The coronavirus family includes the viruses that cause SARS, MERS, and the common cold. Most cause upper-respiratory infections.

When a virus enters a human body, it tries to attach to and take over host cells. In response, our immune systems produce antibodies: proteins that recognize and remove viruses.

An illustration from the Centers for Disease Control and Prevention shows the novel coronavirus. Associated Press

That's how humans become immune to certain illnesses. Children that have contracted chickenpox, for example, are immune to the disease as adults. Vaccines are another way to develop immunity.

"With many infectious diseases, a person can develop immunity against a specific strain after exposure or infection," Amira Roess, a professor of Global Health and Epidemiology at George Mason University, told Business Insider. "Often, that person will not get sick again upon subsequent exposure to it."

But in the case of the new coronavirus, according to Zhan, doctors don't think the antibodies patients develop are strong or long-lasting enough to keep them from contracting the disease again.

"Once you have the infection, it could remain dormant and with minimal symptoms, and then you can get an exacerbation if it finds its way into the lungs," Philip Tierno, a professor at the NYU School of Medicine, told Reuters.

Coronavirus cases around the world

A medical official takes the body temperature of a child at the departure hall of the airport in Changsha, Hunan Province, as China is hit by an outbreak of a new coronavirus, January 27, 2020. REUTERS/Thomas Peter

Coronavirus cases have been reported in 47 countries beyond China.

The World Health Organization declared the coronavirus outbreak a global health emergency last month, but does not yet consider it a pandemic.

Public-health experts are urging the public — especially anyone who travels — to wash hands frequently, avoid touching one's face, and stay away from anyone who appears sick.