While most patients who contract the coronavirus 2019-nCoV eventually make a full recovery, they don’t walk away from the encounter immunized against the disease, as one might expect after a viral infection.

Rather, Business Insider reports that you can theoretically catch the coronavirus multiple times, creating an unusual challenge for health officials trying to contain the outbreak.

The underlying idea behind a vaccination — or even “chicken pox parties” — is that exposure to a virus will trigger the immune system to generate antibodies that will shield that person from that virus in the future. But according to Chinese health officials, the antibodies created after a 2019-nCoV infection aren’t always strong enough to keep patients from getting sick again.

“For those patients who have been cured, there is a likelihood of a relapse,” Zhan Qingyuan, the director of pneumonia prevention and treatment at the China-Japan Friendship Hospital, said during a Friday press conference.

“The antibody will be generated,” he added. “However, in certain individuals, the antibody cannot last that long.”

Because some patients could get sick multiple times, it will prove even more difficult to track and contain the viral outbreak — which has already spread to and killed more people than did the entire SARS outbreak of the early 2000s.