Out of 491 patients, six people or 1.2 percent experienced the infection, researchers said.
The six patients all have mild cases of autoimmune inflammatory rheumatic diseases and were young, though the infection is generally more common in those over the age of 50.
"That is why we reported on it," Dr. Victoria Furer, the lead author, told the outlet.
Five of them developed herpes zoster after the first dose and the sixth got it after the second.
But it’s still unclear whether the vaccine caused the cases of herpes zoster.
"We cannot say the vaccine is the cause at this point," Furer told the outlet. "We can say it might be a trigger in some patients."