Immunity from the Monkey-Pox vaccine appears to drop off after a few months, according to a small new study. Using samples from 45 people who were either vaccinated against or infected with mpox in 2022, researchers from Harvard Medical School found that mpox antibodies waned six to 12 months after immunization.

Two doses – which health authorities recommend four weeks apart – were better than one in the initial months after vaccination. But a year later, the immune response for people who had two shots was similar to the peak response for those who got just one dose, “which provided limited protection,” according to the study, published in the medical journal JAMA.

The findings indicate that people who were vaccinated during the global Monkey-Pox outbreak in 2022 may need additional shots to keep up their immunity, according to health experts who were not involved with the study.

Researchers said booster shots may be required for people immunized against Monkey-Pox in 2022, but larger studies are needed to confirm the findings first.