A study led by researchers at Beth Israel Deaconess Medical Center (BIDMC) has demonstrated that mpox antibody levels declined rapidly and nearly returned to baseline six to 12 months after patients received the mpox vaccination. The findings, published in JAMA, suggest that protective immunity may have waned in previously vaccinated individuals and that boosting may be required to maintain robust protection.

"The WHO declared the current mpox outbreak in the Democratic Republic of the Congo a public health emergency," said corresponding author Dan H. Barouch, MD, Ph.D., director of the Center for Vaccine and Virology Research at BIDMC. "It is therefore important to assess the infection risk for individuals who were vaccinated against the disease during the 2022 outbreak."

Previously known as monkeypox, the 2022 mpox outbreak marked the first time the virus spread widely across multiple countries beyond Africa. Spread primarily through close skin-to-skin contact, especially during sexual activity, mpox manifests as fever, swollen lymph nodes, and painful rashes or sores.

To contain the outbreak, public health officials prioritized vaccination for populations at higher risk of exposure, including people who have new or multiple sexual partners, especially men who have sex with men; health care workers and laboratory personnel; and people who have traveled to a community where mpox has been identified.

Barouch and colleagues assessed mpox-specific immune responses for 12 months in 45 individuals who were vaccinated during the 2022 mpox outbreak. The team performed an observational study in adults who received either one or two doses of the MVA-BN vaccine (known by the brand name Jynneos) or who had a confirmed diagnosis of mpox infection, assessing serum antibody and T cell responses at baseline, three weeks, three months, six months, nine months, and 12 months following vaccination. They observed that vaccination generated serum mpox antibodies that largely waned six to 12 months after vaccination.

"Our study highlights the importance of completing the recommended two-dose mpox vaccine, whether subcutaneous or intradermal, to boost immunity—regardless of the time between doses," said lead author Ai-ris Yonekura Collier, MD, co-director of the Clinical Trials Unit at BIDMC. "In this mpox outbreak, ensuring broad access to the full vaccine series is crucial."

Serum mpox antibodies correlated with protection against mpox challenge in preclinical studies. Larger human studies are needed to confirm generalizability and to assess vaccine efficacy over time, Barouch said.