Immunity against mpox (monkeypox) may be declining over time among individuals who received the modified vaccinia Ankara-Bavarian Nordic (MVA-BN; Jynneos) vaccine, according to a study published on October 3 in the Journal of the American Medical Association (JAMA). The research suggests that additional booster doses may be required to maintain effective protection against the virus.

The study, led by Dr. Ai-ris Y. Collier and her team from the Beth Israel Deaconess Medical Center in Boston, assessed the mpox-specific immune responses in adults who had been vaccinated with either one or two doses of the MVA-BN vaccine or who had a confirmed mpox infection during the 2022 outbreak. Serum specimens were analyzed over a 12-month period to evaluate the presence and stability of mpox-specific binding and neutralizing antibodies.

Results revealed a considerable decline in antibody levels over time among those vaccinated. Participants who received two doses of the vaccine showed a peak in median antibody titers at three weeks following vaccination, but these levels had significantly decreased by the 12-month mark. Those who received just one dose experienced a similar decline, indicating that neither vaccination regimen maintained strong antibody responses over the long term. Additionally, the study found that neutralizing antibody levels, which are crucial for effective viral defense, were minimal at three months post-vaccination. By contrast, participants who had natural mpox infections maintained high titers of neutralizing antibodies three months after infection, which persisted for up to nine months.

The findings raise concerns about the durability of vaccine-induced immunity and suggest that vaccinated individuals may require booster doses to sustain protection. Given these results, health authorities may need to consider implementing booster vaccinations, especially for those at high risk of exposure, to prevent a potential resurgence of mpox infections. This study also underscores the importance of continued monitoring of immune responses in vaccinated individuals to inform future vaccination strategies and public health policies.

The study is a reminder that while initial vaccination provides a degree of protection, long-term immunity may not be guaranteed. Regular evaluations of immune responses and timely updates to vaccination protocols are crucial in ensuring sustained immunity against pathogens like mpox, particularly in communities that have already been affected by outbreaks. With these findings, booster doses could become an integral part of future vaccination strategies, providing sustained immunity and helping to mitigate the risk of future outbreaks.