ACIP Endorses JYNNEOS Vaccine for Adults at Risk of Mpox Outbreaks

In a significant public health initiative, the Advisory Committee on Immunization Practices (ACIP) has recommended the JYNNEOS vaccine for individuals aged 18 years and older who are at risk for mpox during ongoing outbreaks. This announcement, made in 2023, comes amid the protracted clade IIb outbreak that began in 2022, which has seen substantial morbidity and mortality across the United States.

The recommendation follows a thorough review of the epidemiology of mpox, which is caused by the Monkeypox virus (MPXV), a zoonotic infection endemic to certain regions of Africa. Historically, mpox was primarily associated with animal-to-human transmission, but recent outbreaks indicate a shift towards human-to-human transmission, particularly among vulnerable populations such as men who have sex with men (MSM).

Dr. Agam K. Rao, the lead author of the ACIP report and a member of the CDC's Mpox Work Group, stated, "The ongoing clade IIb outbreak has evolved significantly, with cases continuing to emerge even after a year. Our recommendations are aimed at mitigating the risks associated with this outbreak."

The JYNNEOS vaccine, a live, non-replicating vaccinia virus vaccine, was approved by the FDA in 2019 and has been shown to provide cross-protection against MPXV. According to a study published in the New England Journal of Medicine in 2023, the two-dose series of JYNNEOS has demonstrated a vaccine effectiveness ranging from 66% to 89% against diagnosed mpox infections (Deputy et al., 2023).

The ACIP's recommendation is particularly timely, as the CDC had previously issued interim vaccination guidance based on the evolving epidemiology of mpox. The clade IIb outbreak has raised concerns about the potential for further spread, especially in urban settings where close contact is common. As of 2025, the United States has reported approximately 35,000 mpox cases, leading to a reevaluation of vaccination strategies and public health messaging.

Experts emphasize the importance of vaccination as a preventive measure. Dr. Faisal S. Minhaj, a pharmacy expert and contributor to the ACIP report, commented, "Vaccination is crucial in controlling the outbreak and preventing further cases. We must ensure that those at risk have access to the vaccine and understand its benefits."

In light of the ongoing outbreak, the ACIP has outlined specific risk groups for the JYNNEOS vaccine, including MSM who have multiple sexual partners, those with recent sexually transmitted infections, and individuals attending large public events in areas with known mpox transmission. Vaccination is not routinely recommended for healthcare personnel during mpox outbreaks due to low incidence rates among this group.

The public health implications of the ACIP's recommendations are profound. Increasing vaccination coverage will not only help limit the scope of the current outbreak but also prepare the health system for potential future outbreaks. The CDC anticipates reassessing the need for ongoing vaccination as the outbreak evolves.

As we move forward, public health authorities will continue to monitor the situation closely. Future research is also planned to evaluate long-term vaccine effectiveness and the potential need for booster doses, particularly among immunocompromised individuals. The evolving epidemiology of mpox underscores the necessity for adaptive public health strategies and continued vigilance in vaccination efforts.

In summary, the ACIP's endorsement of the JYNNEOS vaccine for adults at risk of mpox during outbreaks is a pivotal step in addressing the challenges posed by the ongoing clade IIb outbreak. The emphasis on targeted vaccination strategies and the involvement of at-risk populations will be critical in controlling this public health threat.