MPOX TRACKER

The World Health Organization’s decision to uphold mpox as a public health emergency of international concern has renewed scrutiny of vaccination strategies, particularly the need for a third (booster) dose of the JYNNEOS vaccine. France’s High Authority for Health has taken a proactive stance, recommending a booster for individuals vaccinated in 2022, emphasizing that it enhances antibody persistence—especially for those who are immunocompromised or have no prior infection.

In contrast, the U.S. Centers for Disease Control and Prevention (CDC) has adopted a more conservative approach. As of June 2025, the CDC maintains that the two-dose series remains effective, noting that breakthrough infections are rare and generally mild. With over 1.2 million doses administered across the U.S., current guidance does not recommend a third dose for the general population.

This position may soon be tested. A preprint study published on June 6, 2025, evaluated the safety and immunological durability of the MVA-BN (JYNNEOS) vaccine across African populations. Results indicate that the vaccine induces sustained immune memory up to five years post-vaccination. However, the study also found that adding a third dose significantly increases reactogenicity compared to the initial two-dose regimen. Importantly, only one confirmed breakthrough infection was reported among participants.

Given mpox’s continued spread to 122 countries—115 of which had no prior reported cases—the global risk landscape is shifting. As Clade II mpox remains concentrated among unvaccinated individuals or those who received only one dose, especially in the U.S., public health authorities must reassess vaccination guidelines.

Emerging data may eventually tip the balance toward booster adoption, particularly for high-risk groups. Until then, the CDC's current stance reflects a careful trade-off between immunological benefit and tolerability. A nuanced, data-driven strategy will be key as the outbreak evolves.