Report: Mpox infections after 2 doses of Jynneos rare

mpox vax


Two doses of Bavarian Nordic’s Jynneos vaccine offer almost complete protection against mpox, according to a new report published today in Morbidity and Mortality Weekly Report. Also today, MMWR published an update on clade II mpox cases in the United States, showing cases have been consistent since October 2023, with most cases occurring in unvaccinated people.

In the first study, on Jynneos, the authors say that despite perceptions that now, 2 years after the global mpox outbreak began (primarily among men who have sex with men [MSM]), cases are rising among the previously vaccinated, there is actually evidence that  “persistent vaccine-derived immunologic response among persons who received the 2-dose vaccine series exists.”

In May 2023, a cluster of mpox cases of occurred among vaccinated MSM, leading people to think vaccine efficacy was waning. 

"Public perception of an increase in monkeypox virus (MPXV) infections among fully vaccinated persons during 2024 has further fueled concerns about the 2-dose series,” the authors said. 

The authors examined health records for 32,819 probable or confirmed US mpox cases reported to the Centers for Disease Control and Prevention from May 11, 2022, to May 1, 2024, and found a total of 24,507 (75%) occurred in unvaccinated persons. There were 271 cases (0.8%) among persons who were fully vaccinated. 

Of those 271 cases, only 51 (19%) occurred during 2024. Mpox cases among fully vaccinated persons occurred a median of 266 days after receipt of the second vaccine dose, the authors said. 

Overall, fully vaccinated persons had a 0.1% infection rate. 

The number of breakthrough infections did not comprise a significant proportion of infections, including during 2024.

“The number of breakthrough infections did not comprise a significant proportion of infections, including during 2024,” the authors said. “With only one in four eligible U.S. persons fully vaccinated, clinicians and public health authorities should continue to focus efforts on increasing vaccine coverage.”

US averaging 59 reported cases per week

In another report, researchers show that from October 1, 2023, through April 30, 2024, the United States has averaged 59 cases of mpox each week, mostly among unvaccinated people. 

The weekly average is down significantly from a peak of 3,000 cases per week in summer 2022. 

Current cases are mostly reported among males (94%), 90% of whom identify as gay or bisexual. The average age of new case-patients is 34 years, and 34% identify as Hispanic, 32% as White, 25% as Black, 3% as Asian, 2% as multiracial, and 4% as another race.

Since October 2023, five US patients with mpox have died, the authors said.

"The current average of 59 reported cases per week represents a fifty-five-fold reduction, compared with the peak of 3,274 cases reported during the week beginning July 31, 2022 (the peak outbreak week); levels have remained stable since October 2023," the authors concluded.

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