Mpox Vaccine is 99.2% Efficacious Against Infection


The vaccine, Jynneos (Bavarian Nordic), is an FDA-approved vaccine for mpox, and is now available for commercial purchase in the United States.

Mpox under the microscope.  Image credit: CDC

Mpox under the microscope.

Image credit: CDC

In the latest MMWR published today, investigators report the Jynneos vaccine is highly effective in preventing Mpox virus infection after receipt of 2 Jynneos doses. In fact the estimated incidence rate to have occurred is less than 0.8% in fully vaccinated persons.

In the period from May 2022 – May 2024, 271 mpox cases in fully vaccinated persons were reported to CDC from 27 US jurisdictions. The CDC data shows that among 32,819 probable or confirmed mpox cases during this time period, a total of 24,507 (75%) occurred in unvaccinated persons.1

“Of these 271 cases, 51 (19%) occurred during 2024. Vaccination status was missing for 3737 (11%) cases; an additional 4304 (13%) cases were excluded from analysis because the patient had received only 1 Jynneos vaccine dose or had received the second dose <14 days before illness onset, or because other exclusion criteria were met.1

They pointed out that compared with unvaccinated cases, a higher proportion of fully vaccinated cases occurred among non-Hispanic White individuals (59%) and people aged 30–39 years (47%).1

What You Need to Know

The Jynneos vaccine is reported to be 99% effective in preventing mpox virus infection after receiving two doses.

Between May 2022 and May 2024, there were 271 mpox cases among fully vaccinated individuals out of 32,819 probable or confirmed cases.

In the spring of 2023, Chicago experienced an mpox outbreak with a notable number of cases among fully vaccinated individuals. Of the 49 cases identified, 57% were in fully vaccinated persons.

Chicago Mpox Cluster
In the spring of 2023, the city of Chicago had an Mpox cluster amongst fully vaccinated (FV) individuals. During this outbreak, from March 18-June 27, 2023, investigators identified 49 mpox cases with 57% of these cases coming from fully vaccinated individuals.2

“Our investigation indicated that cases were likely due to frequent behaviors associated with mpox transmission, even with relatively high vaccine effectiveness and vaccine coverage. Cases after vaccination might occur in similar populations,” the investigators concluded.2

Last month, Bavarian Nordic announced the Jynneos vaccine was available for commercial purchase in the US. Health care providers can order the vaccine through wholesalers and distribution partners, making it accessible at pharmacies, physician offices, and public health clinics.3

1. Guagliardo SA, Kracalik I, Carter RJ, et al. Monkeypox Virus Infections After 2 Preexposure Doses of JYNNEOS Vaccine — United States, May 2022–May 2024. MMWR Morb Mortal Wkly Rep 2024;73:460–466. DOI:
2. Faherty EAG, Holly T, Ogale YP, et al. Investigation of an mpox outbreak affecting many vaccinated persons in Chicago, IL–March 2023–June 2023. Clin Infect Dis 2024;ciae181. PMID:38567460
3. Abene S. FDA-Approved Mpox Vaccine Now Commercially Available in the US. Contagion. April 2, 2024. May 23, 2024.

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