Effectiveness of JYNNEOS Vaccine Against Diagnosed Mpox Infection

New York, 2022

Eli S. Rosenberg, PhD; Vajeera Dorabawila, PhD; Rachel Hart-Malloy, PhD; Bridget J. Anderson, PhD; Wilson Miranda, MPH; Travis O'Donnell; Charles J. Gonzalez, MD; Meaghan Abrego, MPH; Charlotte DelBarba, MPH; Cori J. Tice, MPH; Claire McGarry, MPH; Ethan C. Mitchell, MPH; Michele Boulais, MPA; Bryon Backenson, MS; Michael Kharfen; James McDonald, MD; Ursula E. Bauer, PhD


Morbidity and Mortality Weekly Report. 2023;72(20):559-563. 

In This Article

Abstract and Introduction


In 2022, an international Monkeypox virus outbreak, characterized by transmission primarily through sexual contact among gay, bisexual, and other men who have sex with men (MSM), resulted in 375 monkeypox (mpox) cases in the state of New York outside of New York City (NYC).*,† The JYNNEOS vaccine (Modified Vaccinia Ankara vaccine, Bavarian Nordic), licensed by the U.S. Food and Drug Administration (FDA) against mpox as a 2-dose series, with doses administered 4 weeks apart,§ was deployed in a national vaccination campaign. Before this outbreak, evidence to support vaccine effectiveness (VE) against mpox was based on human immunologic and animal challenge studies.[1–3] New York State Department of Health (NYSDOH) conducted a case-control study to estimate JYNNEOS VE against diagnosed mpox in New York residents outside of NYC, using data from systematic surveillance reporting. A case-patient was defined as a man aged ≥18 years who received a diagnosis of mpox during July 24–October 31, 2022. Contemporaneous control patients were men aged ≥18 years with diagnosed rectal gonorrhea or primary syphilis and a history of male-to-male sexual contact, without mpox. Case-patients and control patients were matched to records in state immunization systems. JYNNEOS VE was estimated as 1 – odds ratio (OR) x 100, and JYNNEOS vaccination status (vaccinated versus unvaccinated) at the time of diagnosis was compared, using conditional logistic regression models that adjusted for week of diagnosis, region, patient age, and patient race and ethnicity. Among 252 eligible mpox case-patients and 255 control patients, the adjusted VE of 1 dose (received ≥14 days earlier) or 2 doses combined was 75.7% (95% CI = 48.5%–88.5%); the VE for 1 dose was 68.1% (95% CI = 24.9%–86.5%) and for 2 doses was 88.5% (95% CI = 44.1%–97.6%). These findings support recommended 2-dose JYNNEOS vaccination consistent with CDC and NYSDOH guidance.

The first mpox case in New York outside NYC was reported on June 2, 2022. On June 28, the U.S. Department of Health and Human Services' Administration for Strategic Preparedness and Response announced a phased, jurisdictional rollout of the JYNNEOS vaccine from the Strategic National Stockpile, prioritizing postexposure prophylaxis (PEP) and vaccination of persons with recent or ongoing risks for mpox infection.** The first New York allocation of 2,206 vials was received July 6. By September 12, a total of 35,666 vials had been delivered.†† NYSDOH coordinated vaccine distribution in New York outside NYC with local health departments and community organizations.

All mpox, gonorrhea, and syphilis diagnoses in New York outside of NYC are reportable to NYSDOH.§§ Reports are investigated by public health staff members and entered into the Communicable Disease Electronic Surveillance System (CDESS). Case-patients were males at birth aged ≥18 years with a diagnosis of laboratory-confirmed mpox from whom specimens were collected during July 24–October 31, 2022 (2 weeks after vaccine campaign launch through the end of mandatory dose reporting to the New York State Immunization Information System [NYSIIS]). Control patients were males at birth aged ≥18 years with rectal gonorrhea or primary syphilis diagnosed within the same time frame as the mpox cases, and with presumptive sexual contact with a male or transgender person.¶¶

Demographic characteristics of case- and control patients were compared using Wilcoxon rank-sum and Pearson's chi-square tests. Case- and control patient records in CDESS were matched to NYSIIS*** by name and date of birth to ascertain JYNNEOS vaccination status and history, an approach similar to that used in a COVID-19 VE study.[4] Vaccination status was categorized into four groups, including one unvaccinated group (no JYNNEOS doses received) or one of three vaccinated groups: 1) with mpox or sexually transmitted infection (STI) specimen collected <14 days after receipt of dose 1; 2) ≥14 days after dose 1; or 3) after dose 2.[5,6] To estimate adjusted VE, conditional logistic regression models of case- and control patient vaccination status and dose history were used, matched on diagnosis week, with covariates including age, race and ethnicity, and region within New York outside NYC. VE values (with 95% CIs) were estimated as 1 – OR x 100, comparing each vaccinated category with the unvaccinated group.††† Four sensitivity analyses were conducted to examine uncertainties in case- and control patient definitions. All 1-dose VE estimates were reported for doses received ≥14 days earlier, unless otherwise specified. Statistical analyses were carried out using SAS software (version 9.4; SAS Institute). This analysis was determined to be nonresearch by the NYSDOH Institutional Review Board.

During June 2–December 31, 2022, a total of 375 mpox cases were reported to NYSDOH and the administration of 27,385 JYNNEOS doses was recorded in NYSIIS, including 16,769 (61%) first doses and 10,616 (39%) second doses (Figure). The reported number of cases peaked in mid-August, 5 weeks after launch of the JYNNEOS vaccination campaign. During July 24–October 31, a total of 252 male mpox case-patients and 255 STI control patients (175 with rectal gonorrhea and 80 with primary syphilis) met inclusion criteria. The age distribution was similar for case-patients (median = 32.1 years; range = 18.5–66.4 years) and control patients (median = 31.3 years; range = 19.4–74.3 years) (p = 0.47). Among persons with known ethnicity, Hispanic ethnicity was more prevalent among case-patients (43.6%) than among controls (18.9%; p<0.001) (Table 1). In addition, 68.7% of case-patients lived in the metropolitan region outside NYC, compared with 35.7% of control patients (p<0.001).


Reported mpox cases and first and second JYNNEOS vaccine doses administered, by week — New York,* June 2–December 31, 2022
Abbreviation: Mpox = monkeypox.
*Outside of New York City.

Among the 252 mpox case-patients, 22 (8.7%) had received the JYNNEOS vaccine, including 10 (4.0%) who had received 1 dose <14 days earlier, 10 (4.0%) who had received 1 dose ≥14 days earlier, and two (0.8%) who had received 2 doses; 230 (91.3%) were not vaccinated (Table 2). Among 255 control patients, 51 (20%) had received the JYNNEOS vaccine, including 42 (16.5%) who received an STI diagnosis ≥14 days after receiving 1 dose (23; 9.0%) or 2 doses (19; 7.5%). This corresponded to adjusted VE for combined 1 dose or 2 doses of 75.7% (95% CI = 48.5%–88.5%); 1-dose VE was 68.1% (95% CI = 24.9%–86.5%) and 2-dose VE was 88.5% (95% CI = 44.1%–97.6%). No significant VE was observed within 13 days of receipt of dose 1.

The first of the four sensitivity analyses (Supplementary Table, https://stacks.cdc.gov/view/cdc/128142) excluded men aged ≥50 years, who might have received a smallpox vaccine before routine nonmilitary U.S. vaccination ended in 1972; this analysis detected nearly identical VE as the main sensitivity analysis. The second sensitivity analysis included 71 secondary syphilis diagnoses in the control group, resulting in 1-dose or 2-dose combined VE of 64.8% (95% CI = 26.7%–83.1%). Among control patients, 213 (83.5%) had known reasons for testing: 88 (41.3%) because of symptoms, 19 (8.9%) because of partner referral, 103 (48.4%) for screening, and three (1.4%) for another reason. The third analysis restricted control patients to those persons testing for symptoms or referrals; 1-dose or 2-dose VE was 63.6% (95% CI = 8.0%–85.6%).§§§ The final sensitivity analysis limited observations to persons with known race and ethnicity and estimates increased modestly from the primary analysis, with 1-dose or 2-dose VE of 80.5% (95% CI = 56.1%–91.3%).

§The JYNNEOS vaccine is FDA-licensed for 0.5 mL doses, administered subcutaneously. Beginning August 9, 2022, FDA authorized 0.1 mL intradermal administration as a dose-sparing strategy, based on available evidence. NYSDOH implemented intradermal administration on August 29, 2022, after a brief transition period.
†† https://aspr.hhs.gov/SNS/Pages/JYNNEOS-Distribution.aspx
§§ https://regs.health.ny.gov/content/section-210-reporting-cases-or-suspected-cases-or-outbreaks-communicable-disease-physicians
¶¶Persons reported as male mpox case-patients were presumed to be MSM in this analysis (among 70% of patients with recorded sexual activity within 21 days, 85% reported male or transgender partners). All rectal gonorrhea diagnoses were included (among 63% of patients with partner data, 98% reported male or transgender partners). For primary syphilis, diagnoses were excluded if the person reported no male-to-male sexual contact (84% reported risk factor data).
***Doses of JYNNEOS vaccine administered in New York outside of NYC are reportable to NYSIIS. Doses given to persons in NYC are reported to the Citywide Immunization Registry, which sends all non-NYC New York residents' records to NYSIIS.
†††Two separate models considered the main four-level dose classification and one that combined "≥14 days after dose 1" and "dose 2" into a single level.
§§§STIs detected via asymptomatic screening might have been acquired several weeks or months previously, whereas symptomatic STIs are likely more recently acquired. Thus, persons with STIs detected via asymptomatic screening might be at lower current risk for mpox than are persons with symptomatic STIs. Also, persons with health-seeking behaviors (such as STI screening) might be more likely to receive the JYNNEOS vaccine. Alternatively, because asymptomatic screening is recommended annually for all sexually active MSM and every 3–6 months for those with increased behavioral risk, sampling routinely screening MSM might select for those at elevated risk for mpox. https://www.cdc.gov/std/treatment-guidelines/default.htm