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Last reviewed
April 16, 2024

JYNNEOS® Mpox Smallpox Vaccine Clinical Trials, Dosage, News, Side Effects, Usage

Bavarian Nordic JYNNEOS® (MVA-BN®, IMVAMUNE®) two-dose vaccine is based on a live, attenuated vaccinia virus, Modified Vaccinia Ankara (MVA). The MVA is cultured in chicken embryo fibroblast cells and is a serum-free medium, incapable of replicating in the human body yet able to elicit a potent immune response. It is purified and filtered from the cells using various methods, including benzonase digestion. JYNNEOS was codeveloped with the U.S. Government (BARDA, BioShield) to ensure adult populations can be protected from smallpox, including people with weakened immune systems or at high risk of adverse reactions to traditional smallpox vaccines based on replicating vaccinia virus strains.

The U.S. Food and Drug Administration's (FDA ) initial approval of JYNNEOS for smallpox in 2019 was based on a comprehensive development program comprising 22 clinical trials, including two Phase 3 studies. The FDA approved JYNNEOS on September 24, 2019. The FDA granted Bavarian Nordic a Priority Review Voucher (PRV) under the Material Threat Medical Countermeasure program, accelerating the FDA's drug application review for mpox indication. The U.S. FDA's emergency use authorization (EUA) for JYNNEOS for mpox was issued by Peter Marks, MD, Ph.D., in Application Number 28801 on August 9, 2022. The FDA announced it issued an EUA (STN: 125678) enabling healthcare providers to administer JYNNEOS by intradermal injection for individuals at high risk for human monkeypox virus (hMPXV). On March 15, 2023, the U.S. FDA updated JYNNEOS - STN: BL 125678/20. Since the mpox Clade 2b virus outbreak began in May 2022. As of April 2024, JYNNEOS is the only FDA-approved non-replicating smallpox and mpox vaccine for military and non-military use and became commercially available at pharmacies in the U.S. in 2024.

In November 2021, the U.S. Centers for Disease Control and Prevention (CDC) vaccine committee unanimously voted for JYNNEOS as an alternative to the ACAM2000 vaccine for primary and booster doses against smallpox. The CDC's Advisory Committee on Immunization Practices (ACIP) group leader, Pablo Sanchez, MD, led the Mpox Vaccine presentation on October 20, 2022, and February 22, 2023. The CDC announced Interim Clinical Considerations on February 22, 2023: Mpox vaccination should continue to be offered to people with the highest potential for exposure to mpox. An updated U.S. National Mpox Vaccination Strategy was published on February 6, 2023. On June 23, 2023, Agam Rao, MD CAPT, U.S. Public Health Service, presented: Considerations for long-term protection against mpox - prefers no CDC recommendation for third JYNNEOS dose, including persons with advanced HIV or other severe immunocompromised immune systems. On August 18, 2023, the CDC's Morbidity and Mortality Weekly Report stated that all adults at risk for mpox should receive the JYNNEOS vaccine, regardless of childhood smallpox vaccination status.

On October 25, 2023, the CDC recommended using JYNNEOS routinely for people at risk of smallpox or mpox infection. Survey results published in the U.S. CDC's Emerging Infectious Diseases Volume 30, Number 5 May 2024, among vaccine-eligible GBMSM, uptake was 69% (95% CI 65%–72%; 601/875) and 92% (95% CI 89%–94%; 601/655) among those offered the JYNNEOS vaccine.

Dr. Zhilong Yang, an associate professor in the Texas A&M School of Veterinary Medicine & Biomedical Sciences Department of Veterinary Pathobiology, stated on April 12, 2024, “Smallpox vaccines and drugs also hold the promises and potentials to prevent and treat mpox and other viruses within the same family of smallpox virus, which is another important reason that we should continue to research poxviruses and develop smallpox medical countermeasures, including diagnostics, vaccines and therapeutics,”

Bavarian Nordic A/S, headquartered in Kvistgaard, Denmark (OTCMKTS: BVNRY) (OMX: BAVA), focuses on developing, manufacturing, and commercializing life-saving vaccines. The MVA-BN® vaccine is marketed under the brand names IMVANEX® in the European Union and IMVAMUNE® in Canada. On July 25, 2022, the European Commission extended Imvanex's marketing authority to include mpox. On August 3, 2023, Bavarian Nordic announced it would manufacture and supply additional liquid-frozen doses of JYNNEOS to the U.S. government in 2023, valued at $3 million. Additionally, on August 3, 2023, Bavarian Nordic A/S announced that BARDA placed a new order valued at $120 million, primarily manufacturing a new bulk product for the JYNNEOS smallpox/mpox vaccine.

JYNNEOS Vaccine Availability 2024

As of April 2024, healthcare providers in the U.S. can order JYNNEOS through their preferred wholesaler and distribution partners to make it available for at-risk individuals at pharmacies, physician offices, and public health clinics. Healthcare providers in the U.S. must administer JYNNEOS for free, regardless of any administration fee. As of April 3, 2024, Morris & Dickson became the first U.S. distributor of JYNNEOS. According to estimates from the CDC, two million U.S. individuals are eligible for mpox vaccination. Recent data shows that 15% of eligible people have received only one dose of the JYNNEOS vaccine. The CDC's Advisory Committee on Immunization Practices (ACIP) Adult Immunization Schedule includes JYNNEOS for 2023-2024.

As of 2023, about 1,257,943 doses had been administered in 57 U.S. Jurisdictions. As November 2023, JYNNEOS vaccinations been administered in cities such as American Samoa,   AnchorageAtlantaAustin, Baltimore, Birmingham,   BosieBoston, CaliforniaChicago, Connecticut,   Dallas,   Denver, GuamHouston, LaramieLittle RockLos AngelesMiami, New OrleansNew York City, OrlandoPheonixPhiladelphia, Pittsburg, PortlandSan AntonioSan Francisco, Washington DC, and Wilmington Del. In New York, NYCDOHMH receives the Jynneos vaccine directly from the federal government, distributing it within their jurisdiction. For more information on New York City, please visit this linkNew York City announced on September 13, 2022, that it would offer Jynneos vaccine second doses to people (3,402) who received their first dose on or before July 23, 2022. On October 3, 2022, the U.S. HHS published a Public Readiness and Emergency Preparedness Act declaration in the Federal Registry that grants pharmacists certain authorities to administer mpox vaccines. Since 2003, Bavarian Nordic has worked with the U.S. government on developing, manufacturing, and supplying a non-replicating smallpox vaccine. On August 29, 2022, HHS announced it would provide approximately $11 million to support the manufacturing of Jynneos in Grand Rapids, Michigan.

JYNNEOS Vaccine Efficacy

The Lancet Infectious Diseases reported on December 7, 2023, that 12% of vaccinated individuals were non-antibody responders, whereas all people with mpox infection developed a neutralizing antibody response. A case-series (67) study published by The Lancet Infectious Diseases on September 4, 2023, confirmed natural immunity and vaccine-induced immunity are not fully protective against mpox infection. Demographic subgroup information is available in Section 1.1 of the Clinical Review Memo for information about participation in the clinical trials and any notable analysis of demographic subgroup outcomes. And Section 6.2 (Postmarketing Experience) to the Package Insert.

A study published by The Lancet Infectious Disease on October 11, 2023, attempted to answer questions regarding the durability and strength of protection following infection and JYNNEOS vaccination. This analysis reported that people vaccinated with MVA-BN were found to develop frequently low or medium mpox neutralizing antibodies compared to infected individuals, as reported in 2023. Ten percent of vaccinated individuals showed no detectable neutralizing antibodies at six months, whereas every person with mpox infection developed antibodies.

On September 8, 2023, the U.S. CDC confirmed the JYNNEOS vaccine is not 100% effective. The CDC's ACIP reported in October 2023 JYNNEOS Vaccine Effectiveness (VE) against mpox ranges from 36%–75% for 1-dose vaccination and 66%–89% for 2-dose vaccination. VE trended higher for immunocompetent participants compared to self-reported immunocompromised participants. The Lancet Infectious Disease reported that the JYNNEOS vaccine showed an effectiveness of 66–78%, and second episodes of mpox and cases of breakthrough infections among fully vaccinated individuals have been reported. On June 29, 2023, Orginal Research estimated adjusted vaccine effectiveness was 66% (95% confidence interval [CI], 47.4 to 78.1), and 146 case patients and 1000 control patients received one dose, among whom the estimated adjusted vaccine effectiveness was 35.8% (95% CI, 22.1 to 47.1).

On May 18, 2023, the NEJM published data from Cosmos, a nationwide Epic EHR database, to assess the effectiveness of JYNNEOS vaccination in preventing mpox disease among adults who received two doses. The estimated adjusted vaccine effectiveness was 66% (95% confidence interval [CI], 47.4 to 78.1), and those who received one dose, among whom the estimated adjusted VE was 35.8% (95% CI, 22.1 to 47.1). The U.K. Health Security Agency (UKHSA) announced on November 22, 2022, its estimate of mpox vaccine effectiveness for one dose was 78% 14 or more days after vaccination. The journal Nature Medicine reported on January 31, 2023, that the real-world effectiveness of a single dose of JYNNEOS in males adjusted VE was estimated at 86% (95% confidence interval, 59–95%).

JYNNEOS's initial approval for mpox use is based on survival data from lethal mpox virus challenge studies (FDA's Animal Rule) in non-human primates. Overall survival in various models ranged from 80% to 100% of JYNNEOS-vaccinated animals, compared to 0-40% in control animals.

JYNNEOS Vaccine Efficacy Against Mpox Virus Clade I and Clade II

On March 14, 2024, the U.S. CDC's Agam Rao, MD CAPT, US Public Health Service, stated, 'JYNNEOS vaccination is expected to be effective regardless of mpox clade. Mpox virus Clade I is divided into lineages 1–5, while Clade II is divided into subclades IIa and IIb. Clade IIb is responsible for the global outbreak. On December 7, 2023, the CDC published a Health Alert Network Health Advisory stating that Mpox Vaccines are expected to be effective for both Clade I and Clade II MPXV infections. However, real-world data is lacking regarding Clade 1 effectiveness, as reported by the ECDC in December 2023.

JYNNEOS Breakthrough Mpox Infections

The U.S. CDC issued an MMWR on June 23, 2023, and the Clinician Outreach and Communication Activity (COCA) call on May 18, 2023, confirmed that a cluster of mpox cases was reported in Chicago, Illinois. During March 18–June 12, 2023, 40 laboratory-confirmed mpox cases were identified in Chicago, including 22 (55%), five (13%), and 13 (33%), respectively, among patients who had received two doses of JYNNEOS or one dose of ACAM2000 vaccine, those who had received one vaccine dose of JYNNEOS vaccine, and those who had not received any vaccines for mpox. The Colorado Department of Public Health and Environment reported on June 12, 2023, that three mpox cases were confirmed in Denver, and 2 cases involved people who were fully vaccinated with two doses of the Jynneos vaccine.


The European AIDS Clinical Society also recommends the vaccine for adults infected with HIV or on preexposure prophylaxis treatment, and it may support additional national recommendations for the vaccine in the future. On August 5, 2022, the early release of the CDC's Morbidity and Mortality Weekly Report - Interim Guidance - confirmed the JYNNEOS vaccine can be safely given to people who are living with HIV infection and those who are taking preexposure prophylaxis (PrEP).

JYNNEOS Vaccine Myocarditis Risk

According to the U.S. CDC, myocarditis and pericarditis have occurred following either primary vaccination or revaccination with live vaccinia virus smallpox vaccines and is a known health risk for military forces (2003). The CDC reported on October 25, 2023, that VAERS and VSD data suggest an increased risk for myocarditis or pericarditis following JYNNEOS. The possibility of a negligible risk, similar to smallpox vaccination, cannot be excluded.

JYNNEOS Vaccine Coadministration

As of April 2024, the CDC says there is limited clinical trial data on administering the JYNNEOS vaccine simultaneously with other vaccines.

JYNNEOS Vaccine Dosage

In the U.S., the standard U.S. FDA regimen for JYNNEOS involves subcutaneous administration with two injections of 0.5mL four weeks apart.

JYNNEOS Vaccine Booster

According to an abstract presented on March 30, 2024, 'it is premature to draw such conclusions. It is unclear how waning antibody levels relate to protection. Immunity also involves other elements, such as T-cell responses. Comprehensive clinical monitoring over time, which connects infection rates with antibody levels, is required to make informed decisions about (JYNNEOS) booster vaccination protocols.'

The U.S. CDC vaccine committee (ACIP) stated, 'Regarding booster doses, a systematic review identified one randomized controlled trial and 17 observational studies that included 6,417 subjects. After considering the geometric mean titer and seroconversion rate together, the Vaccine Work Group estimated with very low (level 4) certainty that a slight increase in disease prevention occurs after a third JYNNEOS dose versus the standard 2-dose primary series. However, the ACIP unanimously recommended JYNNEOS boosters as an alternative to ACAM2000 boosters in persons who received ACAM2000 vaccine as the primary vaccine.

JYNNEOS Pre and Post-Exposure Vaccination

A study published in January 2024 evaluated the potential to overestimate PEP effectiveness when using conventional analytic methods due to exposed individuals developing illness before they can obtain PEP compared to the target trial. These researchers concluded time to PEP in NYC, coupled with the observed incubation period, resulted in overestimated PEP effectiveness using a conventional method. The WHO's SAGE confirmed on October 10, 2022, that post-exposure vaccination (PEPV) is recommended for close contact with MPX cases, ideally within four days of first exposure and up to 14 days without symptoms.

JYNNEOS (MVA) Fractional Formulation Study

On December 14, 2023, the New England Journal of Medicine published a Correspondence that shows antibody levels against the mpox virus after JYNNEOS vaccination were similar regardless of whether the person received a smaller dose between layers of the skin rather than by the standard route under the skin. The NEJM published a Correspondence regarding a reanalysis of these trial results using the contemporaneous FDA Toxicity Grading Scale on April 14, 2023, that showed that the intradermal route was safe and did not lead to unacceptable local reactions. Although there was a higher incidence of moderate or severe erythema after the second vaccine dose than after the first dose, the median duration of erythema was shorter by one day in the intradermal-administration group than in the subcutaneous-administration group.


JYNNEOS (MVA-BN) Vaccine (IMVANEX, IMVAMUNE) utilizes Chicken Embryo Fibroblast cells to produce the vaccine.   Replication-competent poxvirus strains can cause clinical infection in humans and have an infectious virus that can be transmitted to others. However, replication-deficient poxvirus strains, including modified vaccinia Ankara (MVA), do not produce contagious viruses in humans and, therefore, do not cause clinU.Kl infection. As such, replication-deficient poxvirus strains pose a substantially lower risk of adverse events than replication-competent strains. 

JYNNEOS For Children

A peer-reviewed study funded by the U.K. Health Security Agency, published on June 15, 2023, concluded a single dose of MVA–B.N. for post-exposure prophylaxis was well-tolerated in children and induced robust antibody and cellular responses up to 15 weeks after vaccination. On September 15, 2022, the U.S. CDC confirmed that children and adolescents exposed to people with suspected or confirmed mpox infections might be eligible for post-exposure prophylaxis with vaccination. In addition, the CDC published interim Clinical guidance for Healthcare Providers in September 2022. However, the U.S. FDA says the safety and effectiveness of JYNNEOS have not been established in individuals under 18.

JYNNEOS For Pregnant Women

The U.S. FDA says available human data on JYNNEOS administered to pregnant women are insufficient to inform vaccine-associated risks in pregnancy. Four developmental toxicity studies conducted in female rats and rabbits evaluated the effect of JYNNEOS on embryo-fetal and post-natal development. As of October 27, 2022, the CDC confirmed no clinical efficacy data regarding pregnant or breastfeeding women.

JYNNEOS Side Effects

The risk of a severe allergic reaction should be weighed against the risk of disease due to smallpox or mpox. A Research Letter on May 5, 2023, reviewed a phase 4 clinical study of adverse events following Jynneos vaccination and found that local negative event rates were highest following intradermal administration. The adverse event rate was highest following dose 1 of intradermal vaccination (53%) and low immunization dose 2 of subcutaneous vaccination (31%). The adverse effects of immunization were local redness, itching, and swelling following intradermal vaccination and local pain, swelling, and redness following subcutaneous vaccination.

Jonathan Dufimmunization, Immunization Safety Office, CDC Advisory Committee on Immunization Practices, presented JYNNEOS Vaccine Safety Monitoring During the 2022 Mpox Outbreak on February 22, 2023. According to VAERS, the number of serious adverse events reported after JYNNEOS was 26. The CDC said on December 8, 2022, that the vaccine safety profile was consistent with prelicensure studies. The most common adverse health events reported were nonserious, including injection site reactions. Serious adverse events were rare among adults.

Severe adverse reactions known for replicating vaccinia virus strains, such as myocarditis, encephalitis, generalized vaccinia, or eczema vaccinatum, were not observed during Jynneos's clinical development program. The U.S. FDA reports in smallpox vaccine-naïve healthy adults, the most common (> 10%) solicited injection site reactions were pain (84.9%), redness (60.8%), swelling (51.6%), induration (45.4%), and itching (43.1%); the most common solicited systemic adverse reactions were muscle pain (42.8%), headache (34.8%), fatigue (30.4%), nausea (17.3%) and chills (10.4%).

JYNNEOS Contraindication 

According to the CDC, JYNNEOS is contraindicated in persons with serious allergies to any vaccine component.

JYNNEOS Immunocompromised

Immunocompromised persons, including those receiving immunosuppressive therapy, may have a diminished immune response to JYNNEOS.

JYNNEOS Storage Requirement

 JYNNEOS must be safely stored at negative 20 degrees Celsius (-20°C). 

MVA-BN® Global Availability

Bavarian Nordic A/S was awarded a contract on September 13, 2023, to supply its MVA-BN smallpox vaccine to rescEU, a strategic reserve within the European Union (E.U.). This new order follows an initial contract awarded in June 2023 and is also for delivery in 2024. rescEU was established as a reserve of European capacities, including medical items. As of 2023, the MVA-BN (Jynneos, IMVANEX, MVAMUNE) vaccine was available in Australia,   BrazilCanada, the CaribbeanCyprus, the Democratic Republic of CongoDenmarkEuropeFrance, Germany, Iceland, IndonesiaIsreal, ItalyMexicoNigeria, Norway, PortugalScotlandSpain, Taiwan, and the U.K. The U.K. NHS mpox outbreak vaccination program is now only available in London. The U.K. Health Security Agency is making second doses available. Mpox vaccination appointments are available using this NHS vaccine finder. As of August 7, 2023, a total of 77,809 mpox vaccination services have been completed in Taiwan, including 447 post-exposure prophylaxis vaccinations and 77,362 preexposure prophylaxis vaccinations. MVA-BN (IMVANEX®) was authorized by the European Medicines Agency (EMEA/H/C/002596) in 2013.

IMVAMUNE® Availability

IMVAMUNE® was authorized for use in the European Union under exceptional circumstances in July 2013. Since May 2022, the Canadian government has deployed over 145,000 vaccine doses of IMVAMUNE. Health Canada has approved the vaccine for use against mpox and smallpox.


Bavarian Nordic A/S received approvals from the U.S. and E.U. regulatory authorities on July 27, 2022, to manufacture JYNNEOS®/IMVANEX® smallpox and mpox vaccine at the Company's fill and finish facility in Denmark. In addition, on August 18, 2022, Bavarian Nordic announced that the Company had agreed with Grand River Aseptic Manufacturing to fill and finish 2.5 million JYNNEOS vaccines/vials.


The AMA-issued CPT code (90611) describes the FDA-approved JYNNEOS vaccine manufactured by BavariaU.S. to prevent smallpox and monkeypox disease in adults 18 years of age and older who are at high risk for smallpox or monkeypox infection.

JYNNEOS MVA-BN® Vaccine News 2023

April 2, 2024 - Brian Hujdich, Executive Director, National Coalition for LGBTQ Health, commented: “The expanded availability of JYNNEOS is a vital step toward ensuring equitable access to healthcare for the LGBTQ+ community and marks a significant stride in preventing the spread of mpox."

December 13, 2023 - Bavarian Nordic A/S announced that it had been awarded another contract valued at more than EUR 11 million to supply its MVA-BN® smallpox vaccine to rescEU, a strategic reserve within the E.U.

March 31, 2023 - U.S.The U.S. CDC reported that during the current multinational outbreak, U.S. 1- and 2-dose vaccination coverage among at-risk persons reached an estimated 37% and 23%, respectively.

JYNNEOS Vaccine Clinical Trial

A phase 2 study results posted as a preprint on September 9, 2022, concluded priming with either 1 or 2 doses of MVA-BN induced a durable immune memory, similar to that of older generation replicating smallpox vaccines. When the MVA-BN vaccine was administered as a booster to individuals either primed two years earlier with MVA-BN or an older generation replicating smallpox vaccine in the distant past, it elicited a similarly rapid and durable immune response that was generally safe and well-tolerated. One-dose priming with MVA induced a long-term B-cell memory that resulted in robust anamnestic responses following an MVA booster two years later, suggesting that a single dose may offer protection against future exposure.

The FDA approval of JYNNEOS for smallpox comes from a development program comprising 22 clinical trials, including two phase III trials. The program enrolled 7,871 individuals aged between 18 and 80 years who received at least one dose of the vaccine. Approval for monkeypox indication comes from survival data from studies conducted in non-human primates. The survival rate ranged from 80%-100% in animals vaccinated with JYNNEOS compared to 0%-40% in the control group.

Upon successful completion of the current study, expected in 2021, the Company plans to submit a supplement to the BLA to extend the approval for both formulations of MVA-BN, anticipated in 2022.

Clinical Trials

No clinical trials found