What is Journavax?

JYNNEOS Vaccine: A Comprehensive Overview

JYNNEOS is an FDA-approved vaccine for the prevention of monkeypox (mpox) and smallpox infections, with demonstrated effectiveness in reducing infection risk and disease severity during the 2022-2024 mpox outbreak in the United States.

Vaccine Characteristics and Administration

• JYNNEOS (Modified Vaccinia Ankara vaccine, manufactured by Bavarian Nordic) is a live, nonreplicating viral vaccine licensed for prevention of smallpox and mpox in adults aged ≥18 years 1.
• The standard FDA-approved regimen is a 0.5-mL 2-dose series administered subcutaneously 28 days apart 1.
• During the 2022 mpox outbreak, an Emergency Use Authorization (EUA) was issued on August 9,2022, allowing:
  • Intradermal administration of 0.1-mL doses for adults ≥18 years (dose-sparing strategy) 2.
  • Subcutaneous administration of 0.5-mL doses for persons <18 years 1.

Effectiveness

• JYNNEOS vaccine demonstrates significant protection against mpox infection:
  • A multijurisdictional case-control study showed adjusted vaccine effectiveness of 75.2% for partial vaccination (1 dose) and 85.9% for full vaccination (2 doses) 2.
  • Another nationwide study using electronic health record data found vaccine effectiveness of 35.8% after one dose and 66.0% after two doses 3.
• Effectiveness by administration route:
  • Subcutaneous: 88.9% effectiveness with full vaccination 2.
  • Intradermal: 80.3% effectiveness with full vaccination 2.
  • Heterologous (mixed subcutaneous and intradermal): 86.9% effectiveness with full vaccination 2.
• The vaccine remains effective in immunocompromised individuals, though with slightly reduced efficacy (70.2% vs. 87.8% in immunocompetent individuals) 2.

Safety Profile

• The most common adverse events are nonserious and include injection site reactions, consistent with prelicensure studies 1.
• Adverse events occur at similar rates for both intradermal and subcutaneous administration 1.
• Serious adverse events are rare in adults, and no serious adverse events have been identified in persons under 18 years of age 1.
• Postlicensure and postauthorization surveillance data support the overall safety profile of JYNNEOS 1.

Breakthrough Infections

• While effective, breakthrough infections can occur in fully vaccinated individuals:
  • From May 2022 to May 2024,271 mpox cases among fully vaccinated persons were reported from 27 U.S. jurisdictions, estimated to be <1% of fully vaccinated persons 4.
  • Breakthrough infections tend to be less severe than infections in unvaccinated individuals 4.
  • Breakthrough infections were more commonly reported after heterologous vaccination (46%) or homologous subcutaneous vaccination (32%) than after homologous intradermal vaccination (22%) 4.
• The median interval between second vaccine dose and illness onset was longer for intradermal recipients (363 days) compared to subcutaneous recipients (263 days), suggesting no evidence of waning immunity 4.

Vaccination Strategy and Implementation

• During the 2022 mpox outbreak, the U.S. vaccination strategy focused primarily on:
  • Persons with known or presumed exposures to monkeypox (postexposure prophylaxis) 5.
  • Persons at high risk for exposure or occupational exposure (preexposure prophylaxis) 5.
• By October 10,2022,931,155 doses of JYNNEOS had been administered and reported to CDC 5.
• Initial vaccine supplies were constrained, leading some jurisdictions to prioritize first dose administration during May-July 2022 5.
• The August 2022 EUA for intradermal administration substantially expanded available vaccine supply 5.

Recommendations

• The Advisory Committee on Immunization Practices (ACIP) recommends the complete 2-dose series for optimal protection, regardless of administration route or immunocompromise status 2.
• At this time, additional doses beyond the 2-dose series are not recommended, even for those at continued risk 4.
• Complete vaccination series is important, as only 57.6% of those who received a first dose completed their second dose during the initial vaccination campaign 5.

Special Considerations

• Demographic disparities in vaccination were observed initially but improved over time:
  • Early in the campaign (May-June 2022), only 5.6% of vaccine recipients were Black and 15.5% were Hispanic 5.
  • By July-October 2022, these percentages increased to 13.3% and 22.7%, respectively 5.
• Equitable access to vaccination should be an essential factor in planning vaccination programs and strategies 5.