Recommended Vaccine for Monkeypox
JYNNEOS (Modified Vaccinia Ankara vaccine) is the recommended vaccine for monkeypox prevention in the United States, administered as a 2-dose series given 28 days apart. 1, 2
Vaccine Specifications
JYNNEOS is a live, nonreplicating viral vaccine that offers critical safety advantages over older smallpox vaccines. 2, 3 The standard dosing regimen consists of:
- 0.5 mL subcutaneous injection for the licensed 2-dose series 2
- 0.1 mL intradermal injection available under FDA Emergency Use Authorization for adults ≥18 years to expand vaccine supply 2, 4
- 28-day interval between doses for optimal protection 2, 4
Primary Indications
Post-Exposure Prophylaxis (Highest Priority)
Vaccinate within 3-4 days of exposure for maximum benefit in preventing or decreasing disease severity. 1, 5 This includes persons with:
- Face-to-face, household, or close-proximity contact (within 6.5 feet) with confirmed or suspected mpox patients 1, 5
- Contact occurring from fever onset in the index case until all scabs have separated 1, 5
- Healthcare personnel involved in direct medical care, evaluation, or transportation of mpox patients 1
Pre-Exposure Prophylaxis (Occupational)
Routine vaccination is indicated for: 1
- Laboratory workers directly handling cultures or animals contaminated with monkeypox virus or other non-highly attenuated orthopoxviruses 1, 6
- Personnel working with vaccinia virus, recombinant vaccinia viruses, or cowpox 1, 6
- Revaccination every 10 years, though every 3 years can be considered for enhanced protection 1, 6
Special Populations
Pregnant Women
Vaccinate pregnant women with definite mpox exposure, as the risks of clinical mpox infection substantially outweigh potential vaccination risks. 5 This represents a critical departure from older vaccinia vaccines that were contraindicated in pregnancy. 6
Children
Vaccinate children of any age with definite exposure risk. 5 The 0.5 mL subcutaneous dose is authorized for persons <18 years under the EUA. 2
Immunocompromised Patients
Still vaccinate immunocompromised individuals, though effectiveness may be reduced. 5 JYNNEOS is nonreplicating, making it safer than ACAM2000 (the replicating smallpox vaccine) which should never be used in immunocompromised persons or their household contacts. 6, 3
Vaccine Effectiveness
Real-world data demonstrates substantial protection:
- 14.3-fold reduction in monkeypox incidence among persons receiving ≥1 dose compared to unvaccinated persons 7
- Protection evident ≥14 days after a single dose 7
- Strong orthopoxvirus-specific antibody response peaks around day 42 (2 weeks after second dose) 8
- Neutralizing antibodies generated against both vaccinia virus and monkeypox virus 8
However, complete 2-dose series is necessary for optimal protection. 7, 4 Among eligible recipients, only 57.6% completed the second dose during the 2022 outbreak, representing a critical gap in protection. 4
Safety Profile
Postlicensure surveillance confirms excellent safety: 2
- Most common adverse events are nonserious injection site reactions 2
- Similar adverse event rates for intradermal versus subcutaneous administration 2
- Serious adverse events are rare in adults 2
- No serious adverse events identified in persons <18 years 2
This contrasts sharply with ACAM2000 (the replicating vaccinia vaccine), which carries risks of cardiac complications, inadvertent inoculation, and transmission to immunocompromised contacts. 6, 3
Critical Vaccine Timing Considerations
Do not administer JYNNEOS simultaneously with varicella vaccine—maintain >4 weeks separation to avoid confusion in identifying which vaccine caused any postvaccination skin lesions. 1, 6
JYNNEOS can be administered simultaneously with any inactivated vaccine (e.g., influenza). 6
Common Pitfalls to Avoid
- Delaying second dose beyond 28 days: While protection begins after one dose, the complete series is essential for optimal immunity 7, 4
- Confusing JYNNEOS with ACAM2000: ACAM2000 is a replicating vaccine with significant contraindications and should not be used in household contacts of immunocompromised patients 6
- Withholding vaccine from special populations: Unlike older vaccines, JYNNEOS has no absolute contraindications when exposure risk is high 5