Mpox Vaccine

Adults ≥18 years at risk of mpox exposure: persons with multiple sexual partners in areas with mpox outbreaks, men who have sex with men (MSM) at high risk, healthcare workers caring for mpox patients, laboratory personnel handling orthopoxvirus specimens. Post-exposure prophylaxis (PEP): within 4 days of exposure (ideally) to prevent disease, or within 14 days to reduce severity. Travelers to regions with active Clade I or Clade II outbreaks.

Severe allergic reaction (anaphylaxis) to a previous dose or any component (including gentamicin, ciprofloxacin, chicken protein). Moderate to severe acute illness (defer). Note: unlike traditional smallpox vaccines (ACAM2000), Jynneos is NOT contraindicated in immunocompromised individuals, persons with atopic dermatitis/eczema, or pregnant women (when benefit outweighs risk).

Very common (≥1/10): injection site pain (85%), redness (61%), swelling (52%), induration (46%), itching (44%), fatigue (30%), headache (18%), myalgia (20%), nausea (10%). Common: chills, fever. Injection site reactions more pronounced after dose 2. Cardiac events: no signal of myocarditis/pericarditis (unlike replicating vaccinia — ACAM2000). Serious adverse events: rare (<0.1%).

Standard (subcutaneous): 2 doses of 0.5 mL SC, 28 days apart. Dose-sparing (intradermal): 2 doses of 0.1 mL ID, 28 days apart (EUA authorization). Post-exposure: 2 doses, first dose within 4 days of exposure. Previously vaccinated with smallpox vaccine: single booster dose. Store frozen at -20°C (long-term) or +2°C to +8°C (up to 8 weeks).

Pre-exposure: 80% effectiveness against mpox infection in observational studies during 2022 Clade IIb outbreak. Two doses confer significantly better protection than single dose (36% vs 66–86%). Post-exposure (within 4 days): approximately 78–86% effectiveness against confirmed mpox. Immunogenicity: ≥95% seroconversion by PRNT after 2 doses.

Can be co-administered with inactivated vaccines at different injection sites. Limited data on co-administration with live vaccines — standard spacing of same day or ≥4 weeks applies. No known drug interactions. Immunosuppressive therapy does not contraindicate vaccination (MVA-BN is non-replicating) but may reduce immunogenicity.

Safe in immunocompromised individuals including HIV-positive persons (major advantage over ACAM2000). Safe in persons with atopic dermatitis/eczema. Pregnancy: limited data, use when benefit outweighs risk (no teratogenicity in animal studies). Breastfeeding: insufficient data, consider risk-benefit. Intradermal administration (dose-sparing): authorized for ≥18 years under EUA, requires trained personnel.