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.

Pregnancy: JYNNEOS® (MVA-BN, non-replicating live vaccinia) has limited data in pregnant women. Animal studies showed no evidence of teratogenicity. During the 2022 mpox outbreak, the CDC recommended offering JYNNEOS® to pregnant persons with known mpox exposure, as mpox during pregnancy is associated with miscarriage, stillbirth, preterm delivery, and congenital mpox. The non-replicating nature of MVA-BN reduces theoretical risk compared to replication-competent smallpox vaccines. Individual risk–benefit assessment is recommended.

Breastfeeding: JYNNEOS® (MVA-BN, non-replicating live vaccinia) has limited data in lactating women. As a non-replicating vaccine, the risk of vaccine virus transmission through breast milk is theoretically lower than with replication-competent smallpox vaccines. During mpox outbreaks, vaccination may be considered for breastfeeding women with exposure, weighing the risk of mpox disease against the uncertain risk to the infant. Consult with a healthcare provider for individual risk assessment.

Pediatric use: JYNNEOS® is approved for adults ≥18 years in the US, though it has been used off-label in children during mpox outbreaks under emergency use authorization. In pediatric use during outbreaks, dosing follows adult dosing (0.5 mL subcutaneous, 2 doses 28 days apart). Children may be at risk of mpox through household contact with infected persons. ACAM2000® (replication-competent smallpox vaccine) has significant pediatric risks including progressive vaccinia and myocarditis and should only be used in children during emergencies.

Older adults (≥65 years): JYNNEOS® can be administered to older adults at risk of mpox exposure. Adults who received childhood smallpox vaccination (routine vaccination ended in the 1970s–1980s) may have residual cross-protective immunity against mpox, though this wanes over decades. JYNNEOS® is recommended regardless of prior smallpox vaccination for individuals at current risk. Older adults may experience more pronounced local and systemic reactions. No dose adjustment is required.

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.