Jynneos

Pronunciation: Jin-nee-os
Generic name: smallpox and Mpox vaccine, live, non-replicating
Dosage form: injectable suspension for subcutaneous use
Drug class: Viral vaccines

Medically reviewed by Carmen Pope, BPharm. Last updated on Apr 30, 2025.

What is Jynneos?

Jynneos is used to help prevent smallpox and Mpox (monkeypox) disease in adults 18 years and older who have been determined to be at high risk for smallpox or Mpox infection. Jynneos is given subcutaneously as 2 doses, 4 weeks apart.

Like any vaccine, Jynneos may not protect against disease in every person.

There are 2 formulations of Jynneos vaccine - a liquid-frozen formulation (approved by the FDA in September 2019) and a freeze-dried formulation (approved on March 28, 2025).

• The liquid-frozen, one-vial formulation has specific cold chain requirements and must be kept frozen at -25°C to -15°C (-13°F to +5°F).
• The freeze-dried, two-vial formulation only requires refrigeration at +2°C to +8°C (+36°F to +46°F) and offers advantages in terms of transportation, storage conditions, and shelf life.
• Having both formulations available is important for long-term stockpiling.

Jynneos also has an Emergency Use Authorization (EUA) to prevent Mpox disease in people younger than 18 years of age who are determined to be at high risk of Mpox infection.

Side effects

The most common side effects of Jynneos in those who have never received the vaccine before are:

• pain, redness, swelling, induration (hardening or thickening of tissue), and itching at the injection site
• muscle pain
• headache
• fatigue/tiredness
• nausea
• chills.

The most common side effects of Jynneos in those who have received the vaccine before are:

• redness, pain, induration, swelling, and itching at the injection site
• fatigue
• headache
• muscle pain.

This is not a complete list of side effects, and others may occur. Call your doctor for medical advice about side effects. You may report vaccine side effects to Bavarian Nordic at toll-free phone 1-833-365-9596 or VAERS at 1-800-822-7967 or www.vaers.hhs.gov.

Related/similar drugs

Warnings

Use Jynneos only as directed. Tell your doctor if you use other medicines or have other medical conditions or allergies.

Jynneos can cause a severe allergic reaction. Medical treatment must be available to treat any anaphylactic reactions following administration. Get emergency medical help if you have signs of an allergic reaction to Jynneos: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

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

Vaccination with Jynneos may not protect all patients.

Before taking this medicine

You should not receive Jynneos if you have ever had a life-threatening allergic reaction to a smallpox or Mpox vaccine.

Tell your doctor if you have a weak immune system caused by receiving certain medicines such as steroids, chemotherapy, or radiation.

Tell your doctor if you are pregnant or breastfeeding.

How is Jynneos given?

Jynneos is injected under the skin (subcutaneous injection), preferably into the upper arm. You will receive this vaccine in a doctor's office, clinic, or pharmacy.

Jynneos is administered in 2 doses, 4 weeks apart.

• You must have both vaccinations.
• Talk with your doctor if you had a severe reaction after the first dose.

Jynneos is also authorized by the FDA for emergency use as a smaller dose for administration between the layers of skin (intradermal injection) to increase available vaccine doses to meet increased demand during a public health emergency.

Your doctor or pharmacist can provide more information about this vaccine. Additional information is available from your local health department or the Centers for Disease Control and Prevention.

Dosing information

Usual Adult Dose for Prevention of Smallpox and Mpox:

Standard Regimen: Two subcutaneous doses of 0.5 mL each, 4 weeks apart.

Alternative Regimen (Emergency Use Authorization): Two intradermal doses of 0.1 mL each, 4 weeks apart (used to increase supply of vaccine doses during a public health emergency).

Usual Pediatric/Adolescent Dose for Prevention of Mpox (EUA):

Standard Regimen: Two subcutaneous doses of 0.5 mL each, 4 weeks apart. 

What happens if I miss a dose?

Be sure you receive all recommended doses of Jynneos. You may not be fully protected against disease if you do not receive the full series.

What happens if I overdose?

Since this vaccine is given by a healthcare professional, an overdose is unlikely to occur.

What should I avoid while receiving Jynneos?

Follow your doctor's instructions about any restrictions on food, beverages, or activity.

What other drugs will affect Jynneos?

Before receiving Jynneos, tell the doctor about all other vaccines you have recently received.

Also, tell the doctor if you have recently received drugs or treatments that can weaken the immune system, including:

• an oral, nasal, inhaled, or injectable steroid medicine;

• medications to treat psoriasis, rheumatoid arthritis, or other autoimmune disorders; or

• medicines to treat or prevent organ transplant rejection.

This list is not complete. Other drugs may interact with Jynneos, including prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible interactions are listed in this medication guide.

Ingredients

Jynneos is supplied in two presentations.

One-Vial Presentation:
The one-vial presentation contains Jynneos in a single vial with a yellow cap and does not require reconstitution before use.

Two-Vial Presentation:
The two-vial presentation includes a vial with a yellow cap containing Lyophilized Antigen Component and a vial with a blue cap containing Diluent Component. The Lyophilized Antigen Component must be reconstituted with the Diluent Component to form JYNNEOS prior to administration.

Each 0.5 mL dose contains:

• Modified Vaccinia Ankara-Bavarian Nordic (MVA-BN) live virus: 0.5 × 10⁸ to 3.95 × 10⁸ infectious units
• Tris (tromethamine): 0.61 mg
• Sodium chloride: 4.09 mg

After reconstitution with Water for Injection, it also contains:

• Dextran 40: 9.45 mg
• Sucrose: 22.5 mg
• Potassium L-glutamate monohydrate: 0.054 mg

May contain trace amounts of:

• Host-cell DNA: ≤20 mcg
• Protein: ≤500 mcg
• Benzonase: ≤0.0025 mcg
• Gentamicin: ≤0.400 mcg
• Ciprofloxacin: ≤0.005 mcg.

Administer two doses (0.5 mL each) 4 weeks apart.

Storage

Jynneos one vial presentation:

• Keep frozen at -25°C to -15°C (-13°F to +5°F).
• Store it in the original package to protect it from light.
• Do not re-freeze a vial once it has been thawed.
• Once thawed, the vaccine may be kept at +2°C to +8°C (+36°F to +46°F) for 4 weeks.
• Do not use the vaccine after the expiration date. 

Jynneos two-vial presentation:

• Lyophilized Antigen Component:
  • Store refrigerated at +2°C to +8°C (+36°F to +46°F).
  • Store in the original package to protect the vial from light.
  • Do not use the vaccine after the expiration date shown on the vial label.
• Diluent Component:
  • Store at room temperature (+20°C to +25°C, +68°F to +77°F) or refrigerated (+2°C to +8°C, +36°F to +46°F).

Storage After Reconstitution

• After reconstitution, use immediately or store refrigerated at +2°C to +8°C (+36°F to +46°F), away
  from light, for up to 12 hours. Do not freeze the reconstituted vaccine. 

Manufacturer

Jynneos (smallpox and Mpox vaccine) is manufactured by Bavarian Nordic A/S, with headquarters in Hellerup, Denmark.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Medical Disclaimer