The mpox vaccine helps protect against mpox, a viral infection caused by the Orthopoxvirus genus. The main vaccine used in the United States is called JYNNEOS, and it can be used to prevent both smallpox and mpox. Another older vaccine, ACAM2000, can also provide protection but has a higher risk of side effects.
JYNNEOS has been shown to produce strong immune responses, generating neutralizing antibodies that protect against mpox infection. Real-world studies confirm that one or two doses can significantly reduce the risk of infection and the severity of the disease.
The Centers for Disease Control and Prevention (CDC) recommends the mpox vaccine for people who are more likely to be exposed to the virus, such as healthcare workers or those who have had recent contact with someone infected. Vaccination can be given before or after exposure and helps prevent serious complications and hospitalization.
When it is indicated
The mpox vaccine is approved to prevent mpox and smallpox in adults aged 18 years and older who are at higher risk of exposure. This includes laboratory workers who handle Orthopoxviruses, healthcare professionals who care for mpox patients, and individuals with known or suspected exposure to an infected person.
It is also recommended for people with multiple sexual partners in areas with ongoing mpox transmission, as well as for those who have been in close contact with confirmed cases.
For post-exposure prevention, the vaccine should ideally be administered within 4 days of exposure to stop the infection from developing, or up to 14 days to help reduce symptoms if the disease occurs.
Recommended dose
The mpox vaccine, JYNNEOS, is given as a two-dose series, with each dose 28 days apart. Each dose contains 0.5 mL when injected subcutaneously or 0.1 mL when given intradermally under emergency authorization during vaccine shortages.
A person is considered fully vaccinated two weeks after receiving the second dose. For people who were previously vaccinated with an older smallpox vaccine, only one dose of JYNNEOS may be needed.
Booster doses are not routinely recommended for the general population but may be advised for certain occupational groups based on public health guidelines.
How it is administered
The mpox vaccine can be given either subcutaneously (under the skin) or intradermally (into the upper layer of the skin), depending on the available supply and the person’s age or health status. The intradermal method uses a smaller dose but offers a similar immune response, which allows more people to be vaccinated during outbreaks.
Subcutaneous injections are typically given in the upper arm, while intradermal injections are usually administered on the inner forearm. Both methods should only be performed by trained healthcare professionals using sterile techniques.
If the second dose is delayed, it should be given as soon as possible. There is no need to restart the vaccine series.
Possible side effects
Most side effects of the mpox vaccine are mild and short-lived. The most common include pain, redness, or swelling at the injection site, along with tiredness, headache, muscle pain, and mild fever.
Serious side effects are rare. Because JYNNEOS does not contain a live replicating virus, it cannot cause mpox or smallpox. Reports of myocarditis and pericarditis are very uncommon and usually mild.
In people with weakened immune systems or underlying health conditions, local reactions may be slightly more frequent but remain generally well tolerated.
Contraindications
The mpox vaccine should not be given to anyone with a known severe allergic reaction to any of its ingredients, including gentamicin, ciprofloxacin, or egg proteins used during manufacturing.
Vaccination should be postponed in people with moderate or severe acute illness until they recover. Those with skin conditions such as eczema or atopic dermatitis should be monitored closely, although JYNNEOS is generally safer for this group than older vaccines.
Pregnant or breastfeeding individuals can receive the vaccine if the potential benefits outweigh the risks, especially when they are at high risk of exposure.
Special populations
Research shows that the JYNNEOS mpox vaccine is safe and effective in adolescents and in people living with HIV, producing antibody responses similar to those seen in healthy adults.
For individuals with weakened immune systems, protection may be reduced, so other preventive measures should also be followed.