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Key Facts About Vaccines to Prevent Monkeypox Disease

Monkeypox is an orthopoxvirus that is related to the smallpox virus. It has been associated with sporadic outbreaks over the past decades. Since May 2022, an outbreak of monkeypox has been ongoing in several countries, including the United States.

People with monkeypox get a rash that may be painful or itchy and that may be located anywhere on the body. Some people also get flu-like symptoms. Monkeypox can spread until the rash has healed, all scabs have fallen off, and a fresh layer of skin has formed. The monkeypox virus can spread to anyone through close skin-to-skin contact. It can also spread through touching objects, fabrics, and surfaces that have been used by someone with monkeypox or by contact with respiratory secretions. The CDC provides additional information on how monkeypox can spread.


JYNNEOS is the only vaccine that is FDA-approved for the prevention of monkeypox disease. JYNNEOS is also approved for the prevention of smallpox disease. JYNNEOS is a live virus vaccine that contains Modified Vaccinia Ankara-Bavarian Nordic (MVA-BN), a weakened, non-replicating orthopoxvirus. JYNNEOS may be safely used in significantly immunocompromised individuals who may not be indicated or recommended to receive certain live vaccines.

JYNNEOS is approved for use in individuals 18 years of age and older who are determined to be at high risk for smallpox or monkeypox infection. JYNNEOS is approved for administration subcutaneously (beneath the skin), as a two-dose series, 4 weeks apart. JYNNEOS was originally developed for use in the event of a smallpox bioterrorist attack in certain populations (e.g., immunocompromised individuals) as an alternative to ACAM2000. ACAM2000 is an FDA-approved, live replicating vaccinia virus vaccine for the prevention of smallpox disease. It is associated with certain serious adverse reactions that have not been observed with JYNNEOS.

FDA Emergency Use Authorization of JYNNEOS Vaccine

On August 9, 2022, FDA issued an emergency use authorization (EUA) for JYNNEOS to allow healthcare providers to administer the vaccine intradermally (between the layers of the skin) for individuals 18 years of age and older who are determined to be at high risk for monkeypox infection. The EUA also allows for use of the vaccine in individuals younger than 18 years of age determined to be at high risk for monkeypox infection; in these individuals JYNNEOS is administered by subcutaneous injection. For all age groups, JYNNEOS is given as a two-dose series, 4 weeks apart.

In issuing this EUA, the FDA determined that the known and potential benefits of JYNNEOS outweigh the known and potential risks for the authorized uses.

A 2015 clinical study evaluated a two-dose series of JYNNEOS given intradermally compared to subcutaneously in individuals 18 years of age and older. Individuals who received the vaccine intradermally received a lower volume (one fifth) than individuals who received the vaccine subcutaneously. The results of this study demonstrated that intradermal administration produced a similar immune response to subcutaneous administration. Administration by the intradermal route resulted in more redness, firmness, itchiness and swelling at the injection site, but less pain.

To support the FDA’s authorization of two doses of JYNNEOS administered by the subcutaneous route of administration in individuals younger than 18 years of age, the FDA considered the available JYNNEOS safety and immune response data in adults as well as historical data with use of live vaccinia virus smallpox vaccine in pediatric populations. Additional information on FDA’s decision to authorize JYNNEOS for emergency use may be found here.

ACAM2000 Vaccine

ACAM2000 is not approved or authorized for emergency use against monkeypox. ACAM2000 may be used against monkeypox under FDA’s Expanded Access Investigational New Drug (IND) mechanism, which requires informed consent along with additional IND requirements.

ACAM2000, which is administered as a single dose, must be given by a multiple puncture technique in the skin with a bifurcated needle. The live vaccine virus is shed from the vaccination site and can spread to other parts of the body or to other people. Therefore, appropriate care of the vaccination site is required until it is completely healed, which may take four weeks or longer. This is particularly relevant if the individual receiving the vaccine comes into direct contact with immunocompromised individuals, who can be infected with the vaccine virus and experience serious complications.

ACAM2000 may cause myocarditis (inflammation of the heart muscle) and pericarditis (inflammation of tissue surrounding the heart). In studies, about 1 in every 175 persons who got the vaccine for the first time may have experienced myocarditis and/or pericarditis. Other serious side effects of ACAM2000 include swelling of the brain or spinal cord, problems with the vaccination site becoming infected, and accidental infection of the eye with the vaccine virus.

FDA to Provide Updates as Developments Occur

The FDA will provide updates as developments occur and will continue to work with federal public health partners and industry to ensure timely access to all available medical countermeasures against monkeypox. More information can be found on the agency’s monkeypox webpage.

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