Monkeypox is an orthopoxvirus that is related to smallpox. It has been associated with sporadic outbreaks over the past decades. The current outbreak is associated with the less virulent West African clade of the virus, primarily in men who have sex with men and their close contacts, and manifests most commonly as macular pustular lesions at areas on the body exposed to the virus, including as painful lesions in the genital region that can take two to three weeks to completely heal. These lesions may have very high titers of infectious monkeypox virus present, and until the lesions completely heal over, these individuals can potentially spread the virus further to others.
JYNNEOS is the only FDA-licensed vaccine in the United States that is approved for prevention of monkeypox disease. JYNNEOS is also approved for prevention of smallpox disease. 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. It is a live, non-replicating vaccine using Modified Vaccinia Ankara (MVA) virus that 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-licensed live replicating vaccinia virus vaccine approved for the prevention of smallpox disease. It is associated with higher risk of certain serious adverse reactions compared to JYNNEOS.
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. The Expanded Access IND mechanism is also available for use of JYNNEOS against monkeypox in individuals less than 18 years of age.
It should be noted that ACAM2000, which is administered as a single dose, must be given by a multiple puncture technique in the skin with a bifurcated needle, and 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 and pericarditis. 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.
In contrast, JYNNEOS is licensed as a two-dose vaccine, administered by subcutaneous injection. The virus in JYNNEOS is non-replicating, therefore, the vaccine is safe for use in significantly compromised individuals who may not be indicated or recommended to receive certain live attenuated vaccines. The effectiveness of a 2-dose series of JYNNEOS against monkeypox was based on the immune responses of JYNNEOS in humans and data from a monkeypox virus challenge study conducted in non-human primates.
Ensuring that those who are vaccinated are appropriately protected against monkeypox is critical.
Pending any new data that show that two doses of JYNNEOS are not required for adequate protection against monkeypox, we need to rely on the currently approved two-dose regimen at this time to ensure those who receive the vaccine can feel confident in their protection.