Two vaccines available
Two vaccines are currently available. The oldest is ACAM2000, a replication-competent vaccine that replaced Dryvax, whose use was stopped in 1977, the last year in which naturally occurring cases of smallpox occurred. ACAM2000 is used to immunize military recruits. It was produced by Sanofi and is now produced by Emergent Biosolutions. Being a live vaccinia vaccine, it is contraindicated for people who are immunocompromised or pregnant, as well as for children and those with eczema, because serious and occasionally fatal reactions have occurred. Because of unexpected cardiac complications in first responders who received Dryvax, having a history of cardiac disease or significant risk factors is considered a contraindication to replication-competent (live) vaccination except in the setting of a bioterrorism event.
ACAM2000 is not FDA approved for monkeypox, but it is readily available. The United States stockpile has more than 100 million doses, according to the CDC.
“ACAM is not very different from Dryvax in terms of safety profile,” Melvin Sanicas, MD, a vaccinologist and health educator, told this news organization.
The newest option is a replication-deficient modified vaccinia Ankara vaccine called Jynneos in the United States (Imvanex in Europe; Imvamune in Canada). The vaccine is made by Denmark-based Bavarian Nordic. The FDA approved Jynneos in 2019. It, too, is available through BARDA’s stockpiles; 1,000 doses are available now and more are on order.
In the current monkeypox outbreak, Jynneos has been offered to higher-risk contacts in the United Kingdom. The CDC is planning to provide it to high-risk contacts of infected persons in the United States. This strategy is called “ring vaccination,” through which only close contacts are immunized initially. The rings are then enlarged to include more people as needed. Ring vaccination works well for easily identified diseases such as monkeypox and in situations in which there are few cases. It has been used very effectively for smallpox and Ebola.
Jynneos is not associated with the same risks as the live vaccine. In solicited reactions, injection-site reactions were common. Other reported systemic symptoms were muscle pain (42.8%), headache (34.8%), fatigue (30.4%), nausea (17.3%), and chills (10.4%).
Other vaccines are expected to be developed. Moderna has just thrown its hat into the ring, announcing it is beginning preclinical trials for monkeypox.
Prolonged close contact
Monkeypox is spread by large droplets or contact with infected lesions or body fluids. It’s thought to require prolonged close contact. In an email interview, Dr. Sanicas told this news organization that the “contact can be with (1) skin lesions of an infected person, (2) respiratory droplets in prolonged face-to-face contact, (3) fomites. The cases in the United Kingdom are in men having sex with men, but it does not mean the disease is now sexually transmitted. People do not need to have sex to be infected, but of course, sexual contact means there is prolonged contact.” The household transmission rate is less than 10%.
Dr. Sanicas confirmed that, as with smallpox, monkeypox could be transmitted by contact with clothing or bedding that has been contaminated through contact with the infected lesions, as smallpox was transmitted to Native Americans by colonizers. Airborne transmission is a theoretical possibility but is not considered likely. Being a DNA virus, monkeypox is less likely to mutate than COVID. “If it were as infectious as flu or coronavirus, there would be more infections and outbreaks in countries where MPX [monkeypox] is endemic in Western Africa or Congo Basin,” said Dr. Sanicas.
Fortunately, this clade of monkeypox, which appears to have originated in West Africa, is estimated to have a mortality rate of about 1%. In contrast, the Congo Basin clade has a death rate of up to 10%.
Dr. Sanicas concluded, “Be cautious, but there’s no need for further fear and panic on top of what we have for COVID-19. Monkeypox is not COVID and will not cause the same devastation/death/lockdowns as COVID-19.”
Dr. Hruby is an employee and stockholder of SIGA. Dr. Sanicas reports no relevant financial relationships.
A version of this article first appeared on Medscape.com.