Monkeypox and Smallpox Vaccine Guidance

When properly administered before exposure to monkeypox vaccines are effective at protecting people against monkeypox.

ACAM200 and JYNNEOSTM (also known as Imvamune or Imvanex) are the two currently licensed vaccines in the United States to prevent smallpox. JYNNEOS is also licensed specifically to prevent monkeypox.

ACAM2000 is administered as a live virus preparation that is inoculated into the skin by pricking the skin surface. Following a successful inoculation, a lesion will develop at the site of the vaccination. The virus growing at the site of this inoculation lesion can be spread to other parts of the body or even to other people. Individuals who receive vaccination with ACAM2000 must take precautions to prevent the spread of the vaccine virus.

JYNNEOSTM is administered as a live virus that is non-replicating. It is administered as two subcutaneous injections four weeks apart. There is no visible “take” and as a result, no risk for spread to other parts of the body or other people. People who receive JYNNEOS TM are not considered vaccinated until they receieve both doses of the vaccine.

CDC, in conjunction with the Advisory Committee on Immunization Practices (ACIP), provides recommendations on who should receive smallpox vaccination in a non-emergency setting. At this time, vaccination with ACAM2000 is recommended for laboratorians working with certain orthopoxviruses and military personnel. The ACIP is currently evaluating JYNNEOSTM for the protection of people at risk of occupational exposure to orthopoxviruses in a pre-event setting.

Vaccine Effectiveness

Because monkeypox virus is closely related to the virus that causes smallpox, the smallpox vaccine can protect people from getting monkeypox. Past data from Africa suggests that the smallpox vaccine is at least 85% effective in preventing monkeypox. The effectiveness of JYNNEOSTM against monkeypox was concluded from a clinical study on the immunogenicity of JYNNEOS and efficacy data from animal studies.

Smallpox and monkeypox vaccines are effective at protecting people against monkeypox when given before exposure to monkeypox. Experts also believe that vaccination after a monkeypox exposure may help prevent the disease or make it less severe.

Receiving Vaccine After Exposure to Monkeypox Virus

Vaccination after exposure to monkeypox virus is still possible. However, the sooner an exposed person gets the vaccine, the better.

CDC recommends that the vaccine be given within 4 days from the date of exposure in order to prevent onset of the disease. If given between 4–14 days after the date of exposure, vaccination may reduce the symptoms of disease, but may not prevent the disease.

Clinician demonstrates the use of a bifurcated needle during the 2002 Smallpox Vaccinator Workshop.

Smallpox and monkeypox vaccines are effective at protecting people against monkeypox when given before exposure to monkeypox. Experts also believe that vaccination after a monkeypox exposure may help prevent the disease or make it less severe.

Revaccination After Exposure

Persons exposed to monkeypox virus and who have not received the smallpox vaccine within the last 3 years, should consider getting vaccinated.

The sooner the person receives the vaccine, the more effective it will be in protecting against monkeypox virus.

Vaccine Risks vs. Monkeypox Disease

For most persons who have been exposed to monkeypox, the risks from monkeypox disease are greater than the risks from the smallpox or monkeypox vaccine.

Monkeypox is a serious disease. It causes fever, headache, muscle aches, backache, swollen lymph nodes, a general feeling of discomfort, exhaustion, and severe rash. Studies of monkeypox in Central Africa—where people live in remote areas and are medically underserved—showed that the disease killed 1–10% of people infected.

In contrast, most people who get the smallpox or monkeypox vaccine have only minor reactions, like mild fever, tiredness, swollen glands, and redness and itching at the place where the vaccine is given. However, these vaccines do have more serious risks, too.

Based on past experience, it is estimated that between 1 and 2 people out of every 1 million people vaccinated will die as a result of life-threatening complications from the vaccine.