Vaccination

Vaccines

Two vaccines may be used to prevent mpox:

• JYNNEOS® vaccine is used to prevent smallpox and mpox among people at high risk for infection. During the current mpox outbreak, JYNNEOS is the only vaccine being used in the U.S.
• ACAM2000® vaccine is used to prevent smallpox among people at high risk for infection. It has not been used in the current outbreak.

JYNNEOS is a third-generation vaccine based on a live, attenuated orthopoxvirus, Modified Vaccinia Ankara (MVA). MVA is a live virus that does not replicate efficiently in humans. JYNNEOS is known internationally as Imvamune® or Imvanex®; it is manufactured by Bavarian Nordic. It is fully licensed in the U.S. for subcutaneous administration in individuals 18 years of age and older. In addition, the U.S. Food and Drug Administration (FDA) issued an Emergency Use Authorization (EUA) in August 2022 to allow JYNNEOS vaccine to be used:

• By intradermal injection for prevention of mpox disease in individuals 18 years of age and older determined to be at high risk for mpox infection, and
• By subcutaneous injection for prevention of mpox disease in individuals younger than 18 years of age determined to be at high risk for mpox infection.

ACAM2000 is a second-generation vaccine that contains a live vaccinia virus that replicates efficiently in humans. It is manufactured by Emergent Bio Solutions and is indicated for the prevention of smallpox. It has been made available for use against mpox in the current outbreak under an Expanded Access Investigational New Drug (EA-IND) protocol, which requires informed consent along with completing additional forms. Available evidence supporting the use of smallpox vaccine for mpox prevention is derived from experience with Dryvax®, the vaccine used during smallpox eradication. Dryvax was a first-generation smallpox vaccine manufactured by Wyeth Laboratories. Routine use of this vaccine ended in the United States in 1972, and smallpox was declared eradicated globally in 1980 by the World Health Assembly.  The license for Dryvax was withdrawn in 2008 and no supplies of this vaccine remain.

Although the United States has a large supply of ACAM2000, this vaccine has more side effects and contraindications than JYNNEOS. Therefore, JYNNEOS should be used for people who are at high risk for severe disease caused by infection with mpox virus including, but not limited to, people with human immunodeficiency virus (HIV) infection or other immunocompromising conditions. At this time, the safety of JYNNEOS in pregnant people and children has not been studied. Therefore, the risks and benefits should be weighed in the decision to vaccinate.

Components of the U.S. National Mpox Vaccination Strategy

The U.S. national mpox vaccine strategy was announced on June 28, 2022. Multiple federal agencies, including the Administration for Strategic Preparedness and Response (ASPR), U.S. Food and Drug Administration (FDA), National Institutes of Health (NIH), and Centers for Disease Control and Prevention (CDC) are coordinating to implement this national vaccination strategy.

Mpox vaccine can be given as post-exposure prophylaxis (PEP) both to people with known or presumed exposure to mpox virus. PEP can also be given to people with certain risk factors and recent experiences that might make them more likely to have been exposed to mpox. As PEP, vaccine should be given as soon as possible, ideally within four days of exposure; administration 4 to 14 days after exposure may still provide some protection against mpox and should be offered.

When combined with other prevention measures, vaccination prior to exposure and PEP strategies might help control outbreaks by reducing transmission of mpox virus, preventing disease, or reducing disease severity.

Currently, CDC does not recommend routine immunization against mpox for the general public. Recommendations by the Advisory Committee on Immunization Practices (ACIP) are available for laboratory personnel and health care worker response teams designated by appropriate public health and antiterror authorities who may be at risk for exposure to orthopoxviruses.

Based on available data from the current outbreak, CDC also recommends vaccinating additional populations with risk factors for exposure to mpox virus. Disproportionately affected populations should remain the focus of the current vaccination efforts.

Mpox vaccination should be offered to people with the highest potential for exposure to mpox, including:

• Gay, bisexual, and other men who have sex with men, and transgender or nonbinary people (including adolescents who fall into any of the aforementioned categories) who in the past 6 months have had:
  • A new diagnosis of one or more sexually transmitted diseases (e.g., chlamydia, gonorrhea, syphilis); or
  • More than one sex partner.
• People who have had any of the following in the past 6 months:
  • Sex at a commercial sex venue; or
  • Sex in association with a large public event in a geographic area where mpox transmission is occurring.
• Sexual partners of people with the above risks.
• People with HIV infection or other causes of immunosuppression who have had recent or anticipate potential mpox exposure.

To be most effective, mpox vaccination should be included as part of broader prevention activities and sexual health care. Such efforts should have health equity principles as a foundation and include strategies such as allowing individuals to self-attest vaccine eligibility (i.e., providing mpox vaccination without requiring individuals to specify which criterion they meet), community outreach, holding vaccination events on-site in locations where groups of people disproportionately impacted by mpox may convene, education efforts, and communication about behavioral strategies to minimize risk. Mpox vaccination strategies are likely to be most effective when designed and implemented in partnership with communities and groups that are disproportionately affected. As the epidemiology of the outbreak evolves and new data become available, interim guidance on mpox vaccination will be updated.

Table 1. Components of the U.S. National Mpox Vaccination Strategy Used in the U.S. Mpox Outbreak

*People at risk for occupational exposure to orthopoxviruses include research laboratory personnel working with orthopoxviruses, clinical laboratory personnel performing diagnostic testing for orthopoxviruses, and orthopoxvirus and health care worker response teams designated by appropriate public health and antiterror authorities. (see ACIP recommendations).

†JYNNEOS is considered safe in persons with HIV infection, although effectiveness may be lower among severely immunocompromised individuals. ACAM2000 should not be used in certain people, including those with advanced HIV disease or other causes of immunosuppression, who are pregnant, or who have certain heart conditions.

Timing of PEP

CDC recommends initiating PEP vaccination as soon as possible after someone is exposed to mpox, ideally within 4 days. However, PEP administered between days 4 and 14 after exposure has been shown to be effective and should be offered.

After 14 days, clinicians should consider the benefits of receiving vaccine on a case-by-case basis; benefits might still outweigh risks when administering vaccine in some clinical situations (e.g., for a severely immunosuppressed person with a recent sex partner confirmed to have mpox).

Any person with ongoing risk of exposure to mpox according to the criteria in Table 1 should be offered vaccination, even if previously exposed, and regardless of time since exposure, as long as they have not yet developed signs or symptoms of mpox.

Vaccination given after the onset of signs or symptoms of mpox, after a diagnosis of mpox, or after recovery from mpox is not expected to provide benefit. At this time, naturally acquired mpox is believed to confer immune protection, although duration of immunity is unknown.

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Planning Considerations for Health Departments and Providers

Vaccine Access Considerations

• Both vaccines are available from the Strategic National Stockpile (SNS) by jurisdictional request
• Potential adult or pediatric use of ACAM2000 and potential pediatric use of JYNNEOS should be considered in consultation with CDC
• Either JYNNEOS or ACAM2000 can be used in accordance with the national vaccination strategy, following risk-benefit discussions and a review of any conditions that could increase risk for serious adverse events
• When developing vaccine distribution plans, jurisdictions should consider the current epidemiology of the outbreak as well as health equity considerations
• When developing vaccine distribution plans, jurisdictions should plan for and if feasible, schedule, second doses.

Health Equity Considerations

• Engage people from affected communities in planning for vaccine programs and as trusted sources of information about both mpox and vaccination
• Use non-stigmatizing, plain language in all forms of communication (e.g., printed materials and in-person communication), in the preferred language of the individual
• Reduce barriers to vaccination by allowing individuals to self-attest to meeting criteria to receive mpox vaccine (i.e., provide mpox vaccination without requiring individuals to specify which criterion they meet)
• Have both subcutaneous and intradermal vaccine administration options available on site so that those unable or unwilling to receive the intradermal regimen can receive the subcutaneous regimen
• Reiterate privacy of information and how data will be used, and who will have access to data
• Engage diverse partners already working with affected populations
• Bring vaccines to where affected populations live and work through pop-up events and mobile outreach conveniently located in their communities and neighborhoods
• Offer multiple appointment times and flexible walk-in opportunities, including on evenings and weekends, to improve vaccine accessibility
• Leverage clinical venues (e.g., Federally Qualified Health Centers) that serve people who have historically had less access to primary care, including sexual health clinics, transgender health clinics, and pharmacies
• Use multiple channels, such as, social media, websites, television/radio announcements, or flyers to advertise and book appointments
• Implement equity interventions that prioritize populations less able to access vaccine (e.g., low income or rural communities) even if a first-come, first-served model is used