Vaccine Guidance

Two vaccines may be used for the prevention of mpox virus infection: 

• JYNNEOS (also known as Imvamune or Imvanex), licensed (or approved) by the U.S. Food and Drug Administration (FDA) for the prevention of mpox virus infection in adults 18 years and older. On August 9, 2022, the FDA issued an Emergency Use Authorization (EUA) for JYNNEOS for individuals under the age of 18 years old. 
• ACAM2000, licensed (or approved) by FDA for use against Smallpox virus and made available for use against mpox virus under an Expanded Access Investigational New Drug (IND) application. 
• Research on vaccine effectiveness is ongoing, but evidence indicates that JYNNEOS vaccination provides protection against mpox. Initial licensure was supported by animal and clinical studies showing development of antibodies after vaccination. 
  • A CDC MMWR published in December 2022 reported among males in the U.S. aged 18–49 years eligible for vaccination, mpox incidence among unvaccinated persons was 9.6 times as high as that among persons who had received 2 vaccine doses and 7.4 times as high as that among persons who had received only the first dose ≥14 days earlier. 
  • This analysis also suggested no difference in vaccine performance between subcutaneous and intradermal administration. 
• Another CDC MMWR from December 2022 supports JYNNEOS vaccine safety during the current outbreak. 
  • During May 22–October 21, 2022, nearly 1 million JYNNEOS doses were administered in the U.S. The vaccine safety profile was consistent with prelicensure studies. The most common adverse health events reported were non-serious and included injection site reactions. Serious adverse events were rare among adults, and no serious adverse events have been identified among persons aged <18 years. 

JYNNEOS

JYNNEOS is an attenuated live virus vaccine which has been approved or authorized for the prevention of mpox.  

• Visit CDC’s Get Ready and Healthy for Summer webpage to learn more about preparing for spring and summer events that celebrate the LGBTQ+ community. Mpox cases in the United States are becoming increasingly rare, but unvaccinated and under-vaccinated people who could benefit from vaccine may still be at risk. The best protection against mpox occurs 2 weeks after the second shot, so plan ahead and use other strategies to prevent mpox. 
  • It’s not too late to get a second dose of JYNNEOS vaccine even if someone received their first dose months prior. 
  • People who are already vaccinated do not need an additional dose of JYNNEOS vaccine, unless they have ongoing risk because of their job. 
• Dosing:
  • Because JYNNEOS is licensed as a two-dose series, CDC continues to recommend two doses of JYNNEOS vaccine to prevent mpox disease, regardless of how or where it is administered. The two doses should be given 28 days apart.
  • If the second dose is not administered during the recommended interval, it should be administered as soon as possible based on ACIP’s general best practices. There is no need to restart or add doses to the series if there is an extended interval between doses. 
  • Peak immunity is expected 14 days after the second dose. The duration of immunity after one or two doses of JYNNEOS is currently unknown. 
  • The level of protection provided by only one dose is not known. 
• Route of administration: 
  • During this outbreak, the alternative regimen (intradermal route) is preferred, but the JYNNEOS vaccine may be administered subcutaneously using the standard regimen (subcutaneous route).  
  • People of any age with a history of developing keloid scars and individuals younger than 18 years of age should receive the vaccine via the subcutaneous route. 
  •  Patients with concerns about intradermal administration due to potential stigma or other personal reasons should be offered subcutaneous doses.  

• Eligibility: 
  • CDC recommends that healthcare providers 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.
  • As a reminder, vaccines should not be administered after the onset of illness. If a patient develops symptoms consistent with mpox illness at the time of vaccination, the patient is no longer eligible to receive the vaccine, regardless of previous eligibility status. Vaccination given after the onset of signs or symptoms of mpox is not expected to provide benefit. 
  • If a patient has been diagnosed with mpox previously, they are not eligible for vaccination. 
  • If a patient develops mpox before receiving their second dose, they are no longer eligible to receive the second dose.
• For more information about JYNNEOS, please refer to the Package Insert, as well as CDC JYNNEOS Interim Clinical Considerations. 
• For more information and guidance on the EUA for JYNNEOS use for individuals under the age of 18 years old, please refer to the EUA HCP Fact Sheet and the CDC Interim Clinical Considerations . 
• Smallpox/Mpox Vaccine (JYNNEOS) Vaccine Information Statement 

ACAM2000

ACAM2000 contains a live replicating vaccinia virus, licensed by the FDA for immunization in people who are at high risk for smallpox infection. ACAM2000 may be used as an alternative to JYNNEOS vaccine.

• For more information about ACAM2000, please refer to the ACAM2000 Package Insert, as well as CDC ACAM2000 Interim Clinical Considerations
• FDA Medication Guide for ACAM2000 

Interchangeability of Dosing Regimens

Dosing regimens are interchangeable. For example, a person aged 18 years or older who received one JYNNEOS vaccine dose with the standard subcutaneous regimen may receive a second dose with the alternative intradermal regimen at the recommended interval (i.e., 28 days) to complete the vaccination series.  Another example is a person who received the first dose intradermally, had a robust local reaction, and refuses a second dose unless given subcutaneously. In this situation, that second dose can be given subcutaneously.