Mpox, a viral illness caused by the monkeypox virus, has prompted public health agencies to issue specific vaccination guidelines to control its spread. The global outbreak that began in 2022 highlighted the need for targeted immunization strategies to protect those most likely to be exposed. Recommendations are tiered based on the level and type of risk an individual faces. This guidance distinguishes between preventative vaccination for those at sustained risk, reactive vaccination following a known exposure, and specialized vaccination for occupational hazards.
Criteria for Prophylactic Vaccination
Vaccination before a known exposure, known as Pre-Exposure Prophylaxis (PrEP), is recommended for individuals whose behaviors or circumstances place them at a higher, ongoing risk of infection. This strategy aims to establish protective immunity ahead of time, lowering the chance of contracting the virus if an exposure occurs. PrEP eligibility focuses primarily on behavioral factors in areas where Mpox transmission is occurring.
PrEP eligibility includes individuals of any sex or gender who meet specific criteria related to sustained risk within the past six months:
- Having multiple sexual partners.
- Engaging in anonymous sexual contact.
- Having sex at commercial venues or large public events where intimate physical contact is common.
- Exchanging sex for currency or other goods.
Individuals living with Human Immunodeficiency Virus (HIV) are also advised to seek prophylactic vaccination. The guidelines extend to anyone currently eligible for or receiving HIV PrEP medication, recognizing a shared risk profile for sexually transmitted infections. This preventative approach helps shield vulnerable populations who may face a higher risk of severe illness if infected.
Vaccination After Confirmed Exposure
For individuals who have recently been in close contact with someone diagnosed with Mpox, Post-Exposure Prophylaxis (PEP) is employed. The goal of PEP is to prevent the onset of illness or significantly reduce the severity of symptoms by administering the vaccine shortly after exposure. The effectiveness of this approach depends heavily on how quickly the vaccine is given following the potential infection event.
The greatest chance of preventing the disease occurs when the vaccine is administered within four days of the last exposure. Vaccination may still offer some protection by reducing the severity of symptoms if given between four and 14 days after the exposure event. After 14 days, the benefits of vaccination are less certain, requiring healthcare providers to assess the situation on a case-by-case basis.
Close contact is generally defined as:
- Prolonged face-to-face contact.
- Intimate physical contact (including sexual contact).
- Handling contaminated materials without proper protective equipment.
- Sharing bedding and clothing with an infected person.
Any individual identified as a high- or intermediate-risk contact of a confirmed Mpox case should be offered the vaccine as part of this reactive strategy.
Recommendations for Occupational Risk
Certain professions carry a distinct risk of exposure to orthopoxviruses, necessitating vaccination independent of community transmission risk. The Advisory Committee on Immunization Practices (ACIP) advises pre-exposure vaccination for specific occupational groups. This includes research laboratory personnel who directly work with cultures or animals infected with Mpox or other orthopoxviruses.
Clinical laboratory staff who perform diagnostic testing involving handling orthopoxvirus specimens are also advised to be vaccinated. Health care personnel are generally not recommended for routine vaccination unless they are part of a designated response team or are actively involved in administering the ACAM2000 vaccine. Frontline clinicians and general clinical laboratory workers who follow standard infection control protocols are not routinely advised to seek immunization based on occupational risk alone.
Vaccine Types and Administration
The primary vaccine used for both preventative (PrEP) and post-exposure (PEP) strategies against Mpox is JYNNEOS, a two-dose, live, non-replicating viral vaccine. JYNNEOS is preferred for its favorable safety profile, making it suitable for immunocompromised individuals, including those with HIV. The other available vaccine, ACAM2000, is a live, replicating virus vaccine typically reserved for limited circumstances due to its extensive side effect profile and contraindications.
The standard JYNNEOS regimen consists of two doses administered 28 days apart. Peak immunity is generally expected to develop about 14 days after the second dose is received. The vaccine is administered as a 0.5 mL dose via subcutaneous injection into the fatty tissue beneath the skin, typically in the upper arm.
In times of limited vaccine supply, an alternative regimen involving an intradermal injection of 0.1 mL may be used for adults. For the best long-term protection, it is important to complete the two-dose series, even if the second dose is delayed past the four-week mark. While a single dose may offer some protection, the two-dose sequence provides a stronger and more durable immune response.