CDC recommends preexposure vaccination, JYNNEOS, for at-risk occupational exposure to orthopoxviruses

June 1, 2022

The Centers for Disease Control and Prevention (CDC) have issued a reminder that certain laboratorians and healthcare personnel can be exposed to orthopoxviruses through occupational activities; because orthopoxvirus infections resulting from occupational exposures can be serious, the Advisory Committee on Immunization Practices (ACIP) has continued to recommend preexposure vaccination for these persons since 1980, when smallpox was eradicated.

 In 2015, ACIP made recommendations for the use of ACAM2000, the only orthopoxvirus vaccine available in the United States at that time. During 2020–2021, ACIP considered evidence for use of JYNNEOS, a replication-deficient Vaccinia virus vaccine, as an alternative to ACAM2000. In November 2021, ACIP unanimously voted in favor of JYNNEOS as an alternative to ACAM2000 for primary vaccination and booster doses, according to a CDC news release.

With these recommendations for use of JYNNEOS, two vaccines (ACAM2000 and JYNNEOS) are now available and recommended for preexposure prophylaxis against orthopoxvirus infection among persons at risk for such exposures.

Orthopoxviruses are large, double-stranded DNA viruses (Genus Orthopoxvirus, Family Poxviridae) that comprise multiple species, including Variola virus, Vaccinia virus, Monkeypox virus, Cowpox virus, and newly discovered species (e.g., Akhmeta virus and Alaskapox virus). Infection with an orthopoxvirus or immunization with an orthopoxvirus vaccine lends immunologic cross-protection against other viruses in the genus. Until 1971, children in the United States received an orthopoxvirus vaccine (to prevent smallpox) as part of their routine childhood vaccines. However, with the World Health Organization (WHO) declaration of the eradication of smallpox (the infection caused by Variola virus) in 1980, recommendations for routine vaccinations ended worldwide.

A small subset of persons in the United States continues to receive orthopoxvirus vaccination: persons at occupational risk for exposure to orthopoxvirus infections and certain U.S. military personnel. The first group (those with occupational risk for exposure) are within the purview of ACIP and the focus of this report. Regular booster doses are recommended for persons with ongoing occupational risk for exposure to orthopoxvirus infections. Designated public health and healthcare worker response teams approved by public health authorities should receive booster vaccination only at the time of an event, rather than at regular intervals.

Poxviruses are increasingly being used in a wide range of biomedical research. Vaccinia virus is the most frequently studied poxvirus and serves as the prototype of the orthopoxvirus genus. This orthopoxvirus is used in basic virologic research, and because of its ability to serve as a vector for the expression of foreign genetic material, it is often used as an immunology tool and potential vaccine vector. Vaccinia virus is considered one of the less virulent orthopoxviruses.

In addition to less virulent viruses like Vaccinia virus, some researchers work with more virulent orthopoxviruses, including Variola virus (in some CDC laboratories) and Monkeypox virus. ACIP has historically recommended more frequent booster vaccination doses for persons working with more virulent orthopoxviruses than for those working with less virulent orthopoxviruses.

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