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Laboratory personnel and those responding to outbreaks of orthopoxviruses, including smallpox and monkeypox, should be vaccinated with Jynneos, finalized recommendations from the CDC's Advisory Committee on Immunization Practices (ACIP) said on Friday.

For healthcare personnel who either administer ACAM2000 or care for patients infected with orthopoxviruses, Jynneos is recommended based on shared clinical decision-making, reported Agam Rao, MD, of the CDC, and colleagues, writing in an early edition of the .

What started off as a mere formality, with a new live, replication-deficient subcutaneous vaccine to replace ACAM2000, a live replicating vaccine (which produces a "take" in those where it's administered), gained new relevance with the recent global monkeypox outbreak.

In a statement, CDC noted that "the new guidelines were not created in response to the monkeypox outbreak," but rather agency experts "have been working to refine usage recommendations during the past two years."

In November 2021, ACIP voted 15-0 to recommend Jynneos as an alternative to ACAM2000 for primary series and booster doses.

ACIP also voted that people at continued risk of exposure to more virulent orthopoxviruses, including monkeypox, should receive a booster with Jynneos every 2 years, including those with continued risk of exposure who received an ACAM2000 primary series.

"Designated public health and health care worker response teams approved by public health authorities should receive booster vaccination only at the time of an event, rather than at regular intervals," the authors wrote.

CDC said that both vaccines (ACAM2000/Jynneos) would be available during the current monkeypox outbreak.

Jynneos consists of two doses given 28 days apart, and vaccine protection is not conferred until 2 weeks following the second dose, the team added. The vaccine is contraindicated for those with an allergy to a vaccine component, though ACAM2000 is contraindicated for those with atopic dermatitis or eczema, those who are immunocompromised, as well as those who are allergic to a vaccine component.

According to Rao's group, data indicate that Jynneos is safe for people with atopic dermatitis or immunocompromising conditions, but cautioned that "such persons might be at increased risk for severe disease if an occupational infection occurs."

While ACAM2000 is contraindicated for pregnant and breastfeeding women, there is insufficient evidence on Jynneos for either population, though the authors noted that animal models showed "no evidence of harm to a developing fetus."

Jynneos has not been evaluated for children under age 18, and the authors advised consulting public health authorities if vaccination is considered for this population. ACAM2000, however, is contraindicated for infants younger than 1 year old.

Individuals with at least three major cardiac risk factors, such as hypertension, diabetes, and hypercholesterolemia, are contraindicated for ACAM2000 due to risk of myopericarditis. However, the authors said that clinical studies have not detected an increased risk for this condition in those receiving Jynneos, and those cardiac patients should be counseled about the "theoretical risk" of myopericarditis.

Rao and co-authors recommended additional data on the duration of protection of the Jynneos vaccine, and research about the frequency of booster doses, as well as potentially co-administering Jynneos with mRNA COVID vaccines.

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