*CDC has clinical guidance for smallpox vaccine use in a post-event vaccination program. In a public health emergency involving smallpox, vaccination with replication-competent (ACAM2000) smallpox vaccine would be the optimal post-exposure vaccination strategy for stopping the chain of transmission and achieving epidemic control. This is because ACAM2000 is a replication competent vaccine that produces a rapid immune response in comparison to JYNNEOS (also known as Invamune) which requires two doses, four weeks apart to achieve a comparable immune response. Replication competent vaccinia vaccine (DRYVAX) from which ACAM2000 was derived was utilized in a ring vaccination strategy to eradicate smallpox. Optimally data from the eradication campaign shows that post-exposure vaccination less than three days after exposure is optimal for prevention but vaccination greater than three days after exposure to the virus may still decrease morbidity and mortality. For more details see the referenced CDC clinical guidance particularly for algorithms of when to utilize ACAM2000 versus JYNNEOS in relation to absolute and relative contraindications to ACAM2000.              

**JYNNEOS has been the dominant vaccine utilized in the U.S. instead of ACAM2000 because of the lesser adverse event profile. For PEP vaccination, CDC guidance recommends that JYNNEOS should be given as soon as possible, ideally within four days of exposure; administration four through 14 days after exposure may still provide some protection against Mpox.

*** The FDA licensed indication for ERVEBO is for the prevention of endemic disease caused by Zaire ebolavirus. ACIP recommends ERVEBO as PrEP for those responding to an outbreak of Ebola, who work as laboratorians and support staff working at biosafety level 4 (BSL-4) or Laboratory Response Network facilities in the United States that handle specimens that contain or might contain replication-competent EBOV, or Healthcare personnel (HCP) at federally designated Ebola Treatment Centers or state-designated Special Pathogens Treatment Centers involved in the care and transport of patients infected or suspected to be infected with EBOV. ERVEBO is not planned for commercial marketing but is maintained in the Strategic National Stockpile (SNS). The CDC will provide ERVEBO when requested by licensed healthcare providers from institutions or sites with individuals who meet the eligibility criteria (see https://www.cdc.gov/vhf/ebola/clinicians/vaccine/vaccine-request.html  for request instructions). CDC also has an ERVEBO IND program to administer booster doses in individuals who were previously vaccinated with ERVEBO (e.g., ≥ six months since prior vaccination) and are at potential occupational risk for exposure to Zaire ebolavirus (see https://www.cdc.gov/vhf/ebola/clinicians/vaccine/booster-request.html for request instructions). ERVEBO has efficacy when given post-exposure to contacts of cases (and contacts of contacts in a ring vaccination strategy) in endemic Zaire ebolavirus outbreaks. ERVEBO has also been administered post-exposure to health care workers who have had occupational exposure during natural outbreaks.

**** Dosage Regimens of Oral Ribavirin Recommended or Used for Post-exposure Prophylaxis Following Exposure to Hantaviruses, Lassa fever (LF), and CCHF Viruses in Adults1