Monkeypox Vaccines: Q&A With the CDC's Agam Rao, MD

Two vaccines are available for monkeypox. Vaccine expert Agam Rao, MD, medical officer in CDC's Poxvirus and Rabies Branch, answers questions about their effectiveness and dosing. How effective is the smallpox vaccine against monkeypox, and how was it identified as potentially protective against monkeypox? Smallpox is the illness that is caused by variola virus, a member of the genus Orthopoxvirus. Monkeypox virus is in that same genus. For viruses within the same genus, we expect that a vaccine against one will be effective against the other. There are actually several different vaccines worldwide that are used for smallpox and other similar viruses. In the United States, we have two vaccines that are licensed for the prevention of smallpox: ACAM2000 and JYNNEOS. JYNNEOS happens to be licensed by the US Food and Drug Administration (FDA) for prevention of monkeypox as well. We don't have any reason to believe that either of these vaccines would differ in effectiveness for monkeypox vs smallpox because the two viruses are related. Do you have any data on how effective ACAM2000 and JYNNEOS are in preventing smallpox? JYNNEOS is a new vaccine and therefore was not used during the eradication campaign for smallpox, so we don't have any real-world data on how effective it would be in preventing smallpox. In terms of ACAM2000, its precursor, a drug called Dryvax, was used during the eradication campaign, and data indicated that it was 85% effective at preventing smallpox if it was given as postexposure prophylaxis within 4 days of an exposure. Even beyond that, if the drug was given up to 14 days after an exposure, it would then at least lessen the symptoms. We don't have data about the real-world effectiveness of these vaccines to prevent monkeypox, particularly in this outbreak. Have there been monkeypox cases in older individuals who had been given the smallpox vaccine? There have been cases of people who have gotten monkeypox despite being vaccinated as children or being vaccinated in the past. Vaccine effectiveness probably wanes over time. We are also aware of monkeypox cases in people who had received the JYNNEOS or ACAM2000 vaccine as part of the current outbreak. There's really no vaccine that's 100% effective. There are always going to be people who don't mount an appropriate immune response, either because they're immunocompromised or for any other reason. What data did the FDA look at to approve JYNNEOS for the prevention of smallpox and monkeypox? In addition to the FDA approving the vaccine, the Advisory Committee on Immunization Practices, which is a group of vaccine experts who assemble to provide guidance to the CDC director for national vaccine recommendations, also recommended the JYNNEOS vaccine for the prevention of Orthopoxvirus infection for people with occupational risk. This was in November of last year and was unrelated to the current outbreak.