What do we know about mpox vaccine effectiveness?

With the first case of Mpox clade I found in Canada, experts urge those who got first doses of vaccines to get their second shots to enhance their protection against the virus. Since the new clade affects children and adolescents, researchers have also been studying the vaccine’s effectiveness in the younger population.Mpox clade I may cause more severe disease and initial data suggests it may be more easily transmitted. The first case in Canada was detected in Manitoba in late November in a person who had returned from travel.Read: First Canadian case of more severe mpox strain confirmedNeed for second dose Right now in Canada, mpox clade II has spread mainly in the men who have sex with men population. While cases are fewer than in 2022, the virus is still spreading. “This is not going away,” said Dr. Isaac Bogoch, clinician investigator at the Toronto General Hospital Research Institute. He treated numerous patients with mpox. The disease “hurts like hell,” he said, adding that people were admitted to hospital for pain control alone. Dr. Bogoch spoke about the issue at the Canadian Immunization Conference, held in Ottawa in late November.People who got the first dose should make sure they get their second dose, even if it is past the 28-day recommended time between doses. The vaccine does a remarkable job at reducing symptoms, Dr. Bogoch said. He has treated a few post-vaccination breakthrough infections, but said “they look like nothing.” A case series reported in the Lancet found that breakthrough infections post-vaccination had a shorter duration and fewer average number of lesions. “It’s remarkable to see these vaccines work in practice,” Dr. Bogoch said.Read: Many people at risk never got their 2nd mpox vaccine dose, public health agencies say The vaccine used to combat mpox is a third-generation smallpox vaccine, modified vaccinia Ankara (Bavarian-Nordic) (MVA-BN), marketed as Imvamune. A 2024 systematic review and meta-analysis of vaccine effectiveness for mpox provided good news: a vaccine effectiveness of 76% with one dose and 82% with two doses. An analysis on vaccine effectiveness published in Nature suggests that when the supply of doses is limited, the focus should be on immunizing the largest number of people with one dose. When doses are available a second dose should be given to improve vaccine effectiveness. Will boosters be required? The paper in Nature examines this, but in the end, it’s not clear. “It’s too early to tell,” Dr. Bogoch said. One group the National Advisory Committee on Immunization recommends get vaccinated is people who engage in sex tourism. Attendees at the Canadian Immunization Conference noted that those people aren’t often going to present at your clinic asking for a vaccine. Dr. Bogoch and other experts at the Canadian Immunization Conference agreed that if vaccine is available, it should be given to travellers who ask for it.Dr. Bogoch said that it doesn’t look like it is necessary to give the vaccine to healthcare workers at present. Emerging cladeMpox clade 1b and 1a is spreading in Central Africa and it appears to spread in children and adolescents, said David Kelvin, from the department of microbiology and immunology, at Dalhousie University in Halifax. Kelvin travelled to the Democratic Republic of the Congo to study the spread and genetics of the new clade. He said that in his experience, there’s “an overrepresentation of children in hospital” with this new clade. The World Health Organization (WHO) has data on the demographics of clade I infections, showing the majority of detected cases in DRC are in children aged four and younger.Vaccine for mpox clade IThe thinking is that the MVA-BN vaccine will be effective against clade 1, based on animal and other studies, according to Dr. Christine Navarro, a public health physician with Public Health Ontario and assistant professor at the Dalla Lana School of Public Health at the University of Toronto. A paper in Expert Review of Vaccines also discusses this.With the spread of clade I in children, the question is if MVA-BN is effective in children. Interim results of a study of MVA-BN vaccine show the vaccine stimulates a robust immune response in adolescents, similar to the response produced in adults. The vaccine was well tolerated and there were few adverse events in the younger population.While the MVA-BN vaccine still needs to be fully studied in younger children, Japan has licensed a smallpox vaccine, called LC16m8, for use in children since 1975. It’s not yet available in Canada, said Dr. Navarro. WHO recently gave emergency access to the vaccine, and Japan donated three million doses to the DRC.Read: WHO launches plan to stanch mpox transmission and says the virus can be stopped

What do we know about mpox vaccine effectiveness?

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