Jynneos vaccine wane significantly over the course of a year, raising new questions about just how protected vaccinated people are against reinfection and if booster doses of the vaccine are needed among at-risk populations.
The study was released alongside an alarming development in the globalization of mpox: More than 21,000 cases of the virus have been recorded in the past year in the Democratic Republic of the Congo (DRC), UNICEF noted yesterday. On August 14, the World Health Organization declared the DRC outbreak a public health emergency of international concern, in part because around 60% of cases are in children 15 years and under.
In the DRC, children under age 15 account for about half of all suspected cases reported in DRC so far this year but 80% of the deaths, according to UNICEF. This week Rwanda became the first African country to begin mpox vaccination (see today's CIDRAP News story).
Outbreak virus strain 'concerning'
The massive outbreak is fueled by the transmission of clade 1b virus, which is more severe than the clade 2 virus that caused a worldwide outbreak of mpox primarily among men who have sex with men (MSM) in 2022. Now 14 African countries have tracked clade 1b cases, as has Sweden and Thailand.
"People thought the problem was solved with mpox," explained Elizabeth Finley, from the National Coalition of STD Directors. Finley said the United States has seen periodic of upticks of clade 2 infections but no cases of clade 1b yet.
People thought the problem was solved with mpox
"It's concerning we are seeing a new clade in Africa, and then we see a preprint like this that shows waning immunity," she said.
One dose of Jynneos not as protective
As of now, Finley said no official US body, including the Centers for Disease Control and Prevention, is recommending a booster dose of Jynneos.
"For us, continued priority is to get first and second doses. If people are only partially vaccinated they should get that second dose," she said.
Jynneos, developed in 2019 by Bavarian Nordic, is supposed to be administered as two doses given 28 days apart. A live attenuated vaccinia virus vaccine, it targets smallpox and other orthopoxviruses, including mpox.
Efficacy estimates for two doses of the vaccine range from 36% to 86%. Having just one dose, which many Americans were given as a dose-sparing method in the early weeks of the 2022 outbreak, is only about 58% effective in preventing mpox, according to a recent study in the British Medical Journal.
To further assess efficacy, the authors of the preprint study used data from ongoing observational studies of mpox vaccine recipients.
Study author Dan Barouch, MD, PhD, the director of the Center for Virology and Vaccine Research at Beth Israel Deaconess Medical Center, said serum samples were collected from 45 participants who had either confirmed mpox infection of received either one or two doses of Jynneos. All participants were seen at the Beth Israel Deaconess Medical Center in Boston.
Natural infection leads to higher antibodies
Mpox serum neutralizing antibody (NAb) titers were detectable in only a few participants following one or two doses of Jynneos at 3 months, the authors said. In contrast, high titers (median, 965) of mpox NAbs were detected at 3 months following natural infection and persisted at 9 months post-infection (median, 284).
Barouch said the antibody levels confirm previous findings that showed Jynneos provides 66% efficacy as a two-dose regimen and 36% efficacy as a one-dose regimen at peak immunity (3 weeks) during the 2022 mpox outbreak.
Vaccine-generated mpox antibodies largely waned after 6 to 12 months, he said, and at 12 months, antibody levels in participants who had two doses of vaccine were comparable or lower than peak antibody responses in people who received one dose of vaccine.
I certainly think the data suggest that protection of immunity might be waning in these individuals.
For now, Barouch said, public health officials must watch the clade 1b story carefully and should further study breakthrough infections in previously vaccinated people.
"We have to see if there are breakthroughs," Barouch said. "I certainly think the data suggest that protection of immunity might be waning in these individuals."
