While a JAMA study found a decline in mpox antibody responses after vaccination, a University of Oxford expert cautioned that there is still not enough evidence to determine if this decline also leads to waning protections.
The antibody response from Bavarian Nordic’s mpox vaccine Jynneos appears to weaken six to 12 months after inoculation, raising questions about its use in conferring lasting protection against the virus, according to a research letter published Thursday in the Journal of the American Medical Association.
“Our data suggest that protective immunity may be waning in individuals who were vaccinated with this vaccine in 2022,” study corresponding author Dan Barouch said in a statement.
The observational study involved 45 adults who were given either one or two doses of Jynneos. Three patients who had been diagnosed with mpox infection were also included to serve as comparators. Results showed that in people who were given two vaccine doses, titers of antibodies targeting mpox-related antigens peaked three weeks after the jab but declined to just barely above baseline levels at 12 months.
A similar trend was reported in those who were given just one Jynneos dose—with antibody titers peaking at three weeks—though the overall elicited immune response was weaker.
The researchers pointed out that three months after Jynneos vaccination, titers of mpox serum neutralizing antibodies were “minimal,” regardless of whether study participants received one or two doses. Meanwhile, in patients with confirmed infections, serum neutralizing antibody levels remained high at three months and persisted through nine months.
“These data suggest that protective immunity may be waning in individuals who were vaccinated with MVA-BN (Jynneos) in 2022 and that boosting may be required to maintain robust levels of protective immunity,” the researchers wrote, while noting that their conclusions are limited by the study’s small sample size and observational design.
Jake Dunning, senior research fellow at the University of Oxford’s Pandemic Sciences Institute, said in an expert reaction letter that while the Thursday study is important in that it helps “improve our understanding of real-life use” of new vaccines, it is also “just one piece of a quite complicated jigsaw when it comes to understanding vaccine effectiveness.”
The waning antibody titers after vaccination has long been known and is even predictable, Dunning pointed out. However, the JAMA study “does not provide proof that antibody waning results in waning protection against mpox infection or severe mpox disease in real life,” He wrote, noting that further studies are needed to better elucidate the real-life trajectory of not only a vaccine’s antibody response but also of its overall protective effect.
Despite these emerging questions about Jynneos’ long-term effectiveness, Bavarian Nordic will likely continue to enjoy the mpox outbreak windfall that analysts have predicted. Jefferies analyst Peter Welford wrote in a note to investors that the company’s value “as a standalone vaccine play is underappreciated.”
Welford contends that Bavarian Nordic will “remain firmly profitable” in the coming months and beyond as it reaps various milestones and other payments from Jynneos-related deals. The company last week entered into an agreement with UNICEF to deliver one million doses of the vaccine, which the biotech has pledged that it will make available for supply by the end of the year.
In August 2024, Bavarian Nordic received an order for 175,420 doses of Jynneos from the European Commission’s Health Emergency Preparedness and Response Authority, which will donate the vaccines to the Africa Centers for Disease Control.
