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22 September 2024 – In a concerning development amid the ongoing global Mpox outbreak, two separate studies have revealed that the efficacy of Bavarian Nordic’s Modified Vaccinia Ankara-Bavarian Nordic (MVA-BN) vaccine against the deadly disease significantly declines within 6 to 12 months post-vaccination.
The MVA-BN vaccine, a two-dose regimen administered four weeks apart, was the first Mpox vaccine to be prequalified by the World Health Organization (WHO). It has been widely used for active immunization against smallpox, Mpox, and related orthopoxvirus infections in adults aged 18 and older. However, recent research suggests that the vaccine’s ability to generate a long-lasting immune response may not be as robust as initially believed.
Study Findings: Waning Immunity
The first study, published in the Eurosurveillance journal, demonstrated a troubling trend. Conducted by researchers at Erasmus University Medical Center in the Netherlands, the study found that “orthopoxvirus-specific binding and MVA-neutralising antibodies waned to undetectable levels” within a year among at-risk individuals who had received two doses of the MVA-BN vaccine.
The research team analyzed 118 participants, including 99 high-risk men who have sex with men (MSM) and 19 laboratory workers. The study included individuals born both before and after 1974, when smallpox vaccinations ceased in the Netherlands. It was observed that, while those previously vaccinated for smallpox retained detectable antibodies for decades, those without pre-existing immunity saw a rapid decline in antibodies within a year.
“These findings highlight the importance of continuous surveillance to monitor the real-world impact of declining antibody levels post-vaccination,” the study urged.
Second Study: Harvard Research Supports Similar Conclusions
A second study, led by researchers at the Beth Israel Deaconess Medical Center, Harvard Medical School, echoed similar concerns. Though yet to undergo peer review, the preprint study showed that antibody responses in individuals vaccinated with MVA-BN largely diminished after 6 to 12 months.
Dan Barouch, director of the Center for Virology and Vaccine Research at Harvard, and his team collected serum samples from 45 participants, including individuals with confirmed Mpox infections and those who had received either one or two doses of the vaccine. The results revealed that antibody levels in participants with two doses of the vaccine were comparable or even lower than peak levels in those who had only received one dose.
This sharp decline in antibody levels raises questions about the long-term protection offered by the vaccine.
Implications for Public Health Strategy
These findings come at a critical time when public health officials are grappling with the global spread of Mpox. According to a recent study published in the British Medical Journal, the efficacy of two doses of the MVA-BN vaccine ranges from 36% to 86%, while a single dose offers only 58% protection.
With evidence pointing to the rapid waning of immunity, health experts may need to reconsider booster strategies and extended vaccination schedules, particularly for high-risk populations. Further research is essential to understand how the loss of antibodies impacts real-world protection against Mpox and whether booster doses can restore or sustain immunity over time.
The Mpox outbreak has raised concerns due to the virus’s potential for severe outcomes, especially in immunocompromised individuals. As vaccination remains one of the most critical tools in controlling the spread, these new revelations underscore the need for vigilant monitoring and adaptive vaccination strategies to prevent a resurgence of the disease.
Conclusion
The waning efficacy of the MVA-BN vaccine after one year, as highlighted by twin studies, emphasizes the necessity of continuous evaluation of immunization protocols in response to emerging diseases like Mpox. Public health authorities worldwide may need to revise current vaccination guidelines to ensure lasting protection, particularly for those at the highest risk.
As global health organizations grapple with these findings, the importance of timely surveillance, booster dose administration, and further research cannot be overstated.
