The emergence of monkeypox in several African countries is straining the world’s capacity to manufacture and distribute vaccines to combat the threat. New options are needed, and a study published Wednesday suggests another one may be on the horizon.
Vaccine maker Moderna reported in the journal Cell that a mRNA vaccine it is developing was more protective than a vaccine made from the same platform as Bavarian Nordic’s Jynneos vaccine in a study in which nonhuman primates were vaccinated and then deliberately infected with mpox.
All animals vaccinated with either vaccine survived what would otherwise have been a fatal challenge with an injection of the MPOX virus, the study reported. But four of the six primates that received the vaccine formulated to mimic the Jynneos vaccine still developed enough lesions to meet the World Health Organization’s criteria for “severe” disease (more than 250 lesions).
None of the macaques that were vaccinated with Moderna’s experimental vaccine, mRNA-1769, developed even “severe” disease (more than 100 lesions).
The vaccine targets four proteins found in all known poxviruses that are critical to the poxvirus life cycle, said Galit Alter, Moderna’s vice president of immunology research and lead author of the study. While other pox vaccines use whole, weakened viruses to generate protection, mRNA-1769 focuses the immune response on these four key targets, Moderna scientists said.
Existing approved mpox vaccines are made from live but weakened vaccine viruses. Vaccinia is a member of the poxvirus family; vaccination with this vaccine provides protection against related viruses. In addition to being used to protect against mpox, vaccinia-based vaccines are also being stockpiled as protection against a bioterrorist attack involving the smallpox virus, a more dangerous poxvirus that was declared eradicated in 1980.
ACAM2000 cannot be given to people who are immunocompromised, which would make it difficult to roll out the vaccine in places where people are living with poorly or uncontrolled HIV.
A trial to determine the safety, tolerability and ability of mRNA-1769 to trigger an immune response in people is underway in the United Kingdom. This phase 1/2 trial, which has enrolled 350 people, began last year. Some results could be available before the end of this year, or in 2025, Moderna said.
In late August, the WHO declared an outbreak of MPOX in Africa a public health emergency of international concern, the second time the virus has triggered a PHEIC in two years. Last week, the global health agency unveiled a six-month plan to combat transmission of the virus.
MPOX, endemic to parts of West and Central Africa, is carried by certain rodents and possibly other small animals. When people are infected, they develop raised, pus-filled lesions that eventually heal. Most people survive, but the disease can be fatal, especially in young children and people with weakened immune systems.
Historically, infections occurred in people – often children – who trapped and handled infected animals, with limited spread within households or communities.
