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• Posted September 4, 2024

Moderna's mRNA- Based Mpox Vaccine Shows Promise in Monkey Trial

Current vaccines against mpox were designed to fight an older, rarer cousin of the virus, smallpox.

Now, new research from the drug company Moderna suggests its new mpox vaccine, based on mRNA technology, might do a better job at shielding recipients from harm.

The findings were published Sept. 4 in the journal Cell.

“With the mRNA vaccine, we're able to pick pieces of the virus that can give the most potent and most effective immune response,” senior study author Galit Alter, a virologist and immunologist at Moderna, explained in a journal news release.

“By doing that instead of being distracted by an entire virus, you're able to narrow down on the pieces of the virus that give you protection," she said.

In July 2022, an outbreak that originated in Africa spread worldwide, affecting nearly 100,000 people, primarily gay and bisexual men, across 116 countries and killing about 200 people.

Timely use of the Jynneos mpox vaccine, along with behavioral change among members of the gay male community worldwide, helped ease that outbreak.

However, in recent months a new outbreak of mpox has ravaged much of central Africa, especially the Congo.  According to the Africa Centers for Disease Control and Prevention, the new outbreak has led to more than 21,300 confirmed and presumed mpox cases and 590 deaths in 12 countries, some of which have never been affected by the disease before.

So, any new tool that can shield people at risk against mpox is welcome.

Current vaccines, such as Jynneos, rely on whole but weakened forms of a smallpox-like virus to protect against that (now nearly eliminated) disease.

While effective, vaccines like these provide less than perfect protection against viruses such as mpox, the researchers explained.

Moderna's new candidate vaccine, called mRNA-1769, is targeted to only those bits of the mpox virus' structure that give recipients lasting, protective immune responses that ward off mpox infection and severe disease.

In the new study, Alter and colleagues tested the Moderna mRNA vaccine against the older form of vaccine in a group of 18 macaque monkeys exposed to the mpox virus.

Six of the primates received the older type of vaccine, six received the experimental Moderna mRNA vaccine, and six more monkeys were left unvaccinated.

Eight weeks later, all of the macaques were exposed to a potentially lethal strain of mpox.

The health of all the animals was then monitored for four weeks, including blood samples taken to gauge immune responses.

According to the researchers, all 12 of the vaccinated monkeys survived mpox exposure, regardless of which vaccine they had received.

However, animals that got the mRNA shot were less ill: They lost less weight than the monkeys that got the older vaccine and had fewer of the skin lesions characteristic of mpox (an average 54 versus 604 lesions maximum per animal, respectively), the researchers said.

The animals that got the mRNA shot also had 10 fewer days in which lesions were present, Alter and his team noted. That points to a lessening of the potential for infection transmission, they said.

As for the immune response, blood tests from monkeys that got the mRNA vaccine showed higher numbers of antibodies targeted to the virus, as well as antibodies with more varied immune function, compared to monkeys who got the older vaccine.

In contrast, five of the six monkeys who received neither vaccine died from their exposure to mpox, the researchers noted.

The new mRNA vaccine could also help shield against the family of Orthopoxviruses, of which mpox is a member, the research suggested.

“We tested serum [blood] from the monkeys immunized with this vaccine against basically every Orthopoxvirus we could get our hands on,” said study co-first author Alec Freyn, a virology researcher at Moderna. “It neutralized not only mpox but also vaccinia, cowpox, rabbitpox, camelpox, and ectromelia virus. We believe that this vaccine may protect from other Orthopoxvirus threats that may emerge in the future.”

According to the news release,  mRNA-1769 is already being tested in a phase 2 human trial "to determine the safety, tolerability and immune response of a range of doses."

The primate study was funded jointly by Moderna and the U.S. National Institutes of Health.

More information

Find out more about mpox at the World Health Organization.

SOURCE: Cell Press, news release, Sept. 4, 2024