Moderna has announced its mRNA vaccine in development for mpox is more effective than Bavarian Nordics Jynneos in prevention of severe disease.

The news comes after the World Health Organization (WHO) declared a recent outbreak of the virus a public health emergency of international concern (PHEIC). The newest strain, clade Ib has been spreading across African countries, stemming from the Democratic Republic of Congo.

In a paper released in Cell on September 4, Moderna, best known for its mRNA Covid-19 vaccine, announced that mRNA-1769 had been more effective than the Bavarian Nordic Jynneos vaccine, one of the only two marketed mpox vaccines globally, in preventing severe disease and reducing virus levels in monkeys.

The trial involved three groups of monkeys, with six animals in each group. One group received mRNA-1769, one Jynneos and one placebo. Subjects were dosed twice, once on the first day and again four weeks later. Subjects were evaluated daily for 12 weeks.

The vaccine also saw reduced viral replication in the blood and throat, and reduced lesion formation. Researchers believe that the reduced viral replication could lead not only to disease-modifying activity but also to reduced spread.

Moderna is currently running a Phase I/II trial (NCT05995275) of the mpox vaccine in healthy participants in the UK. The data from Phase I/II trial, due in mid-2025 will help to shape the Phase III trial design.

A spokesperson for Moderna says: “Moderna is investigating a potential vaccine for mpox and smallpox in a Phase I/II Study conducted in the UK. Approximately 350 participants have enrolled in the trial across several sites in the UK. Participants were chosen at random to receive two doses of the investigational vaccine or a placebo. The trial is fully recruited, and the dosing of participants has been completed. The trial will last approximately 13-14 months.”

Moderna started development of its candidate in 2022 after the previous PHEIC was called in regards to mpox.

Moderna’s candidate uses four proteins detected in the mpox virus to mimic the virus. This triggers the body to create antibodies to tackle the virus.

BioNTech is also developing a mRNA vaccine for mpox which is also in a Phase I/II study (NCT05988203) due to readout in mid-2025.