A NEW “Covid-style” mpox jab could reduce symptoms and make the bug less deadly.
The most frequently used mpox vaccine provides partial immunity to the disease, but isn’t always able to prevent transmission or stop people developing severe symptoms, scientists said.
A study published in the journal Cell compared the modified vaccinia Ankara (MVA) jab currently being used against mpox to a new mRNA vaccine developed by Moderna.
It uses the same technology as Covid-19 jabs developed by Pfizer/BioNTech and Moderna, which makes harmless proteins look identical to a virus or bacteria and trains the body’s immune system to attack the ‘real’ virus if it encounters it again.
The study found that the new Moderna mpox jab – dubbed mRNA-1769 – was more effective at limiting symptoms and disease duration compared to the original MVA vaccine.
To the test the jabs’ effectiveness, scientists infected macaque monkeys with a lethal strain of the mpox virus.
Author Alec Freyn, a virology researcher at Moderna, said: “This study is the first in a nonhuman primate model where we compare an investigational mRNA mpox vaccine directly to the current standard of care.
“When we put those vaccines head-to-head in primates, we saw improved responses from the mRNA vaccine in terms of not just protection from survival but also fewer lesions, shorter duration of disease, and less viral shedding in the blood and respiratory tract.”
It comes after the World Health Organization (WHO) declared a global health emergency over a new lethal strain of mpox, known as clade Ib.
The new clade is thought to be far more deadly and contagious than its predecessor – clade 2 – that received global attention in 2022.
MVA vaccines, which were originally developed to combat smallpox, contain whole viruses that have been weakened so that they cannot cause disease in humans.
However, this weakening also means that they provide limited protection compared to other vaccines, Moderna researchers said.
By comparison, using mRNA technology means jabs can contain only the parts of the virus that are most likely to induce a lasting immune response, without exposing the person to a whole infectious virus.
Moderna’s new mpox mRNA vaccine contains four viral antigens that the virus needs to attach to and enter host cells.
Senior author Galit Alter, a virologist and immunologist at Moderna, said: “With the mRNA vaccine, we’re able to pick pieces of the virus that can give the most potent and most effective immune response.
“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.”
Scientists vaccinated six macaques with each jab and then exposed to a lethal strain of the mpox virus six weeks later.
They also exposed six unvaccinated macaques to the virus, to serve as a comparison – what’s known as a control group.
Researchers monitored the animals’ health for four weeks and collected blood samples to examine their immune response.
All 12 vaccinated monkeys survived, regardless of which jab they’d been given.
But five of the six unvaccinated control animals died of the disease.
Though both vaccines reduced the disease’s severity, mRNA-vaccinated animals lost less weight and had fewer lesions than MVA-vaccinated animals.
Mpox tends to cause a rash that can spread to any part of the body, which turns into sores or small blisters filled with fluid.
On average, animals in the control group had a maximum of 1,448 lesions, MVA-immunised animals had a maximum of 607 lesions, and mRNA-immunised animals had a maximum of 54 lesions.
Dr Jonas Albarnaz, a research fellow specialising in pox viruses at The Pirbright Institute, said:
“This news of a case of clade 1 mpox in Sweden is concerning for two main reasons.
“First, this is the first clade 1 mpox virus case outside Africa. This indicates that the extent of the international spread of clade 1 outbreak in DRC might be larger than we knew yesterday.
“And second, clade 1 mpox virus is associated with a more severe disease and higher mortality rates than the clade 2 virus responsible for the international mpox outbreak in 2022.
“This is hard to predict whether we will see further cases of clade 1 mpox outside of Africa, but this case in Sweden is a warning call for public health authorities to be vigilant and implement robust surveillance and contact-tracing strategies to detect possible new cases early on.
“It’s also critical to determine what is the link between this clade 1 mpox virus detected in Sweden and the ongoing outbreak in DRC.
The mRNA vaccine also shortened the number of days that animals had lesions for by more than 10 days compared to the MVA vaccine.
Finally, mRNA-vaccinated monkeys had lower amounts of the mpox virus in their blood and throats, suggesting the new vaccine might also be more effective at reducing transmission.
Senior author and virologist of the United States Army Medical Research Institute for Infectious Diseases, Jay Hooper, said: “With the mRNA technology, we’re able to produce a vaccine that gives quite potent responses with a very tolerable safety profile.”
When the researchers compared the immune response triggered by the mRNA and MVA vaccines, they found that the mRNA vaccine resulted in higher numbers of antibodies, as well as antibodies with more diverse immune functions.
The mRNA vaccine may also offer immunity to other Orthopoxviruses – such as smallpox or cowpox – researchers claimed.
By comparison, the MVA vaccine resulted in smaller immune responses that weren’t as effective at neutralising other Orthopoxviruses.
Dr Freyn said: “We tested serum from the monkeys immunised with this vaccine against basically every Orthopoxvirus we could get our hands on.
“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.”
Moderna’s mRNA-1769 vaccine is currently being assessed in a phase 1/2 clinical trial, which tests the safety, side effects and best dosage of a new treatment.
Experts are unsure if the jab credited for helping put an end to the 2022 outbreak will respond to the new, deadlier version of mpox.
Professor Marion Koopmans, of the pandemic and disaster Centre at the Erasmus Medical Centre, said experts don’t know how the new clade 1b mpox virus would react to current jabs.
“The honest answer is we do not know yet,” she said.
Scientists have also warned that the new lethal strain of mpox spotted in several African countries, as well as Asia and Europe is mutating faster than expected.
