An mRNA vaccine for mpox developed by the biotech company Moderna has shown promise in monkeys, raising hopes that it could help to tackle the ongoing outbreak in West and Central Africa. While other vaccines for the virus already exist and helped to bring a global mpox outbreak in 2022 under control, researchers say a new vaccine based on mRNA technology would have a number of advantages.
Nigeria, which has had 35 confirmed cases of mpox so far this year, became the first country in Africa to gain mpox vaccines last week, with the arrival of 10,000 doses of the JYNNEOS vaccine. This shot contains a weakened form of the related vaccinia virus and previously helped high-income countries, such as the UK and US, curb cases during the 2022 outbreak.
mRNA vaccines, which first began being used widely during the covid-19 pandemic, contain instructions for cells to produce viral proteins, so that the immune system can learn to recognise them. Unlike other types of vaccines, they can be developed and manufactured quickly once the genome of a virus has been sequenced.
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at Moderna in Massachusetts and her colleagues created a vaccine containing RNA sequences encoding four proteins that are present in a family of viruses that includes mpox. They gave six macaques the mRNA vaccine and six a so-called MVA vaccine similar to JYNNEOS, while six macaques in a control group were unvaccinated. All the vaccinated animals survived a usually lethal dose of the virus, while five out of six unvaccinated animals died.
The mRNA vaccine also reduced the severity of symptoms. On average, animals that received the mRNA vaccine had a maximum of 54 skin lesions from the virus, while those that received the MVA vaccine had a maximum of 607 lesions and unvaccinated animals had a maximum of 1448 lesions. Animals that received the mRNA vaccine had mpox lesions for more than 10 fewer days on average than those that received the MVA vaccine or that were unvaccinated.
The results are promising and stand a good chance of being replicated in humans, says at the National University of Singapore.
A human trial of the vaccine has already begun, with results expected next year. 鈥淚f the result can be replicated in humans it will be a great result,鈥� says at St. Elizabeth鈥檚 Medical Centre in Boston, Massachusetts.
Although the mRNA approach shows promise, the JYNNEOS vaccine already works very well. One dose prevents caused by the clade II variant that circulated in 2022, while two doses prevent 82 per cent of cases. The vaccine can also reduce the severity of the rash and lesions during infection, but whether it can stem the transmission of the virus is unknown.
The current outbreak involves a different variant of the virus, known as clade Ib, but it is close enough to the earlier variant that the JYNNEOS vaccine should also work well, says at the University of Rwanda.
So is there a real need for mRNA vaccines? All the researchers who spoke to 快猫短视频 agree that they would help. Some fear that as the mpox virus, formerly known as monkeypox, spreads more widely, it could mutate in ways that render existing vaccines less effective. In that case, mRNA vaccines will be needed, says Sah. 鈥淲e don鈥檛 know how the virus will evolve in future,鈥� he says. 鈥淚f it becomes a more severe form, then we need something.鈥�
But others say the potential for new variants to beat existing vaccines isn鈥檛 as big a concern with mpox as it was with covid because the virus doesn鈥檛 evolve as quickly. 鈥淲e have a long history of genetic sequencing of these [mpox] viruses and see that the rate of change is relatively slow,鈥� says at Moderna.
Instead, investing in mRNA vaccines against mpox would help to boost vaccine supplies, as mRNA vaccines can be more quickly produced compared to other vaccines, such as JYNNEOS, that rely on growing whole viruses in the lab, says Ananth Tambyah.
鈥淭he more different types of vaccine you have, the more resilience that we have to maintain vaccine supply,鈥� says at the University of Bristol, UK, who is working on the human trials of Moderna鈥檚 vaccine.
However, mRNA shots have one major drawback: they must be kept frozen at -20掳C (-4掳F) or lower, making it hard for them to reach those affected in this current outbreak, where cold storage and distribution infrastructure is limited. This means mRNA vaccines are likely to benefit high-income countries the most, while the countries worst affected will have to rely on better access to existing vaccines.
鈥淪ome countries in the West have vaccines in stock, and they should provide these to African countries and other countries that are at risk, because people have to look at this as one boat that we are all in, and if it sinks everyone will sink,鈥� says Udahemuka.
Cell
Article amended on 9 September 2024
We corrected the virus used in the JYNNEOS vaccine.
