What makes it a different beast? Conventional mRNA vaccines consist of messenger RNA that carries the genetic code for covid’s spike protein. Once that mRNA enters the body, it gets translated into proteins by the same cellular machinery that translates our own messenger RNA.
Self-amplifying mRNA vaccines contain a gene that encodes the spike protein as well as viral genes that code for replicase, the enzyme that serves as a photocopier. So one self-amplifying mRNA molecule can produce many more. The idea of a vaccine that copies itself in the body might sound a little, well, unnerving. But there are a few things I should make clear. Although the genes that give these vaccines the ability to self-amplify come from viruses, they don’t encode the information needed to make the virus itself. So saRNA vaccines can’t produce new viruses. And just like mRNA, saRNA degrades quickly in the body. It lasts longer than mRNA, but it doesn’t amplify forever.
Japan approved the new vaccine, called LUNAR-COV19, in late November on the basis of results from a 16,000-person trial in Vietnam. Last month researchers published results of a head-to-head comparison between LUNAR-COV19 and Comirnaty, the mRNA vaccine from Pfizer-BioNTech. In that 800-person study, vaccinated participants received either five micrograms of LUNAR-COV19 or 30 micrograms of Comirnaty as a fourth dose booster. Reactions to both shots tended to be mild and resolve quickly. But the self-amplifying mRNA shot did elicit antibodies in a greater percentage of people than Comirnaty. And a month out, antibody levels against Omicron BA.4/5 were higher in people who received LUNAR-COV19. That could be a signal of increased durability.
The company has already filed for approval in Europe. It’s also working on a self-amplifying mRNA vaccine for flu, both seasonal and pandemic. Other companies are exploring the possibility that self-amplifying mRNA might be useful in rare genetic conditions to replace missing proteins. Arcturus, the company that co-developed LUNAR-COV19 with the global biotech CSL, is also developing self-amplifying messenger RNA to treat ornithine transcarbamylase deficiency, a rare and life-threatening genetic disease. It’s an mRNA bonanza that will hopefully lead to better vaccines and new therapies.