London, Oct 14 : With Covid-19 proving the credibility of mRNA technology, many drug companies are racing to apply the same formula for developing vaccines for influenza, Nature reported. While Moderna, Pfizer and Sanofi have, in recent months, initiated Phase 1 trials of mRNA-based seasonal flu vaccine candidates, more companies intend to follow their leads next year. However, unlike Covid-19, mRNA-based flu shots could also prove a more challenging test as nine flu jabs from four different vaccine manufacturers are already available in the US alone. Although the shots built around inactivated viruses or recombinant proteins are safe, they typically offer only 40-60 per cent protection from infection. At the same time, mRNA-based jabs might produce broader immune responses, better sequence fidelity of proteins, and accurate strain selection. Moreover, the technology makes it easy to incorporate large numbers of antigens -- all of which could translate into greater immune protection, the report said. But mRNA is also prone to tolerability issues, as seen in Covid shots developed by Moderna and Pfizer -- they often cause sore arms, headaches, low-grade fevers and fatigue. These same symptoms can occur with approved flu shots, but typically are much milder in degree. On the other hand, the potential benefits of mRNA for preventing flu are many, majorly because of how it is manufactured. "Because mRNA vaccines are manufactured synthetically, by encoding a target antigen sequence into a plasmid template, they offer high fidelity: encoded antigens exactly match the flu strains selected for each year's vaccine. By contrast, inactivated virus vaccines that are made in egg- and cell-based systems often suffer from sequence mutations that weaken their effectiveness," the report said. The recombinant protein vaccines also offer that same fidelity advantage, but the manufacturing process for these is comparatively cumbersome. The flexibility and speed of mRNA vaccine production also means that drug makers could wait longer to begin manufacturing -- starting production in May, say, instead of February, for the northern hemisphere. This would enable them to make more informed decisions about what strains to include, the report said. /IANS