Researchers at Rutgers University in the United States and Japanese institutions reported a needle-free mRNA vaccine approach that protected mice against SARS-CoV-2 and influenza A virus after three doses. The method used a high-pressure liquid jet to push naked mRNA into the skin, paired with two adjuvants meant to strengthen the immune response.
The result matters because earlier needle-free mRNA delivery had produced only a weak immune response. In this study, a combination of aluminum phosphate and short CpG DNA molecules lifted both antibody production and the cellular immune response, while using the adjuvants separately did not do the job and some combinations even dulled part of the response.
That improvement showed up in hard numbers. After three vaccine doses, infectious virus in lung samples from mice later exposed to SARS-CoV-2 or influenza A virus fell below the detection limit. In the COVID experiment, viral RNA in the lungs was about 24 times lower than in mice that got vaccination without adjuvants, and all of the influenza-vaccinated mice survived.
The work also points to why the skin was used. The researchers linked the stronger immune response to signals activated in the skin and nearby lymph nodes, an area rich in immune cells that can help turn a local dose into a broader defense. The approach also caused less local and systemic inflammation than laboratory mRNA vaccines based on lipid particles, which is one reason the needle-free route is drawing attention as mRNA shots become more common in flu work and other vaccine development.
But the study stops well short of a human test. The authors said the method still needs to be tried in larger animals, and appropriate doses must be determined before any possible clinical trials involving people. That leaves the core finding intact and the next step unresolved: the vaccine signal is stronger, but the dose and the animal model still have to be settled before the idea can move beyond mice.
