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A new vaccine strategy could make flu shots cheaper, safer, and easier to produce. Using synthetic messenger RNA (mRNA) instead of proteins purified from viruses, German scientists have shown they can protect mice, ferrets, and pigs against influenza. “This is a very interesting new approach,” says Hans-Dieter Klenk, a virologist at the University of Marburg in Germany who was not involved in the work. Now, most flu vaccines consist of hemagglutinin and neuraminidase, the two proteins covering the surface of the virus. To produce these molecules, the three predominant influenza strains are cultured in fertilized chicken eggs or, increasingly, in cell culture. Virus is then harvested and broken up so that the two proteins can be purified.
How well a given strain grows in either eggs or cells is hard to predict, however, and producing enough virus for millions of vaccine doses takes many months every year. This is a particular problem when a new pandemic influenza strain emerges, as happened in 2009 with swine flu. Most of the vaccine against that virus became available well after the pandemic was past its peak.
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