The search for a universal flu vaccine has focused on the stem of the lollipop-shaped hemagglutinin of the influenza virus. While the composition of the head changes, the stem is fairly constant from strain to strain. New data shows the body takes advantage of this fact too.
Researchers writing in Science Translational Medicine tracked 40 people aged 35 to 70 over a 20-year period to see how the immune system changes over a lifetime of exposure to flu viruses. Blood samples showed people exposed to the 1957 H2N2 and 1977 H1N1 pandemic strains had 3.8 times more broadly neutralizing antibodies than those who only encountered H1N1. These immune proteins target the stem of the virus, which is what researchers look for in a universal flu vaccine candidate.
"If we mimic the natural situation that occurs when a pandemic strikes using a vaccine approach, then we may be able to generate a universal flu vaccine," Mount Sinai School of Medicine postdoctoral fellow and co-author of the paper Matthew Miller told LiveScience. The heads of seasonal flu hemagglutinins are fairly consistent from year-to-year, and as such the immune response targets this area. Pandemic viruses, in contrast, have heads that are nothing like the immune system has seen before, so it creates broadly neutralizing antibodies to target the familiar part--the stem.
As the H2N2 pandemic happened more than 50 years ago, the higher antibody levels suggest exposure to viruses with highly-unusual heads causes a long-term rise in numbers of broadly neutralizing antibodies. In the context of a universal flu vaccine, this means long-lasting immunity may be achievable. Various approaches have shown promise in preclinical tests, but it will likely take years to bring a universal flu vaccine to market. In February, an FDA official said it will be at least 5 to 10 years before a vaccine is available.
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