The influenza virus has yet to hit the Northern Hemisphere, but flu vaccine season is already in full swing, with banners outside pharmacies urging: "Get Your Flu Shot Now." What's not advertised, however, is just how lackluster the vaccine is. The most commonly used flu shots protect no more than 60% of people who receive them; some years, effectiveness plunges to as low as 10%. Given that a bad flu season can kill 50,000 people in the United States alone, "10% to 60% protection is better than nothing," says Michael Osterholm, an epidemiologist at the University of Minnesota in Minneapolis. "But it's a terribly inadequate vaccine for a serious public health threat." Now, researchers are striving to understand why it fails so often—and how to make a markedly better one.
They're questioning what was once received wisdom: that the vaccine fails when manufacturers, working months ahead of flu season, incorrectly guess which strains will end up spreading. And they're learning instead that the vaccine may falter even when the right strains were used to make it, perhaps because of how it is produced or quirks of individual immune systems. "It's much more complicated than we thought," Osterholm says. "I know less about influenza today than I did 10 years ago."
The influenza vaccine teaches the body to produce antibodies against the head of the virus's surface protein, hemagglutinin (HA). Those antibodies ideally prevent HA from attaching to cellular receptors, thwarting infection. But HA's head is highly mutable, which is why vaccine makers must come up with a new formula every year.