Why is it so hard to foresee what changes in the flu genes will happen next and design a vaccine accordingly? For the same reason that Bumpus needed to actually measure those sparrows. Bumpus knew that the survivors would have some traits that allowed them to withstand the cold, but many such traits exist. Neither he nor the birds could know in advance which characteristics would have been the smart ones to bear, because the variation itself is produced at random. Selection will produce better adapted individuals, but the paths to that adaptation are often innumerable.
Similarly, we know that the flu virus will change in response to selection, but the precise direction it will take is difficult to predict, because evolution itself is never goal-oriented. The sparrows weren’t trying to get to a particular point, and neither is the flu. All scientists can do is study the genetic variation that exists in the viruses from a given year, and try to determine which mutations are statistically more likely to occur the next time.
Scientists don’t fully understand why some viruses, like polio, seem to be evolutionarily conserved, as it’s termed, while others change like chameleons. But the distinction means that to conquer the flu, we need to proceed on two fronts. First, of course, broad vaccine coverage is essential: The more vaccinated people, the greater our herd immunity and the better the protection for vulnerable individuals. But second, because the flu virus is such an evolutionary quick-change artist, we need to redouble our efforts to make better vaccines. An average efficacy of 62 percent instead of, say, 90 or 95 percent, is not because the scientists developing the vaccine aren’t as clever as Jonas Salk. It’s because flu is different, evolutionarily, from polio. And that means that we can’t just concentrate on getting everyone vaccinated. We need to do more research into rapid evolution.
Indeed, a recent report from the University of Minnesota’s Center for Infectious Disease Research and Policy decried the focus on getting more widespread coverage with the currently less-than-perfect vaccines, rather than on improving the efficacy of the vaccines themselves. The lead author of the report, Dr. Michael Osterholm, said in an accompanying release, “We found a general perception that we don’t need a better flu vaccine, we just need to make more of it faster.” But the more basic research on viruses that will lead to improved vaccines is crucial, since the flu, like humanity and those sparrows, keeps on evolving.
Marlene Zuk is a professor in the department of ecology, evolution, and behavior at the University of Minnesota. Her book “Paleofantasy: What Evolution Really Tells Us about Sex, Diet, and How We Live” is forthcoming in March.