It's been a turbulent year for the NFL. Ratings plummeted 12 percent in the regular season, even more during the playoffs. It's hard to know what hurt the league more, its public feuding with the White House over players protesting police brutality during the national anthem or the fact that people don't watch TV anymore. But it's not hard to know what's hurting the league's players: This season, the NFL reported 281 concussions, the most since the league began sharing that data in 2012.

As the nation tunes in to Super Bowl LII on Sunday, the link between repeated blows to the head and the neurodegeneration of chronic traumatic encephalopathy, or CTE, has never been stronger. Strong enough that the NFL has agreed to an estimated $1 billion class-action lawsuit brought by some 18,000 retired players. Strong enough that John Urschel, an offensive lineman for the Baltimore Ravens, retired this past July at the age of 26. His decision came two days after doctors at the University of Boston released a study of 111 brains of former NFL players, in which all but one of them showed signs of CTE. Most were linemen. Urschel, who is pursuing a doctorate in math at MIT, did the calculus and hung up his cleats.

Although it's been 90 years since CTE was first described—in boxers, as "punch drunk syndrome"—the mechanisms of the disease are still poorly understood. Scientists believe that repeated brain trauma triggers the buildup of a neurotoxic protein called tau. But why that results in symptoms of confusion, memory loss, and enhanced aggression is still largely a mystery. Currently, CTE can only be diagnosed through autopsy, and there is no treatment.

But one young biotech company believes there might, one day, be a way to prevent it.

United Neuroscience, a three-year-old spinout of veteran vaccine-maker United Bioscience, announced this week it's developing a drug designed to inoculate the brain against CTE. Traditional vaccines work by introducing a weakened version of a virus, or just a little piece of it, and training the body's immune system to recognize and assail it. Doing that for a protein you yourself make, like tau, is much trickier. Millions of years of evolution have fashioned the human body into a hardline xenophobe; foreigners bad, me good.