An English country doctor's bold use of one contagion to fight another in 1796
ushered in the modern era of immunoloqy. By then, though, the idea that something virulent could be made beneficial was not new. The painful, deadly variola virus had killed hundreds of millions, but it also revealed a fundamental insight: Pus from smallpox patients' sores could protect the uninfected.
This early version of inoculation aqainst smallpox, known as variolation, was practiced around the world for centuries. Our experience with the novel coronavirus is far shorter, and the lessons it has for us have not yet concluded.
But more than 220 years of vaccine development have led humans to the current moment. We are witnessing another historic breakthrough, this time with an entirely new method of fighting disease.
IT'S HARD TO IMAGINE places more different from one another than Delhi, India: Mexico City, Mexico; and Gary, Indiana. Yet years after I visited those cities, they' re indelibly linked in my memory for one reason: the foul, pol-
luted air smothering their landscapes.
The pollution was so heavy you could see it wafting through the interiors ofmodern buildings (Delhi, 2016), feel itstinging your eyes (Mexico City, 1972), and smell it through closed car win-
dows (Gary, the 1960s).
Despite its ubiquity, or perhaps because of it, air pollution has rarely gotten the sustained attention it deserves. That's an outrage, given that air pollution is aglobal killer, causing an astonishing seven million premature deaths every year. But it's also an oppor-
tunity, because this is an environmental problem that we actually can fix There's no better example of thatthan the experience of the United States, which last year celebrated thesoth anniversary of the Clean Air Act.
Signed by President Richard Nixon on December 31, 1970, this single statute resulted in a77 percent decrease in the nation's air pollution. It lengthened millions of American lives, saved tril-
lions of dollars, and according to theAmerican Lung Association's Paul Bill-ings, became "the most powerful public health law enacted in the 2oth century."
Those of us of a certain age can vividly recall its impact. Think of Los Angeles 50 years ago, or Pittsburgh, or so many other locales where the horizon was a haze and grime settledon your car overnight. The Clean Air Act has been "the difference maker, in Billings's words-leaving many U.S.
communities' air quality "so much better than it was, and so much better than it is in other parts of the world."still, the problem is far from solved, as pollution expert Beth Gardiner and photographer Matthieu Paley found in reporting this month's cover story. Air pollution disproportionately harms the poor and people of color who live where it's worst. And after four years of a U.S. administration that gutted regulations, the Clean Air Act "has sur-
vived, but it has been damaged,"says environmentalist Mustafa Santiago Ali.
Though there will be challenges, Ali is convinced that the time is right to build on the act's achievements. "You have a new generation that under-
stands how important it is to have clean air,"he says. "I hope we' ll come to a point in our history, sometime soon, where not only do we understand the value of (the act), but we' re willing to do the hard work of enhancing it"Thank you for reading National Geographic.