STAT In the spring of 2009, the first flu pandemic in four decades began. Caused by an H1N1 virus that emerged from pigs, likely in Mexico, it spread quickly around the globe.
The world got lucky in 2009. Doubly so. The “swine flu” virus was distinct enough from previous H1N1 viruses that it could cause a pandemic, but it had enough genetic similarities to viruses that had circulated for decades that many people had some immune defenses, which blunted its severity.
The other truly lucky break was that multiple flu vaccines targeting H1N1 were already licensed in the U.S., so the Food and Drug Administration could fast-track approval of pandemic vaccines. That tool, used regularly when seasonal flu shots require updating, sidestepped the need to run a series of clinical trials that could have added as much as a year to the race to get vaccines into arms.