UGH: Measles is an early warning sign for outbreaks of more serious diseases. “Once you have less than 95 percent of the population immune, you have enough people to keep the disease in circulation, Kretsinger explains. Most countries simply never attained that herd immunity level. Even if you maintained at 92 percent every year, as the population overall increases you’re increasingly likely to see an outbreak. . . . Even if there weren’t an increasing pushback from vaccine-hesitant parents, the truth is that over the last nine years our global vaccination rates have flatlined for pretty much all vaccines. Vaccination rates haven’t been decreasing over that time, Kretsinger says, it’s just that we never really achieved the level we needed to.”

Plus: “Should those diseases come back, we may be worse prepared in some ways than before. For a long time, the older generations in our society grew up in the pre-vaccine era, which meant that the overwhelming majority of them were exposed to these viruses. Now we have much less circulation of viruses, but also not sufficiently high vaccine coverage to prevent transmission altogether, and the combination is worrisome.”