Some 85 percent of Portugal's population is fully vaccinated. Portugal's feat has turned the country into a cutting-edge pandemic laboratory a place where otherwise-hypothetical questions about the coronavirus endgame can begin to play out. Chief among them is how fully a nation can bring the virus under control when vaccination rates are about as high as they can go. Portugal's experience is ... providing a note of caution: a reminder that 1½ years into this pandemic, the current tools of science still might not be enough. Herd immunity remains elusive. "We have achieved a good result, but it's not the solution or miracle one would think," Portugal's health minister, Marta Temido, said in an interview. In Portugal, seniors are vaccinated at a level verging on the statistically impossible: Official data puts the rate at 100 percent. But many were also vaccinated more than half a year ago " and studies from around the world, from the United States to Israel, have warned of a drop in protection by that point. One of the biggest warnings of all has come from a science institute in Lisbon, where researchers have been measuring antibody levels in several thousand people " including about 500 in Portuguese nursing homes. Shortly after those nursing home residents were vaccinated, all with the vaccine from Pfizer-BioNTech, 95 percent developed antibodies, the researchers found. But this summer ... more than one-third of the residents had lost antibodies entirely.