Israel has among the world's highest levels of vaccination for COVID-19, with 78% of those 12 and older fully vaccinated. Yet the country is now logging one of the world's highest infection rates, with nearly 650 new cases daily per million people. More than half are in fully vaccinated people. The effects of waning immunity may be beginning to show. A preprint published last month by physician Tal Patalon and colleagues ... found that protection from COVID-19 infection during June and July dropped in proportion to the length of time since an individual was vaccinated. People vaccinated in January had a 2.26 times greater risk for a breakthrough infection than those vaccinated in April. At the same time, cases in the country, which were scarcely registering at the start of summer, have been doubling every week to 10 days since then, with the Delta variant responsible for most of them. What is clear is that "breakthrough" cases are not the rare events the term implies. As of 15 August, 514 Israelis were hospitalized with severe or critical COVID-19, a 31% increase from just 4 days earlier. Of the 514, 59% were fully vaccinated. To try to tame the surge, Israel has turned to booster shots. As of Monday, nearly 1 million Israelis had received a third dose. Yet boosters are unlikely to tame a Delta surge on their own, says Dvir Aran, a biomedical data scientist at Technion. Aran's message for the United States and other wealthier nations considering boosters is stark: "Do not think that the boosters are the solution."