http://www.sciencemag.org/news/2021/08/do-delta-breakthroughs-really-mean-vaccine-protection-waning-and-are-boosters-answer

Israel has started to administer COVID-19 booster shots to people ages 40 and older. 

Even as the United States made the controversial announcement this week that it would begin to offer COVID-19 vaccine booster shots in September, scientists and public officials were scrambling to assess the rationale officials offered: that the vaccines’ protection against the Delta variant of SARS-CoV-2 is waning.