http://www.sciencemag.org/news/2021/08/unethical-unnecessary-covid-19-vaccine-booster-debate-intensifies

The greater infectiousness of the Delta variant of SARS-CoV-2 has scientists and governments debating whether booster shots of COVID-19 vaccines are needed in some countries given limited vaccine supplies elsewhere.

As the extraordinarily infectious Delta variant of SARS-CoV-2 continues to spread around the world, vaccines’ powers are showing their limits. Although they are still extremely effective at preventing severe COVID-19, the tantalizing hope that the shots could block almost all infections—and squelch transmission—has evaporated. That has upended return to office and school plans, threatened economic recoveries, and spurred fresh political rows over mask and vaccination mandates.