In Mississippi, where just 34 percent of the population is fully vaccinated, cases, outbreaks and hospitalizations are all on the rise. Officials there have recommended that older adults and those with chronic medical conditions avoid large indoor gatherings through July 26. “We did predict a few weeks ago that the Delta variant would be the predominant strain circulating in the state of Mississippi,” Dr. Thomas Dobbs, the state health officer, said at a news conference last week. “Unfortunately, those predictions are becoming reality, and we’re starting to pay the price for it,” he said, pointing to outbreaks among youth from summer gatherings and among older populations in nursing homes. He added: “Our collective undervaccination in the state has put us all at risk, especially the most vulnerable.”