US may soon reach a tipping point on Covid-19 vaccine demand. Here’s why that’s concerning As US health officials race to get more Covid-19 shots into arms to control the virus, experts now warn the country will run into another challenge in the next few weeks: vaccine supply will likely outstrip demand. “While timing may differ by state, we estimate that across the U.S. as a whole we will likely reach a tipping point on vaccine enthusiasm in the next 2 to 4 weeks,” the Kaiser Family Foundation said in a new report published Tuesday. “Once this happens, efforts to encourage vaccination will become much harder, presenting a challenge to reaching the levels of herd immunity that are expected to be needed.”