Plummeting vaccination rates have turned what officials hoped would be the “last mile” of the coronavirus immunization campaign into a marathon, threatening President Biden’s goal of getting shots to at least 70 percent of adults by July 4.

The United States is averaging fewer than 1 million shots per day, a decline of more than two-thirds from the peak of 3.4 million in April, according to The Washington Post’s seven-day analysis, even though all adults and children over age 12 are now eligible.

Small armies of health workers and volunteers often outnumber the people showing up to get shots at clinics around the country, from a drive-through site in Chattanooga, Tenn., to a gymnasium in Provo, Utah, or a park in Raleigh, N.C. The slowdown is national — with every state down at least two-thirds from its peak — and particularly felt across the South and Midwest. Twelve states, including Utah, Oklahoma, Montana, the Dakotas and West Virginia, have seen vaccinations fall below 15 daily shots per 10,000 residents; Alabama had just four people per 10,000 residents get vaccinated last week.

The rest are lagging behind. Tennessee and five other states are at 50 percent or below and vaccinating at such low rates that meeting the president’s threshold is very unlikely.

The steep decline began in mid-April, coinciding with federal officials’ temporary suspension of the Johnson & Johnson vaccine while they probed rare blood-clotting reactions. That slowdown has continued, with only 2.4 million adults getting their first shot last week. Officials must get a first dose to 4.2 million adults per week to meet Biden’s goal of ensuring that 70 percent of adults are at least partially vaccinated by Independence Day.