The limited vaccine supply has curbed the Biden administration’s early ambitions for a national effort to build enthusiasm for shots that can help smother the pandemic. Much of an envisioned $1 billion public awareness campaign remains on hold, with health officials figuring it makes little sense to make their pitch when so few Americans can get vaccinated. The U.S. is not expected to make vaccines widely available to the public until the spring.

“We have to have product available before we go out and encourage people to seek it,” said Mark Weber, the federal health official charged with crafting the government’s Covid-19 advertising campaign. “We’re not there yet.”

Even as the U.S. struggles to keep up with early demand for the shots, the White House believes a messaging blitz is necessary to overcome significant amounts of vaccine hesitancy — enough to potentially prevent the country from quickly reaching herd immunity.