In the public imagination, the arrival of a coronavirus vaccine looms large: It’s the neat Hollywood ending to the grim and agonizing uncertainty of everyday life in a pandemic. But public health experts are discussing among themselves a new worry: that hopes for a vaccine may be soaring too high. The confident depiction by politicians and companies that a vaccine is imminent and inevitable may give people unrealistic beliefs about how soon the world can return to normal — and even spark resistance to simple strategies that can tamp down transmission and save lives in the short term.

Two coronavirus vaccines entered the final stages of human testing last week, a scientific speed record that prompted top government health officials to utter words such as “historic” and “astounding.” Pharmaceutical executives predicted to Congress in July that vaccines might be available as soon as October, or before the end of the year.

“It seems, to me, unlikely that a vaccine is an off-switch or a reset button where we will go back to pre-pandemic times,” said Yonatan Grad, an assistant professor of infectious diseases and immunology at the Harvard T.H. Chan School of Public Health.

Or, as Columbia University virologist Angela Rasmussen puts it, “It’s not like we’re going to land in Oz.”

The declaration that a vaccine has been shown safe and effective will be a beginning, not the end. Deploying the vaccine to people in the United States and around the world will test and strain distribution networks, the supply chain, public trust and global cooperation. It will take months or, more likely, years to reach enough people to make the world safe.