The U.S. is entering a new phase of the Covid-19 pandemic as people settle back into normal life thanks to vaccines, but public-health authorities are preparing for Americans to live with the disease lurking in the background for the long run. Many health professionals believe that reaching herd immunity is a distant goal, due both to highly varied vaccination rates in the U.S. and uncertainty about just how much Covid-19 must be suppressed to effectively stop its spread.

Instead, they are focused on how to make it a manageable disease, with steps like close surveillance and rapid response to outbreaks in a partially vaccinated population. Calls for masks and social distancing could return, too, in efforts to control future flare-ups, health authorities say. “I think our experience historically is we will find a new normal living with this disease,” said John Brooks, chief medical officer of the Covid-19 response at the Centers for Disease Control and Prevention. “The question is, what is that new normal going to look like?”

About 44% of the U.S. population is fully vaccinated, data show, and average daily reports of new cases and deaths have fallen to the lowest levels since the pandemic was ramping up. Masks are coming off as state restrictions drop. People are crowding restaurants, airports and sports stadiums again, and vaccinations have helped protect elderly people who are the most at risk of dying from Covid-19 infections.

But Covid-19 has been suppressed, not vanquished. Epidemiologists are concerned its continued spread globally may spawn dangerous mutations.

“This particular outbreak, I think the eulogies are a bit premature,” said Jeffrey Duchin, the health officer for the public-health agency covering Seattle and King County, Wash., who believes Covid-19 could remain a part of our lives for years and even decades to come.

Low-vaccination areas in the U.S. could create pockets with elevated Covid-19 infection rates for months or years, while highly vaccinated areas may achieve a sort of local herd immunity, said Anthony Fauci, President Biden’s chief medical adviser for the pandemic. Vaccination rates are starkly different around the U.S., from Vermont, where nearly 63% of the population is fully vaccinated, to Mississippi, where the rate is about 28.5%, recent federal data show.