In the past, lulls in the pandemic were short-lived, giving way to the surge across the Sun Belt last summer, and the painful outbreak that stretched across the United States this winter.
But now, there is one crucial difference: More than half of American adults — 148 million people — have received at least one dose of a coronavirus vaccine, perhaps the biggest reason experts are optimistic that the improved outlook may last. Cases, hospitalizations and deaths have also fallen at a time when the weather is getting warmer, which, in many places, will allow people to spend more time outdoors, where the virus spreads less easily.
The situation in the United States stands in stark contrast to other parts of the world, where many countries are still scrambling to secure access to vaccines. India remains in dire crisis, and thousands of people are dying each day in Brazil.
In the United States, even as a sense of hope spreads, there remain strong reasons for caution. The pace of vaccinations is slowing, and experts now believe that herd immunity in the United States may not be attainable. More transmissible variants of the virus are also spreading, threatening to undermine the progress from vaccinations.
That could leave the coronavirus infecting tens of thousands of Americans and killing hundreds more each day for some time. A modeling study released by the Centers for Disease Control and Prevention on Wednesday, citing relaxed restrictions and a new, contagious variant, suggested that cases could tick upward again in the coming weeks, before a sharp drop-off by July. Dr. Rochelle Walensky, the director of the C.D.C., said, “We are not out of the woods yet, but we could be very close.”
Dr. Osterholm pointed to recent outbreaks in Minnesota, Michigan and Oregon as clues to how the pandemic might progress in the coming months. In pockets across the country, small outbreaks have continued to cause alarm. Infections are rising in places like Multnomah County, Ore., which contains Portland; Pueblo County, Colo.; Grand County, Utah; and Powell County, Ky.
“What we’re going to see are more of these localized outbreaks that are going to require a response from governors and mayors,” he said.
