WASHINGTON — Two weeks after celebrating America's near "independence" from the coronavirus, President Joe Biden is confronting the worrying reality of rising cases and deaths — and the limitations of his ability to combat the persistent vaccine hesitance responsible for the summer backslide.

Cases of COVID-19 have tripled over the past three weeks, and hospitalizations and deaths are rising among unvaccinated people. While the rates are still sharply down from their January highs, officials are concerned by the reversing trendlines and what they consider needless illness and death. And cases are expected to continue to rise  in coming weeks. 

While the national emergency may have faded, officials say the outbreak is now a more localized crisis in communities where not enough people have rolled up their sleeves. 

"Look, the only pandemic we have is among the unvaccinated," Biden said Friday, echoing comments made earlier in the day by Dr. Rochelle Walensky, director of the Centers for Disease Control and Prevention.

The rising numbers are being driven by large pockets of infection among the more than 90 million eligible Americans who have yet to get shots. Just four states with low vaccination rates made up 40% of new cases last week, and nearly half of them came from Florida alone.

However, there is little appetite in the White House for a return to broad mandates for masks or other measures, as 161 million Americans are already fully vaccinated.

Reflecting that mindset, Walensky said Friday that in low-vaccination areas with rising cases, "local policymakers might consider whether masking at that point would be something that would be helpful for their community." 

Some communities are acting. Los Angeles County on Thursday reinstituted its requirement that masks be worn in most indoor settings regardless of vaccination status, and health officials in Las Vegas recommended on Friday that workers and patrons in the tourism hotspot wear face coverings while inside.

With three highly effective vaccines authorized for use in the U.S., the Biden administration believes the most effective way to attack the virus is not trying to slow the spread with mass masking and such — something the U.S. showed it was not very good at last year — but to continue to press the importance of vaccinations.

It's no easy fix. Many Americans remain resistant or unmotivated to get shots, despite months of often-creative efforts by federal and state officials and the private sector to spread information about vaccine safety and accessibility.

Surgeon General Vivek Murthy added that while government can play an important role, "this has got to be an 'all of the above' strategy with everybody in," including schools, employers, technology companies and individuals.

In recent days, the administration has turned its focus to younger Americans. It enlisted pop star Olivia Rodrigo for a day-long White House visit Wednesday with Biden and top infectious disease expert Dr. Anthony Fauci that was heavily documented for social media. Younger people are at lowest risk of adverse outcomes from the virus and have proven to be among the least likely to get vaccinated.

But another huge group has proven to be an even more vexing challenge: Republicans. The White House has long acknowledged that, given rampant disinformation about the vaccines and the nation's partisan divides, it would have little success convincing the GOP to get on board. Instead, administration officials have amped up criticism in recent days of public officials and social media companies for spreading or not condemning vaccine misinformation spreading among the GOP. 

"They're killing people," Biden said Friday of social media companies, speaking a day after Murthy, the surgeon general, warned that false information about vaccines spreading on platforms like Facebook posed a public health risk to the nation.

Efforts for comment from major platforms were not immediately successful.

The new government expression of frustration comes amid near disbelief that tens of millions of Americans continue to refuse to get vaccinated, needlessly extending the pandemic and costing lives, as health officials emphasize that nearly all serious cases and deaths are now preventable.

More than 99% of COVID-19 deaths and 97% of hospitalizations are among people who have not been vaccinated, according to the CDC.

The pandemic is now "one that predominantly threatens unvaccinated people," White House COVID-19 coordinator Jeff Zients said Friday. 

He said the Biden administration expects cases to increase in the weeks ahead because of spreading in communities with low vaccination rates But Zients added that there is a sign that the increased cases are driving more people in those communities to seek vaccination, reporting that "states with the highest case rates are seeing their vaccination rates go up" faster than the national average.