After weeks of declines and then a plateau, the average number of new Covid-19 cases saw a 7% increase from the previous week, Centers for Disease Control and Prevention Director Dr. Rochelle Walensky said on Friday. The average of new virus-related hospitalizations also saw a slight increase from the previous week, she said.
More than two dozen states are reporting at least a 10% increase of new cases compared to the previous week, according to data from Johns Hopkins University.
"People over 65, a large proportion of them, have been vaccinated, are protected. That's one of the reasons we have not seen a huge spike in hospitalizations," Dr. Ashish Jha, dean of the Brown University School of Public Health, told CNN on Sunday. "A lot of the spread is happening among younger people ... that's the group that is moving around, kind of relaxing, getting infected."
Fueling the rise of cases is a highly contagious -- and potentially more deadly -- variant of the virus. The B.1.1.7 variant, first spotted in the UK, has now been identified in 51 US jurisdictions, according to the CDC, and is projected to become the dominant variant in the country by the end of March or early April.
But that's not all that's helping drive case increases, experts say.
Spring break crowds swelled in popular beach destinations, including South Florida, where local leaders said the vacationers were more than they could handle. And air travel has broken pandemic records this month, with millions of Americans boarding planes.
"We're weeks away from a point where we can begin to do these things a bit more safely, but I think states have just moved too fast," Jha said.
So far, about 28.2% of the US population has received at least one dose of a Covid-19 vaccine, according to CDC data, and 15.5% of Americans are fully vaccinated.
State leaders sound alarm
State leaders across the US have expressed concern about their latest Covid-19 data, urging residents to double down on safety measures just a few weeks longer until enough of the population is protected against the virus.
Michigan is in the middle of another Covid-19 surge, a top health official in the state told CNN on Sunday.
And cases are increasing most in younger people, specifically the 10 to 19-year-old age group, Dr. Joneigh Khaldun, Michigan's chief medical executive, said.
The state is experiencing community spread, Khaldun said and attributed the rise in cases to a number of factors, like more gatherings and more mobility, economic reopenings and specific outbreaks in some prisons and schools.
In Illinois, state officials announced Friday they were deploying rapid response vaccination teams to several counties and expanding vaccine eligibility in response to a "concerning possible trend in increasing COVID hospitalizations and case rates."
"Recent increases in hospital admissions and test positivity are concerning new developments and we don't want to go down the same path we've seen before and experience a resurgence in the pandemic," Dr. Ngozi Ezike, director of the Illinois Department of Public Health, said in a statement.
"We cannot move forward if our metrics are going backward," the director added.
Also on Friday, Vermont officials reported the state's highest single-day case total since the pandemic's start, with more than 250 new reported infections.
The increase is likely fueled by more people moving around now that warmer weather is here and by variants that are circulating, Dr. Mark Levine, the state's health commissioner, said.
"Our efforts to vaccinate Vermonters is a race against what the virus does best: move easily from person to person," Levine said. "Throughout the country, including up and down the Eastern Seaboard, case numbers are up."
New Hampshire officials reported late last week an increase in the average number of daily new Covid-19 cases and the state's test positivity rate. And the number of infections among people under 60 years old is also increasing -- especially in teenagers and people in their 20s, officials said.
The rise in cases will likely continue for a couple of weeks, Gov. Chris Sununu said, adding the state is likely seeing a "spring surge."
In Pennsylvania, the governor said last week that the number of new cases and the statewide percent positivity slightly increased, calling the upticks "concerning."
"As more and more Pennsylvanians are getting vaccinated, we must not forget to follow the mitigation measures still in place," Gov. Tom Wolf said in a statement. "As the weather gets warm, please remember to wear a mask, practice social distance and wash your hands frequently as the virus still has a presence in our communities."