(Adds American Academy of Pediatrics guidance for schools, Indiana University ruling)
By Maria Caspani
NEW YORK (Reuters) - A rapid increase in coronavirus cases in the United States and abroad is fueling fears of a pandemic resurgence and sending shockwaves through the stock market as the highly contagious Delta variant takes hold and vaccinations lag in several states.
Largely due to outbreaks in parts of the country with low vaccination rates, the number of new cases, hospitalizations and deaths due to COVID-19 have been on the rise in recent weeks.
The vaccines work against the Delta variant, but lab tests have shown them to be less effective than they were against the original form of coronavirus.
Studies have also shown that two shots of the Pfizer/BioNTech vaccine and of the AstraZeneca vaccine are much more effective than one shot against being infected with the virus, making it more important for people to be fully vaccinated.
Concerns the outbreaks could derail an economic recovery sent the Dow down more than 2% on Monday.
In a speech about the U.S. economy, President Joe Biden said the recovery hinges on getting the pandemic under control. He said four states with low vaccination rates accounted for 40% of all cases last week.
"So please, please get vaccinated," Biden said. "Get vaccinated now."
The average number of new COVID-19 cases per day has tripled in the past 30 days in the United States, according to an analysis of Reuters data. In the month from June 18 to Sunday, it climbed from 12,004 to 32,136.
The average number of people hospitalized with COVID-19 has gone up 21% over the past 30 days to over 19,000, up from 16,000, according to the same Reuters analysis.
Deaths, which can lag weeks behind a rise in cases, rose 25% last week from the previous seven days with an average of 250 people dying a day.
DELTA VARIANT CHALLENGES
Some states have been especially hard hit. All but two of the 75 Arkansas counties have substantial or high levels of transmission, according to data from the U.S. Centers for Disease Control and Prevention (CDC).
The Delta variant is responsible for 90% of current new cases in Utah's Salt Lake County, according to epidemiology manager Ilene Risk.
To combat the rising infections, the county has enlisted faith leaders and doctors to persuade the roughly 40% of eligible people who are not fully vaccinated to accept the shots, she said.
Even in states with higher vaccination rates, such as New York, officials have expressed concern about fresh outbreaks, pointing to the significantly more contagious Delta variant.
So far, the variant has been detected around 100 countries globally and is now the dominant variant worldwide, top U.S. infectious disease expert Anthony Fauci told reporters last week.
In California, Los Angeles County reimposed a mask mandate at the weekend following a surge in cases.
While New York City Mayor Bill de Blasio acknowledged a rise in the number of cases, he told a daily news conference on Monday there were no plans to reintroduce mask mandates. He vowed instead to redouble vaccination efforts.
The American Academy of Pediatrics on Monday released updated recommendations for schools that included mask-wearing for everyone over the age of 2, regardless of vaccination status.
Earlier this month, the CDC had updated its own guidance for schools in an effort to help reopen in the fall, recommending masks indoors for everyone not fully vaccinated, among other guidelines.
A large number of U.S. colleges require students to get the shots to return to campus, but some mandates have faced opposition.
In one of the first rulings of its kind, a federal judge on Monday said students at Indiana University must comply with the school's inoculation requirement for the fall semester.
U.S. District Court Judge Damon Leichty in South Bend, Indiana, rejected the argument by eight students that the school violated their rights.
"This university policy isn't forced vaccination," wrote the judge. "The students have options -- taking the vaccine, applying for a religious exemption, applying for a medical exemption, applying for a medical deferral, taking a semester off, or attending another university."