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.

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).

But 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. It followed six straight days of more than 1,000 new COVID-19 cases in the county, with nearly 400 people hospitalized with COVID-19 as of Wednesday, up 275 from the week before.

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.

Overseas, COVID-19 restrictions are being reimposed in countries experiencing worrying spikes. The Netherlands announced it was re-imposing work-from-home guidelines due to soaring COVID-19 infections, just weeks after lifting them, as well as some restrictions on bars, restaurants and nightclubs.

Britain ended over a year of COVID-19 lockdown restrictions on Monday but the so-called “Freedom Day” was marred by surging infections and grim forecasts.

The U.S. Centers for Disease Control and Prevention on Monday issued a more severe warning against travel to the United Kingdom, elevating the nation to “Level Four: COVID-19 Very High,” the CDC’s highest level.

(Reporting by Maria Caspani in New York; Additional reporting by Anurag Maan, Sharon Bernstein and Caroline Humer; Editing by Howard Goller)