The Netherlands is battling two epidemics of the novel coronavirus: one against its existing variants, in which cases are declining, and "another epidemic involving the U.K. variant, in which infections are increasing," the Dutch National Institute for Public Health and the Environment said in a situation report released Tuesday.

The so-called U.K. variant, first identified in England last September, has caused a massive jump in COVID-19 hospitalizations in the United Kingdom and Ireland.

In the Netherlands, government officials said they were "gravely concerned about the U.K. variant." Over the weekend they introduced a nighttime curfew which has sparked riots.

Over the last two weeks, the Netherlands has reported an 11.7% positivity rate for COVID-19 tests.

ABC News’ Christine Theodorou contributed to this report.

The worldwide number of people who have been diagnosed with COVID-19 surpassed 100 million on Tuesday, according to real-time data collected by Johns Hopkins University. The United States accounts for over 25 million of those cases.

For perspective, only 14 countries in the world have populations over 100 million, according to the latest data from the World Bank Group.

The grim milestone comes just over one year since the first COVID-19 case was confirmed in Wuhan, China, on Dec. 31, 2019.

The number of people who have died from COVID-19 in the United Kingdom has surpassed 100,000, British Prime Minister Boris Johnson announced Tuesday.

"It's hard to compute the sorrow contained in that grim statistic," Johnson said.

More than 35,000 people in the U.K. are hospitalized with COVID-19, which is "substantially" above the peak in April, according to Johnson.

The number of people testing positive for the disease remains high but is decreasing slowly, with 20,089 new cases reported Tuesday, according to Johnson.

ABC News’ Christine Theodorou contributed to this report.

This year's Boston Marathon will be held on Oct. 11, if road races are allowed in Massachusetts' reopening plan at that time, according to the Boston Athletic Association.

A virtual race will also be offered as an option to runners.

"While it was of course the right thing to do, canceling the 2020 Boston Marathon for the first time in its 124-year history was one of the hardest announcements to make," Boston Mayor Marty Walsh said in a statement Tuesday.

"Today, I'm filled with hope, as we set our sights on October for the running of the 125th Boston Marathon," he added. "We have a ways to go before we're out of the woods, but guided by sound judgment and the advice of our public health experts, I am hopeful that we'll get to enjoy the return of one of Boston's most storied traditions this fall."

ABC News' Leo Mayorga contributed to this report.

Forty people in Gambia who tested positive for COVID-19 over the past week have refused to self-isolate or have escaped treatment centers, according to the country's health ministry, which vowed to reveal the identities of those flouting public health regulations.

Officials are also aware of a "large number of travelers who recently arrived" in the small West African nation from countries considered COVID-19 hotspots and "have refused to abide to official protocols and/or report to the health authorities for the mandatory test upon arrival," said Modou Njai, director of health promotion and education at Gambia's Ministry of Health.

"The Ministry continues to treat these matters with utmost and grave concern and thus, the Ministry is hereby giving an order and ultimatum to all those concerned, that they are required to report themselves to the health authorities with immediate effect and failure of which will lead to serious consequences, including the publication of names and identifying information of all those at large," Njai said in a statement Tuesday.

"The Ministry would like to stress that this serious and ruthless misconduct will no longer be condoned under any circumstances," he added. "Anyone found not willing to cooperate with COVID-19 regulations will have their names and identifying information published on the media and thereafter, drastic measures will be taken against anyone that is non-compliant."

Gambia, home to some 2.3 million people, has confirmed 4,008 cases of COVID-19 since the start of the pandemic, including at least 128 deaths, according to the latest data from the health ministry.