Washington, D.C. Mayor Muriel Bowser announced her sister died due to complications related to COVID-19 on Wednesday at the age of 64.

In a Twitter thread, Bowser called her sister Mercia Bowser a "loving, daughter, sister, aunt, and friend" who worked "tirelessly for children, the elderly, and those with behavioral disorders until her retirement and beyond."

"We’re grateful to the doctors and nurses at Washington Hospital Center, who heroically treated her for COVID-19 related pneumonia. We thank you for your kindness and will share how our family will honor Mercia, my only sister and oldest sibling, and her beautiful spirit in the coming days," Bowser wrote.

"I ask that you continue to keep those who have been lost or impacted by the pandemic and those who are working so hard to protect us from it in your thoughts/prayers, and I respectfully request that my family and I are granted the time and space we need to mourn the loss of Mercia," she added.

My family and I are mourning the loss of my sister, Mercia Bowser, who passed away this morning due to complications related to COVID-19. Mercia was loved immensely and will be missed greatly, as she joins the legion of angels who have gone home too soon due to the pandemic.

— Muriel Bowser (@MurielBowser) February 24, 2021

Washington, D.C. recently reached more than 1,000 COVID-19 deaths, according to NBC Washington, and the country surpassed 500,000 deaths since last February.

President Joe Biden held a ceremony at the White House on Tuesday to mark the grim milestone, imploring Americans to remember the lives lost.

"That's how you heal — you have to remember. And it's also important to do that as a nation. Those who have lost loved ones, here's what I know: They're never truly gone. They'll always be part of your heart. I know what it's like to not be there when it happens. I know what it's like when you are there, holding their hands, looking into their eyes as they slip away. That movie theater where you met. The morning coffee you shared together," Biden said.

“As a nation, we can't accept such a cruel fate. We have been fighting the pandemic so long, we have to resist becoming numb to the sorrow. We have to resist viewing each life as a statistic or a blur or on the news,” he added.

Flags will be flown at half-staff over the next five days in honor of the 500,000 that have passed during the coronavirus pandemic.

According to Politico, Biden's administration has picked up the pace of vaccinations, with more than 64.2 million doses being given out as of Monday. Only about 16 million people had been given doses when Biden first took office in January.

The number of cases, hospitalizations and deaths have fallen significantly since peaks in January related to the Christmas and Thanksgiving holidays. But the U.S. still leads the world by far in the number of people dying each day.

After the first confirmed cases in February 2020, it took another four months for the country to reach 100,000 deaths from COVID-19. By December, the country had 300,000 deaths, the Associated Press reported.

According to the COVID Tracking Project, 2,196 people died on Tuesday from COVID-19 and there were 68,000 new cases, far outpacing any other country.

“It’s nothing like we have ever been through in the last 102 years, since the 1918 influenza pandemic,” Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases (NIAID) and chief medical adviser to Biden, said on CNN’s State of the Union.

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