WASHINGTON - By the light of 500 candles as "Amazing Grace" played outside the White House, President Joe Biden bowed his head in a minute of reflection on the 500,000 American lives lost to the coronavirus, crossing himself after the music faded out. 

Moments earlier, the president noted that the U.S. death toll from the pandemic has exceeded both world wars and the Vietnam War combined.

"The people we lost were extraordinary," Biden said in the White House's Cross Hall. "They span generations. Born in America, immigrated to America. But just like that, so many of them took their final breath alone in America."

Somber reminders will endure for the rest of the week, with flags flying at half-staff at all federal buildings, parks and other properties.

Although it was not reflected in the solemn sundown ceremony, Monday also brought decidedly good news on the coronavirus front. The pace of vaccinations is accelerating, deaths and new infections are sharply down, and worries about just how bad the pandemic can get are being replaced with halting questions about when, exactly, all this will be behind us.

But those positive signs have been played down by a federal government that opted this week to focus on the grim pandemic milestone and is cautious of giving Americans an excuse to lower their guards prematurely. From top to bottom, the Biden administration has been less than exuberant about some of the most positive news on the pandemic front since Biden was inaugurated a month ago.

The stance reflects the classic political view that it is risky to tout good news before the battle is won, and a recognition that the trends could still be reversed.

Government experts worry that if they are too ebullient about the positive strides, it will prompt pandemic-weary Americans to relax too soon, becoming less mindful of their masks and the social distancing that remain the strongest weapons against the virus.

An uptick in gatherings or maskless moments could erase the gains the nation has made and seed new infections, experts warn. Adding to the risk is the presence of coronavirus variants that can be both more contagious and less affected by existing vaccines.

"Now we peaked, we turned around and we're coming down," Anthony Fauci, the nation's top infectious-disease expert, said in an interview. "But we're still at a weekly average of 68,000 infections. Now is not the time to say, 'We're doing really well, let's pull back.' "

The muted mood presents a contrast with the approach taken by President Donald Trump, who saw himself as booster-in-chief in touting any progress against the virus and spoke openly of his role in promoting positive news about it. Sometimes his pronouncements were not borne out by the facts, especially in highlighting what he said were promising treatments.

The Biden team's caution was reflected in the quiet tones of Andy Slavitt, a senior White House COVID-19 adviser who started and ended Moday's White House briefing on the coronavirus on a solemn note, speaking of the tragic milestone of a half-million deaths and reminding people to tune in to Biden's sundown memorial ceremony.

But between the somber bookends, officials provided some of the most unreservedly good news the nation had received in nearly a year of pandemic-induced isolation.

The seven-day average number of cases is down 75% from the peak on Jan. 11, the coronavirus task force reported. The daily hospital admission rate dropped 60% since its peak on Jan. 9. Deaths have dropped nearly 39%.

There was even more good news when it came to reopening schools, which has been a contentious issue since Biden said he wanted them to be open in his first 100 days.

Rochelle Walensky, director of the Centers for Disease Control and Prevention, said that since the CDC issued its guidance on school reopening about two weeks ago, the number of counties with coronavirus transmission in the "red" zone - enduring the highest transmission rates - has dropped from 90% to 60%.

About 18% of counties have low to moderate transmission, she said, and those counties could have full-time in-person schooling for students in kindergarten through 12th grade, she said. An additional 22% were in "substantial" range and should have a hybrid model up to fifth grade.

Walensky, too, tried to temper the good news, making it clear that the nation is hardly out of the woods.

At the daily White House news briefing, spokeswoman Jen Psaki also made it clear that Biden on Monday would not focus on the positive news in the coronavirus fight, given the sad landmark being observed.

"He is also quite mindful that tonight is not the night to give advice to the public or give an update on progress being made," Psaki said, adding that the White House was still encouraging Americans to take common-sense protective measures that most can now recite by heart.

From the beginning, Biden and his administration have sought to temper expectations. On the first full day of his presidency, Biden warned that the pandemic would get worse before it got better, adding that a wartime footing was needed to defeat the virus.

Although the federal government has secured enough vaccine to vaccinate every American by July, Biden has said it could be Christmas before things begin to feel like normal. Fauci has warned that Americans could still be wearing masks in 2022.

While tempering expectations can be a political reflex, the events of the past few days also show how easily the positive trend can be reversed.

An ice storm, and ensuing power outages, halted vaccine distribution in Texas and surrounding states last week.

Officials at the Federal Emergency Management Agency say they have prioritized vaccination sites in their recovery efforts from the storm. But Texas officials say they are worried that shuttered vaccination centers, a lack of running water caused by electricity outages, and neighbors huddled together in warming centers could seed new infections, derailing the progress they've made.

Biden administration officials also say it may be a struggle persuading some vulnerable groups to get a coronavirus vaccine. Minority populations have been hit harder by the virus - Black Americans are more than twice as likely to die of it - and there are signs that they are also more hesitant to take the vaccine, in part due to centuries of medical malpractice at the expense of Black bodies.

That means that even if vaccines are produced in sufficient numbers and distributed effectively to needy areas, it still could take a while for the population to be vaccinated in great enough share to achieve herd immunity.

And while the numbers of coronavirus deaths and infections have dropped, they are still not at the point where society can safely reopen. The CDC's guidance on mask-wearing and social distancing remains unchanged, and the agency still warns on its website: "Cases are extremely high. Avoid travel."

The pandemic has cost more American lives than both world wars and the Vietnam War combined, Biden said Monday night. And its infectious nature added a particularly painful side effect, he added: It has stopped Americans from engaging in the common rituals of mourning that honor the dead and help survivors share their sorrow.

"That's what has been so cruel," said Biden, who has suffered his own share of personal tragedy and put compassion at the heart of his political identity. "So many of the rituals that help us cope, that help us honor those we love, haven't been available to us."

He said he hoped Monday's moment would give at least a semblance of solace.

"We have to resist becoming numb to the sorrow," Biden said. "We have to resist seeing each life as a statistic or a blurb on the news."