The U.S. surpassed 500,000 deaths Monday, marking the latest grim milestone in the country's battle against the COVID-19 pandemic.

Health experts anticipated reaching the current death toll this month, as cases and hospitalizations peaked last month. Even as the trend is decreasing on both fronts, with deaths likely to slow in coming weeks, variants circulating bring a new wave of concerns.

President Joe Biden held a vigil Monday evening to remember the 500,000 lives lost.

"While we have been fighting this pandemic for 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. And we must do so to honor the dead, but equally important, care for the living and those left behind," Biden said.

Projections of the circulation of the U.K. variant (B.1.1.7) show it will be the dominant strain in the U.S. by March. Studies are ongoing about the effects of the new strain, with the U.K. saying earlier this month it could be more deadly in addition to being more transmissible. But health experts believe the vaccines will continue to be effective in protecting against the strain.

Meanwhile, Johnson & Johnson (JNJ) is slated to have its vaccine candidate analyzed by independent experts for the U.S. Food and Drug Administration (FDA), with anticipation of a rollout coming as early as the weekend. The single-dose vaccine would alleviate the burden on administrators for current two-dose vaccines and could help to reach more vulnerable populations because it requires less-intense cold storage than mRNA vaccines.

Novavax (NVAX), another vaccine candidate that has commitments for its candidate in the U.S. and globally, is now fully enrolled for its Phase 3 clinical trial, with results and a filing for emergency use authorization expected by Spring.

Another candidate from GlaxoSmithKline (GSK) and Sanofi (SNY), which partnered for the effort, is moving ahead with a new formulation for Phase 2 after a previous version was deemed ineffective. The duo expects to start Phase 3 by the second quarter if all goes well.

Even as the U.S. pursues reopening on the basis of increased vaccinations and better testing, the U.K. announced it will begin reopening its economy as its speedy vaccination efforts are paying off. Prime Minister Boris Johnson announced a phased reopening that would begin in April.

FDA and variants

In new guidance Monday, the FDA addressed how to handle tweaking for variants for tests, treatments and vaccines. The question had been lingering as some vaccine companies have already announced efforts to create booster or second generation candidates to address concerning variants — such as the strain that originated in South Africa (B.1.351).

"Further discussions will be necessary to decide whether in the future, modified COVID-19 vaccines may be authorized without the need for clinical studies," the guidance said.

In a briefing Monday, FDA acting director Dr. Janet Woodcock said the agency was monitoring the variants and developing planning to respond to anything that arises.

The FDA's top vaccine expert, Dr. Peter Marks, said the immunogenicity studies, which would be required in the event of a new formula or booster shot, would only need to be tested on a couple hundred individuals — orders or magnitude smaller than the 30,000-participant clinical trials.

"This is a matter of getting prepared," Marks said. "We need to have the studies conducted to facilitate potential strain changes so that if we need to swap something we can do it in a relatively quick manner."

More from Anjalee:

• Telehealth's future depends on bridging the digital divide: Hospital CEO

• What you need to know about at-home, over-the-counter COVID-19 tests

• Biden COVID-19 adviser: Vaccine news is great, but we still have a ways to go

Read the latest financial and business news from Yahoo Finance.

Follow Yahoo Finance on Twitter, Facebook, Instagram, Flipboard, SmartNews, LinkedIn, YouTube.

Follow Anjalee on Twitter @AnjKhem.