Rates of Covid-19 cases, deaths, and hospitalizations in America have hit their lowest levels in nearly a year and are still falling fast. But experts warn it's still too early to declare victory against the coronavirus.

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America is hitting milestones in the fight against Covid-19

According to the Washington Post, as of Sunday, average daily Covid-19 deaths had fallen below 580 deaths per day, a rate that was last achieved for 17 days in June and July of 2020.

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Meanwhile, average daily Covid-19 hospitalizations have dropped to 10 per 100,000 people, with three per 100,000 people arriving in the ICU with Covid-19. And average daily Covid-19 cases have dropped to fewer than 35,000, the Post reports.

At the state level, Texas reported zero Covid-19 deaths for the first time since March 2020, Maryland reported its lowest number of new daily Covid-19 cases since March 2020, and Virginia saw its lowest rate of new cases since the beginning of the pandemic, Axios' "Vitals" reports.

Meanwhile, Arizona, Massachusetts, and Minnesota all reported zero Covid-19 deaths in a day for the first time in months, Axios reports.

As for vaccinations, 59.8% of American adults have received at least one shot of a vaccine, while 47.4% have completed all required doses of a vaccine, according to CDC. In addition, 84.6% of Americans at least 65 years old have received at least one shot, and 72.8% have completed all required doses.

The vaccines are proving highly effective at preventing hospitalizations in the real world. According to data from Cleveland Clinic, more than 99% of patients hospitalized at its facilities with Covid-19 are not fully vaccinated.

"We are doing extremely well in the U.S. and are well on our way of moving past the pandemic," Monica Gandhi, professor of medicine at the University of California-San Francisco, said.

3 big reasons why experts say there's still cause for concern

But even as experts were encouraged by America's progress in its Covid-19 fight, several cited three key causes for concern: a decline in new vaccination rates, the continued emergence of new variants, and an increase in the share of Covid-19 hospitalizations occurring among young people.

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"I do think we are moving in the right direction … but there are also some worrying signs ahead," Carlos del Rio, a professor of medicine at Emory University, said.

According to the latest data, vaccination rates have dropped by 3% compared with last week, with fewer than two million Americans getting vaccinated each day, the Post reports.

Jesse Goodman, a professor of medicine and infectious diseases at Georgetown University, said given the declining vaccination rates and the increased spread of the coronavirus variant first found in India, it "would be highly premature to declare victory even in the U.S."

"We remain in a race between vaccines and the variants, so we need to continue to overcome hesitancy and ramp up vaccination rates here and, at least as important, do much better to get vaccines produced and distributed worldwide," he said.

A further trend worrying experts is the increase in the share of Covid-19 hospitalizations occurring among young people. According to COVID-Net, a surveillance system from CDC, people aged 18 to 49 made up just 20.5% of Covid-19 hospitalizations at the start of 2021. Now, they make up 36%.

Experts say the trend likely is due to low vaccination rates among younger people, many of whom perceive themselves as being at minimal risk from Covid-19 but can still suffer serious complications or death.

President Joe Biden on Monday warned that Covid-19 cases could yet rise if more people don't get vaccinated.

"We know there will be advances and setbacks, and we know that there are many flare-ups that could occur," he said. "But if the unvaccinated get vaccinated, they will protect themselves and other unvaccinated people around them" (Cunningham, "PowerPost," Washington Post, 5/17; Reuters, 5/17; Reed, "Vitals," Axios, 5/18; Slotnik/Hassan, New York Times, 5/12; Owens, "Vitals," Axios, 5/13; Ansari, Wall Street Journal, 5/17; Lovelace, CNBC, 5/17).