The US coronavirus death toll has passed 600,000, according to Johns Hopkins University data

• The US death toll from COVID-19 has passed 600,000, according to data from Johns Hopkins University.
• Pre-pandemic life has largely returned in the US because of the vaccine rollout.
• But some vaccine hesitancy and procrastination is posing a threat to reaching herd immunity.

The US reached a grim new milestone Tuesday: The nation's known death toll from COVID-19 surpassed 600,000, according to data from Johns Hopkins University.

The university's COVID-19 dashboard now indicates 600,012 Americans have died since the pandemic began in 2020.

No other country has reported more COVID-19 deaths, and scientists say the true death toll is most likely higher than official reports.

But the pace of death has fallen dramatically in the US since vaccines were first authorized six months ago. Daily COVID-19 deaths have decreased about 85% since mid-December - to 330 a day on average from about 2,150 a day.

The US has also seen its rate of new COVID-19 cases and hospitalizations plummet: At the height of the US outbreak in January, the country reported more than 300,000 new COVID-19 cases in a single day. For most of June it has been reporting a seven-day average below 15,000 a day, according to the Centers for Disease Control and Prevention.

New York, the original US epicenter, reported a test positivity rate of 0.35% on Sunday - the state's lowest rate of the pandemic.

Disease experts still worry that progress is tenuous, though.

In May, President Joe Biden said he hoped 70% of Americans would receive at least one of their shots by July 4. It's unlikely the US will reach that goal now, however as vaccination rates lag in several states.

At its peak in April, the US was administering more than 3.3 million daily doses, on average. But as of last week, that seven-day average had dropped below 1 million.

Just over 43% of people in the US are fully vaccinated against the disease, meaning they have received Johnson & Johnson's single-dose vaccine or both doses of the two-shot Pfizer-BioNTech or Moderna vaccines. And more than 52% of Americans have received at least one dose.

Scientists generally estimate that getting to herd immunity - the threshold beyond which the virus can't easily pass from person to person - would require the US to fully vaccinate 70% to 85% of its residents.

In reality, that threshold could be slightly lower: Israel, for instance, appears to have reached herd immunity after vaccinating just 60% of its citizens, or roughly 80% of its adult population.

In any case, vaccine hesitancy has posed a challenge to reaching herd immunity in the US.

A Gallup poll released last week found that one in four Americans still didn't want to get vaccinated against COVID-19 - most commonly citing a lack of trust in the shots or concern about side effects. NBC News reported Monday that the vast majority of COVID-19 patients currently in US hospitals were unvaccinated.

Even so, pre-pandemic life has largely returned in the US. All 50 states loosened or eliminated remaining lockdown restrictions over the past month, including mask mandates and capacity restrictions on restaurants and other businesses.

Air travel has also inched closer to pre-pandemic levels as more Americans return to the skies. The number of daily travelers recorded by the Transpiration Security Administration on Friday exceeded 2 million for the first time in more than a year.