The number of Americans who have died from Covid-19 has reached 600,012 - the most of any nation - according to data from Johns Hopkins University.
The US also ranks highest in total number of recorded cases, with nearly 33.5 million infections since 2020.
This latest milestone comes as President Joe Biden's goal of getting 70% of US adults vaccinated by 4 July appears increasingly likely to fail.
Over 173 million people, around 52% of the US, have had at least one dose.
Brazil and India have reported the next highest death tolls, with Brazil at more than 488,000 deaths and India at more than 377,000.
Slowing death and vaccination rates
It took around four months for the US to go from 500,000 to 600,000 deaths - about as long as it took to go from none to 100,000. It marks a significant change from the height of the pandemic when the death toll jumped from 300,000 to 400,000 in one month last winter.
But the country's vaccination rate has begun to fall to around 1m doses administered per day - down from a high this April of nearly 3.4m.
Roughly 43% of the US population, or about 144 million Americans, are fully vaccinated, according to the Centers for Disease Control and Prevention (CDC). The CDC says people are fully vaccinated at least two weeks after their final vaccine dose.
It comes as the CDC officially labels the Delta mutation, first discovered in India, a "variant of concern". Delta variant cases amount to 10% of all new infections, the CDC said, and is growing in comparison to the dominant Alpha variant, first identified in Kent, UK.
Headache and runny nose linked to Delta variant
Though a majority of adult Americans have received at least one dose, the percentages vary wildly from state to state. Vermont has fully vaccinated 71% of its residents, but only 36% of Mississippians have received both jabs, according to a New York Times database.
A recent Kaiser Family Foundation poll found around a third of US adults were not planning on getting vaccinated yet - leading states and companies to offer countless vaccine incentives.
Ohio has been selecting one vaccinated resident each week to win $1m (£708,000). On Tuesday, California will give $1.5m each to 10 residents. Other winnable items include alcohol, cannabis, guns, food vouchers and gift cards.
The White House is also working to boost vaccinations, with Vice-President Kamala Harris beginning a national tour to promote jabs on Monday.
The same day, US drug maker Novavax announced that its vaccine was found to be 90.4% effective after testing was conducted on 30,000 participants.
If this vaccine is eventually approved, it would be the fourth coronavirus vaccine to hit the US market.
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The Biden administration has already ordered enough doses of the existing vaccines for the entire US population, US media report, so Novavax may become part of the global vaccine-sharing deal to donate doses.
'Grand re-opening'
On Monday night, the governor of California - the most populous US state - announced a "grand re-opening".
The state which ordered the first coronavirus lockdown will now allow vaccinated people to not wear masks or socially distance in most settings. Public health measures remain for events with over 5,000 people.
Across the country, New York is also beginning a return to normalcy.
On Tuesday, the Governor Andrew Cuomo lifted nearly all restrictions after the state's vaccination rate passed 70%.
"We can now return to life as we know it," declared Mr Cuomo, adding that the new rules were effective immediately.
The US also ranks highest in total number of recorded cases, with nearly 33.5 million infections since 2020.
This latest milestone comes as President Joe Biden's goal of getting 70% of US adults vaccinated by 4 July appears increasingly likely to fail.
Over 173 million people, around 52% of the US, have had at least one dose.
Brazil and India have reported the next highest death tolls, with Brazil at more than 488,000 deaths and India at more than 377,000.
Slowing death and vaccination rates
It took around four months for the US to go from 500,000 to 600,000 deaths - about as long as it took to go from none to 100,000. It marks a significant change from the height of the pandemic when the death toll jumped from 300,000 to 400,000 in one month last winter.
But the country's vaccination rate has begun to fall to around 1m doses administered per day - down from a high this April of nearly 3.4m.
Roughly 43% of the US population, or about 144 million Americans, are fully vaccinated, according to the Centers for Disease Control and Prevention (CDC). The CDC says people are fully vaccinated at least two weeks after their final vaccine dose.
It comes as the CDC officially labels the Delta mutation, first discovered in India, a "variant of concern". Delta variant cases amount to 10% of all new infections, the CDC said, and is growing in comparison to the dominant Alpha variant, first identified in Kent, UK.
Headache and runny nose linked to Delta variant
Though a majority of adult Americans have received at least one dose, the percentages vary wildly from state to state. Vermont has fully vaccinated 71% of its residents, but only 36% of Mississippians have received both jabs, according to a New York Times database.
A recent Kaiser Family Foundation poll found around a third of US adults were not planning on getting vaccinated yet - leading states and companies to offer countless vaccine incentives.
Ohio has been selecting one vaccinated resident each week to win $1m (£708,000). On Tuesday, California will give $1.5m each to 10 residents. Other winnable items include alcohol, cannabis, guns, food vouchers and gift cards.
The White House is also working to boost vaccinations, with Vice-President Kamala Harris beginning a national tour to promote jabs on Monday.
The same day, US drug maker Novavax announced that its vaccine was found to be 90.4% effective after testing was conducted on 30,000 participants.
If this vaccine is eventually approved, it would be the fourth coronavirus vaccine to hit the US market.
G7 leaders promise one billion vaccine doses
How many vaccines are rich countries sharing?
The Biden administration has already ordered enough doses of the existing vaccines for the entire US population, US media report, so Novavax may become part of the global vaccine-sharing deal to donate doses.
'Grand re-opening'
On Monday night, the governor of California - the most populous US state - announced a "grand re-opening".
The state which ordered the first coronavirus lockdown will now allow vaccinated people to not wear masks or socially distance in most settings. Public health measures remain for events with over 5,000 people.
Across the country, New York is also beginning a return to normalcy.
On Tuesday, the Governor Andrew Cuomo lifted nearly all restrictions after the state's vaccination rate passed 70%.
"We can now return to life as we know it," declared Mr Cuomo, adding that the new rules were effective immediately.