More than 25 million COVID-19 cases have been recorded in the United States since the pandemic began as President Joe Biden's chief of staff Ron Klain said the Trump administration did not have a coronavirus vaccine distribution plan in place.
The grim milestone was reached only five days after the US, the world's wealthiest and hardest-hit nation, recorded 400,000 deaths from the disease.
Mr Biden has made fighting the coronavirus a priority and is pushing for Congress to approve a $1.9-trillion relief package that would include billions of dollars to boost vaccination rates.
Mr Biden has said he wants 100 million people vaccinated within his first 100 days in office, and he has called for Americans to wear masks for 100 days.
Countries around the world are in a race against time to get their populations inoculated before the coronavirus mutates into a strain that could resist newly approved vaccinations.
White House Chief of Staff Ron Klain said on Sunday there was no distribution plan for the coronavirus vaccine set up by the Trump administration as the virus raged in its last months in office.
“The process to distribute the vaccine, particularly outside of nursing homes and hospitals out into the community as a whole, did not really exist when we came into the White House,” Mr Klain said on NBC’s “Meet the Press.”
"We're going to set up these federal vaccination centers to make sure that in states that don't have enough ... we fill those gaps," Mr Klain told the NBC News show "Meet the Press."
"We need more vaccine, we need more vaccinators and we need more vaccine sites."
Variants 'concerning'
Vivek Murthy, Mr Biden's nominee for surgeon-general, told ABC News on Sunday that 100 million doses in 100 days was "a floor, not a ceiling" and cautioned about new strains.
"The variants are very concerning," Dr Murthy told the network.
"It's up to us to adapt and stay ahead," he added.
The US caseload remains by far the world's highest in absolute terms.
India, where the population is about four times larger than in the US, has the second-highest caseload with about 10.6 million cases, according to Johns Hopkins.
After the first COVID-19 case was reported in the US in January 2020 it took until late April for the figure to pass one million. The overall number of cases has followed an almost exponential curve upwards since then.
A nurse tends to a COVID-19 patient at St. Joseph Hospital in Orange, California. Source: AAP
Xavier Becerra, Mr Biden's secretary of health and human services nominee, likened the COVID-19 trajectory under Mr Trump to a plane about to crash.
"We've got to pull it up and you aren't going to do that overnight, but we'll pull it up - we have to pull it up," he told CNN.
"Failure is not an option here."
Last week, Johns Hopkins announced more than 400,000 people in the US had died from COVID-19, a grim marker that came one day before Mr Biden's inauguration.
The US has now recorded 25,003,695 million cases, according to the Baltimore-based university's coronavirus tracking website - though with testing shaky at the start of the pandemic, the real toll is believed to be much higher.
