Pfizer Inc expects to deliver more than 13 million doses of its COVID-19 vaccine per week to the United States by the middle of March, more than doubling its shipments from early February, a top Pfizer executive said in prepared testimony ahead of a Tuesday congressional hearing.

Pfizer is on track to deliver 120 million doses of its two-dose regimen by the end of March, said John Young, Pfizer's chief business officer.

Pfizer is also prepared to provide a total of 300 million shots to the United States by the end of July and has raised global production expectations for 2021 to at least 2 billion doses, he said.

In his own prepared remarks, Moderna Inc President Stephen Hoge said the drugmaker plans to deliver 100 million doses of its two-dose shot by the end of March, and 300 million by the end of July.

Johnson & Johnson believes it will be able to ship at least 20 million doses of its single-dose shot to the United States by the end of March after receiving US regulatory authorization and 100 million doses by mid-year 2021, said Vice President of Medical Affairs Richard Nettles.

The comments were prepared ahead of a US congressional hearing on vaccine availability to be held by the House Committee on Energy and Commerce on Tuesday as the United States crossed the staggering milestone of 500,000 COVID-19 deaths.

The remarks put the United States on track to receive 240 million doses by the end of March, enough to inoculate 130 million Americans, and 700 million doses by mid-year.

AstraZeneca Plc, which is running a US trial for its coronavirus vaccine, believes it can quickly adapt its shot to new variants of the virus in its laboratory, said Ruud Dobber, company president, North America.

A highly contagious COVID-19 variant has become prevalent in South Africa and has turned up in several US states.