WASHINGTON (AFP) - US officials on Sunday (Jan 3) defended the stumbling campaign to vaccinate millions of Americans against the coronavirus, saying they expected much more to be done in coming weeks after delays.

"There have been a couple of glitches, that's understandable," top US scientist Anthony Fauci said on ABC. He said there would always be challenges in "trying to get a massive vaccine program started and getting off on the right foot."

Some 4.2 million Americans have received initial doses of the two-dose vaccines from Pfizer-BioNTech or Moderna, but that is far below official predictions of 20 million by the new year.

Part of the problem, Surgeon General Jerome Adams said on CNN, is that "this virus also occurred in the midst of a surge, and a lot of the local capacity to be able to vaccinate was being used for testing and responding to surges."

President Donald Trump has placed the onus on the states to orchestrate vaccine distribution once they receive their supplies.

"The vaccines are being delivered to the states by the Federal Government far faster than they can be administered!" he tweeted Sunday.

Trump dismisses death toll

Fauci said he saw "some little glimmer of hope" in the fact that 500,000 people are now being inoculated a day, a far better number than when the program started last month, and "I think we can get there if we really accelerate, get some momentum going."

Adams said he, too, expects vaccinations to "rapidly ramp up in the new year."

Troubling reports have emerged of vaccine going bad due to poor organisation, lack of healthcare professionals to administer it and, in one isolated case, sabotage.

Some people have also waited in line for hours only to be turned away.

In Tennessee, elder citizens, some with walkers, were reported standing along a busy highway while waiting for their vaccinations.

Health officials also rejected unsubstantiated suggestions by Trump that the Covid-19 toll - total deaths now surpass 350,000 - has been exaggerated.

The president tweeted Sunday that "the number of cases and deaths of the China Virus is far exaggerated in the United States because of @CDCgov's ridiculous method of determination compared to other countries, many of whom report, purposely, very inaccurately and low. 'When in doubt, call it Covid.' Fake News!"

But Adams, who was nominated by Trump, said he saw no reason to question the numbers from the federal Centers for Disease Control (CDC).

Fauci said that "those are real numbers, real people and real deaths."