Most Americans could be vaccinated for COVID-19 by July of 2021, Robert Redfield, head of U.S. Centers for Disease Control and Prevention (CDC) told a U.S. Senate committee on Wednesday.

He expects there to be about 700 million doses of vaccines available by late March or April, enough for 350 million people, and the vaccinations to take place over several months. 

"I think that's going to take us April, May, June, you know, possibly July, to get the entire American public completely vaccinated," Redfield told the U.S. Senate Health, Education, Labor and Pensions Committee. 

Redfield, U.S. Food and Drug Administration head Stephen Hahn, U.S. National Institute of Allergy and Infectious Diseases head Anthony Fauci and Health and Human Services official Brett Giroir were testifying on the COVID-19 pandemic, which has caused more than 200,000 deaths in the United States. 

There is no vaccine for COVID-19 yet, but there are several in late stage trials here, including from Pfizer, Moderna and Johnson & Johnson Companies have begun manufacturing the vaccine in anticipation of a fast regulatory authorization once they are shown to work. 

Fauci said he expects 50 million doses to be available in November and 100 million by the end of December. He expects a total of 700 million doses by April. 

Health officials and President Donald Trump have presented different views about when the vaccines will be ready for most Americans. The process for deciding how to distribute vaccines falls largely to the CDC. 

Redfield said Operation Warp Speed, the government group with officials from the departments of Health and Human Services and Defense, will ultimately decide how to allocate the vaccines. 

Trump says may block stricter FDA guidelines for COVID-19 vaccine 

Trump said on Wednesday he may or may not approve any new, more stringent FDA standards for an emergency authorization of a COVID-19 vaccine, saying such a proposal would appear political. 

Trump has repeatedly said a vaccine for COVID-19, the disease caused by the coronavirus, could be ready for distribution ahead of the November 3 presidential election. 

The Washington Post reported on Tuesday the U.S. Food and Drug Administration would issue the guidance to boost transparency and public trust as health experts have become increasingly concerned the Trump administration might be interfering in the approval process to rush out a vaccine. 

Trump, however, questioned why a vaccine would need to be delayed and said such a proposal by the FDA would appear to be politically-driven. 

"We're looking at that and that has to be approved by the White House. We may or may not approve it," Trump told a White House news conference, when asked about the Post report. 

"That sounds like a political move. Because when you have Pfizer, Johnson & Johnson, Moderna, these great companies, coming up with the vaccines, and they've done testing and everything else, I'm saying why would they have to be adding great length to the process."

Trump added he had "tremendous trust" in those companies. 

(Cover: A large mask hangs on the face of a lion statue standing outside of the main branch of the New York Public Library in the Manhattan borough of New York City, U.S., July 1, 2020. /VCG）