A number of U.S. public health officials have warned against the Trump administration's support for scientists who are pushing against lockdowns to fight the coronavirus, while also pushing for "herd immunity" against the virus.

Dr. Anthony Fauci, America's top infectious disease expert, called the White House's herd immunity proposal "total nonsense."

The idea "misses the basic point that we're all connected," former director of the U.S. Centers for Disease Control and Prevention Dr. Thomas Frieden told CNN. He added that the best way to achieve widespread immunity will be through a vaccine. 

William Haseltine, chair and president of ACCESS Health International, said on CNN's "New Day" on Wednesday that "herd immunity is another word for mass murder."

He said if the "herd immunity" strategy is to be implemented and let the pandemic run its course, "we are looking at two to six million Americans dead – not just this year but every year." 

"This is an unmitigated disaster for our country – to have people at the highest levels of our government countermanding our best public health officials," Haseltine said. "We know this epidemic can be put under control. Other countries have done it. We are doing the opposite." 

The World Health Organization is also pushing against using herd immunity as a strategy against the COVID-19 crisis, calling such a move "simply unethical."

Read more: Herd immunity against COVID-19 'simply unethical': WHO chief

But the White House has been embracing the idea behind herd immunity to combat the coronavirus, while the president criticizes what he calls "unscientific lockdowns" as well as the failing U.S. economy.

How did herd immunity become such a contentious issue in the fight against the coronavirus?

What is herd immunity?

Herd immunity means a virus can no longer spread easily throughout a population because people are immune to it. Ideally, at least 70 percent of a population needs to be immune from the virus before herd immunity is a useful option.

"Never in the history of public health has herd immunity been used as a strategy for responding to an outbreak," Tedros Adhanom Ghebreyesus, director-general of the WHO, said.

The WHO website says the majority of people in most countries remain susceptible to the virus – and new research shows less than 10 percent of the U.S. population have been infected by COVID-19.

In order to create a herd of protection around other people, 60 percent to 70 percent of the population would have to become infected.

Why are people saying it's too early for herd immunity?

Medical associations, including the American Public Health Association, Johns Hopkins Center for Public Security of the Johns Hopkins School of Public Health and the Public Health Institute, are saying that COVID-19 carries a much greater risk of severe diseases and deaths compared to other infections.

A number of these organizations have been critical of the Great Barrington Declaration, which was signed and released early in October by health professionals that are embracing the "herd immunity" policy for the virus, while arguing against the current lockdown method.

But critics say that the declaration would haphazardly sacrifice lives and is not based on science.

These groups say that masks and social distancing are the best ways to continue the fight against the coronavirus.

Also, reports note that the current extent of natural infections from the coronavirus that could lead to herd immunity is unknown. And without a vaccine, more people would die waiting for immunity to actually kick in.

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