In several Twitter and Facebook promotions for a segment from the Sept. 16 episode of “The Rachel Maddow Show,” MSNBC and the show claimed achieving herd immunity would kill roughly 6.4 million Americans.

Verdict: False

Maddow’s calculations are based on a fatality rate derived from only confirmed COVID-19 cases, a metric that does not account for the many people who contract the disease but go undiagnosed. When those people are included, the fatality rate falls significantly. Based on the more accurate infection fatality rate metric, an estimated 1.4 million would die if herd immunity was achieved, not the roughly 6.4 million projected by Maddow.

Fact Check:

MSNBC and Maddow’s team appeared to highlight the figure in at least four tweets, which collectively garnered over 3,500 retweets, and at least five Facebook posts, which collectively garnered over 10,000 shares. The social media posts were promoting last Wednesday’s episode of “The Rachel Maddow Show,” where Maddow initially claimed that President Donald Trump is “aiming for” roughly 6.4 million Americans to die in order to achieve herd immunity against COVID-19.

215 million Americans would need to be infected with the coronavirus to reach herd immunity, a strategy Pres. Trump has said would make the virus “go away.”

This strategy would result in 6,385,500 deaths based on the current US fatality rate of 2.97%. https://t.co/5beVfRxwrx

— MSNBC (@MSNBC) September 18, 2020

Herd immunity is a phenomenon that “occurs when a large portion of a community (the herd) becomes immune to a disease, making the spread of disease from person to person unlikely,” according to Mayo Clinic. It can be achieved through vaccination or infection. Infectious disease experts have warned against using herd immunity to end the coronavirus pandemic due to the associated cost on human life, per the Wall Street Journal.

Maddow came to her 6,385,500 figure by multiplying the 2.97 percent observed fatality rate among confirmed COVID-19 cases, known as the case fatality rate, by 215 million, the equivalent of the 65 percent needed to allegedly achieve herd immunity of the roughly 330 million U.S. population. She then adjusted her fatality rate to 1 percent in order to “give him [Trump] the benefit of the doubt” and came up with 2,150,000 dead.

However, an analysis of Centers for Disease Control data by Check Your Fact shows that her math is misleading, and experts said that using the case fatality rate does not paint an accurate picture for potential COVID-19 deaths while reaching herd immunity. (RELATED: Viral Post Conflates COVID-19 Antibody And Viral Tests)

“She is using the case fatality ratio to make that calculation, which is not correct because it only employs lab confirmed infections as the denominator, and we know there are more infections,” explained Vincent R. Racaniello, a Higgins professor in the Department of Microbiology and Immunology at Columbia University’s College of Physicians and Surgeons, in an email to the Daily Caller News Foundation.

“What would be more accurate is the infection fatality ratio, which for denominator uses the actual number of infections. That cannot be determined but is extrapolated statistically.”

Amesh Adalja, a senior scholastic at the Johns Hopkins University Center for Health Security, and Andrew Azman, an assistant scientist affiliated with the Johns Hopkins Bloomberg School of Public Medicine’s Epidemiology Department, also agreed in emails to the DCNF: Azman said, “That is wrong. I think she is mixing up disease and infection,” while Adalja said, “The case count is an underestimate and the actual infection fatality rate is probably around 0.66%.”

The infection fatality rate (IFR), also known as the infection fatality ratio, that the experts referenced accounts for the many people who have contracted COVID-19 but gone undiagnosed. The number of COVID-19 infections nationwide may be more than 6 to 24 times higher than the confirmed cases, according to a seroprevalence study conducted by the CDC in July.

One meta-analysis of 24 IFR estimates published in July on medRxiv found the IFR for COVID-19 to be 0.68 percent. The CDC website on Sept. 10 listed the current best estimate for overall IFR at 0.65 percent based on data the agency received through June 29, though it has since updated to the page to reflect differences in the IFR for various age groups.

Multiplying the CDC’s 0.65 percent IFR by Maddow’s 215-million figure, the number of U.S. deaths that would occur while reaching herd immunity would be 1,397,500. That number is 4,988,000 lower than her 6,385,500 figure and 752,500 lower than her 2,150,000 figure.

In a statement to the DCNF, a spokesperson for MSNBC said they “stand by their reporting.” (RELATED: Did Trump Call The Coronavirus A ‘Hoax’ At His South Carolina Rally?)

“Our report was designed to demonstrate that a herd immunity strategy would have a much higher death toll than a prophylactic Covid strategy. We used the most recent available numbers of known Covid cases, approximately 6.6 million, and the number of known Covid deaths, approximately 200,000,” the spokesperson said. “Those numbers gave a known mortality rate of 2.97 percent which would mean more than 6 million people dying.”

The spokesperson also acknowledged that “if you were to use an IFR of 0.65%, there would be 1,397,500 deaths” and said that “no matter which way you calculate the numbers, they support that assertion” that a “herd immunity strategy would have a much higher death toll than a prophylactic Covid strategy.”

MSNBC continued to highlight the roughly 6.4 million figure in social media promotions for the segment even after Check Your Fact notified them that their numbers were based on a flawed understanding of statistics around COVID-19 fatality rates.

At the time of publication, the CDC website lists the current best estimate IFR as 0.003 percent for people ages zero to 19, 0.02 percent for people ages 20 to 49, 0.5 percent for people ages 50 to 69 and 5.4 percent for people 70 and older.

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