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Graph does not show US has reached herd immunity against the coronavirus

August 7, 2020 GMT

CLAIM: A graph from Johns Hopkins University displaying the rate of positive COVID-19 tests in the United States over time shows the country has reached herd immunity, and probably reached it in May.

AP’S ASSESSMENT: False. Social media users are misinterpreting the graph, which is meant to indicate whether a community is doing enough testing, not show the spread of the virus in the population. The United States is not close to reaching herd immunity, experts say.

THE FACTS: This week, a lengthy Facebook post with 155,000 views falsely claimed that a declining positivity rate for COVID-19 tests means the U.S. has reached herd immunity, the point where there is a sufficiently high proportion of immune people in the population to stop the spread of the disease.

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The Facebook user, identifying himself as a “Health Policy Expert,” used the graph from Johns Hopkins University’s Coronavirus Resource Center to argue that a dip in positive cases as a percentage of total tests indicates the coronavirus is “petering out.”

“Ask any biostatistician what it means when you test hundreds of thousands of people a day for an infectious disease and return a consistently lowering positivity rate,” the post reads. “I’ll give you a clue: it means heard immunity has been reached and the virus is dying out.”

However, Dr. Jennifer Nuzzo, the lead epidemiologist on the team that made the graph at Johns Hopkins, told The Associated Press that’s not at all what it shows. She said people were misinterpreting the graph as showing how easily the virus is spreading.

“You can’t say this is a measure of the amount of infection that’s occurring in the community,” Nuzzo said. “It is a measure of if you are doing enough testing.”

The number of positive tests as a percentage of total tests provides insight into whether more testing is needed and which members of the population are being tested, according to Nuzzo’s team.

A high positivity rate suggests that a community might be testing mostly the sickest patients, and could be missing milder or asymptomatic cases.

A lower positivity rate may indicate a community is also testing patients with milder or no symptoms.

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In May, the World Health Organization recommended that governments hold off on reopening until a 5% or lower positivity rate is maintained for at least 14 days. While some states meet that guideline, according to Johns Hopkins University’s tracking data, most do not.

On the graph, which tracks the total number of daily tests, daily positive tests, and positive tests as a percentage of daily tests for the U.S. from April to August, the positivity rate has fluctuated, and is experiencing a slight dip in August. 

Nuzzo cautions that this recent decline should not be interpreted as an indicator of widespread immunity, nor should it be falsely understood as a sign the virus has become less transmissible. 

Instead, it probably shows that harder-hit states like Arizona, Georgia and Texas are getting a handle on their cases through efforts to slow the spread of the virus in those hotspots, Nuzzo said.

Claims that the U.S. has reached herd immunity are also false.

“We don’t think we can achieve herd immunity until maybe as much as 60% of the population has been infected,” Nuzzo said. “We don’t want 60 percent of us to get this virus.”

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This is part of The Associated Press’ ongoing effort to fact-check misinformation that is shared widely online, including work with Facebook to identify and reduce the circulation of false stories on the platform.

Here’s more information on Facebook’s fact-checking program: https://www.facebook.com/help/1952307158131536