In its latest about-face, the Centers for Disease Control and Prevention (CDC) has reversed controversial COVID-19 testing guidelines that were posted to the agency's website last month, reportedly over the objections of its own scientists.

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On August 24, the CDC updated its testing guidelines to say that being exposed to a person with COVID-19 didn't necessarily warrant a test for those who are low-risk or not showing any symptoms, Live Science previously reported. 

Now, the agency has reverted back to previous guidelines, saying that close contacts of a person infected with SARS-CoV-2 should be tested. That's because people can transmit the virus before, or without ever showing any symptoms.

If you have been in close contact with an infected person, such as within 6 feet (1.8 meters) for at least 15 minutes and do not have symptoms, "you need a test," the CDC's guidance now reads.

Despite this flip-flopping, the science on asymptomatic or presymptomatic transmission has not changed: people who don't show symptoms can transmit the virus.

That's why last month's abrupt switch in guidelines was met with strong criticism from public health experts. 

President Donald Trump has previously stated that less testing would lead to fewer cases, so some public health experts were concerned the guidelines were changed for political, rather than scientific reasons.

"It is unconscionable that recommendations, which should follow only the science, are being modified to enable [maybe even ensure] underreporting of COVID-19 cases at this critical juncture," Krys Johnson, an assistant professor of instruction in the Department of Epidemiology and Biostatistics at Temple University in Pennsylvania previously told Live Science in an email.

It's not clear what percentage of COVID-19 cases are asymptomatic, but the CDC estimates about 40 percent of people never show symptoms. 

"If each of these people goes about their daily lives, this pandemic will continue to impact our country and daily lives for the foreseeable future, regardless of the advent of a vaccine," Johnson said at the time.

After the guidance was updated last month, the Department of Health and Human Services Assistant Secretary, Adm. Brett Giroir defended the decision, telling CNN that the point of the new guidance wasn't to do "less" testing, but more "appropriate" testing.

Citing internal documents and people familiar with the subject, a New York Times report published yesterday (September 18) alleged that the updated guidance was written by the Department of Health and Human Services, did not go through the rigors of the CDC's scientific review process and was published on its website despite strong opposition from CDC scientists.

The CDC said today's change is a "clarification."

Because many cases are driven by people who don't show symptoms, asymptomatic people who have had close contact with SARS-CoV-2-positive people need to be tested, the clarification says.

This article was originally published by Live Science.