Get PolitiFact in your inbox.

X posts
stated on May 24, 2021 in Twitter:
"The CDC lowered the PCR threshold while no longer recording asymptomatic cases...but only for the vaccinated."
true false
Michael Majchrowicz
By Michael Majchrowicz June 3, 2021

The CDC did not change its criteria for what is considered a breakthrough positive COVID case

If Your Time is short

  • While it’s true the Centers for Disease Control and Prevention are no longer officially scrutinizing asymptomatic breakthrough infections, the agency has not "lowered" the general cycle threshold for determining COVID-19 cases.

Widely shared social media posts wrongly claim that the Centers for Disease Control and Prevention changed its testing parameters for vaccinated individuals so that fewer cases of COVID-19 infections would be recorded.

One such post on Twitter, which was also shared across Facebook, questioned why the CDC would "deliberately lower the PCR test threshold while no longer recording asymptomatic cases" for those who are vaccinated.

But that’s not what happened.

The post was flagged as part of Facebook’s efforts to combat false news and misinformation on its News Feed. (Read more about our partnership with Facebook.)

First, PCR stands for polymerase chain reaction and is one method available to test for active COVID-19, by screening nasal and throat samples for the presence of viral RNA.

The National Human Genome Research Institute described PCR as "‘molecular photocopying,’... a fast and inexpensive technique used to ‘amplify’ — copy — small segments of DNA." The PCR method is widely hailed in the medical community as the gold standard when it comes to reliable and accurate COVID-19 testing.

Using this method, samples are replicated again and again so that any viral genetic material can be more easily detected. 

The Twitter claim appears to stem from the CDC’s announcement that, starting May 14, it changed the way it monitors and reports "breakthrough" COVID-19 cases. Breakthrough cases are infections diagnosed in people who have been fully vaccinated. The agency said it would focus its monitoring of reported vaccine breakthrough cases only on those cases that involved patients who were hospitalized or died.

At the time, the change spawned a similarly False social media claim that the government’s action was intended to obscure data and paint a rosier picture of the outbreak. Rather, the CDC said the move was intended to provide a better means of zeroing in on more complete data on the most concerning cases, since not all people with breakthrough infections can be identified — particularly those with asymptomatic or mild illness who do not get tested.

The new approach also is part of an effort to collect more data on variant strains of the virus.

The agency set a benchmark to determine which positive breakthrough samples are further analyzed for evidence of a variant. That benchmark is described as a "cycle threshold value" — that’s the number of cycles necessary to spot the virus and is commonly abbreviated as "Ct." For a breakthrough case to be further analyzed, the test must have a Ct value of 28 or lower. The measure indicates a high level of virus. But the move did not signify a "lower threshold" for what is considered a positive COVID case, as the Twitter claim suggests.

CDC spokeswoman Jade Fulce said in a statement that, when it comes to determining which positive samples are assessed for presence of a variant strain, any Ct value higher than 28 is pretty much moot since it indicates the viral load is too small.

"The criteria for determining if a sample is positive is defined by the data submitted to FDA for the Emergency Use Authorization. This criteria has not changed nor does it change whether the case is a breakthrough case or not," Fulce said. "The Ct value ≤28 is not used to define whether a specimen is positive or negative for COVID. It is only used for determining whether a specimen that tests positive could be submitted for SARS-CoV-2 sequencing. It is not specific to vaccine breakthrough cases."

Our ruling

The post claims that the CDC lowered the benchmark cycle threshold used to determine what’s considered a positive COVID case, which is not true. The criteria for identifying COVID cases — breakthrough infections or otherwise — have not changed. 

We rate this claim False.

Our Sources

Twitter post, May 24, 2021

Centers for Disease Control and Prevention, Frequently Asked Questions about Coronavirus (COVID-19) for Laboratories, accessed May 28, 2021

Email interview with Jade Fulce, spokeswoman for the CDC, May 27, 2021

Email interview with Dr. Anna Durbin, professor, Johns Hopkins Bloomberg School of Public Health, May 27, 2021 

PolitiFact, WHO did not say PCR tests grossly inflate positive test numbers, Jan. 22, 2021

National Human Genome Research Institute, Polymerase Chain Reaction (PCR) Fact Sheet, accessed May 28, 2021

USA Today, COVID-19 testing: CDC loosens restrictions for vaccinated people, May 15, 2021

Browse the Truth-O-Meter

More by Michael Majchrowicz

The CDC did not change its criteria for what is considered a breakthrough positive COVID case

Support independent fact-checking.
Become a member!

In a world of wild talk and fake news, help us stand up for the facts.

Sign me up