CDC director: PCR tests can stay positive up to 12 weeks
Walensky admits change in isolation period based on "what we thought they would be able to tolerate."
Almost from the beginning of their use during the pandemic, there have been questions about just how sensitive PCR tests are and the possibility of false positives.
Now Centers for Disease Control (CDC) Director Dr. Rochelle Walensky seems to be admitting that PCR tests have inherent sensitivity flaws over a year and a half their use.
Walensky told “CBS Mornings” on Dec. 29 that the recently updated CDC quarantining guidelines don’t require testing at the end of isolation because PCR tests can stay positive for up to 12 weeks,
Walensky said that "we would have people in isolation for a very long time if we were relying on PCRs."
Since at least the summer of 2020, PCR tests were documented as using too high of a cycle threshold, thereby registering dead virus and resulting in false positives. By the Fall of 2020, the CDC and the World Health Organization (WHO) had both indicated any threshold over 28 was too high.
In North Carolina, the Department of Health and Human Services and its former Secretary Mandy Cohen both have stated that PCR tests used by the state lab follow the test instructions for use, and that "the cutoff for positive clinical specimens is 37.” It was also noted in Oct. of 2020 that other labs, such as LabCorp, could be using cycles as high as 38. It is unclear if those rates were brought into compliance with CDC and WHO suggestions.
During a CNN interview, Walensky also made an astonishing remark about the shortening of the quarantine period.
“It really had a lot to do with what we thought people would be able to tolerate,” Walensky told CBS on why the CDC has shortened the isolation period from 10 days to 5 days.
With regard to the Omicron variant in the CBS interview, Walensky also called into doubt rapid antigen tests, which the Biden administration, CDC, and state officials have been pushing heavily heading into the holidays.
Walensky now says it’s unclear whether or not a negative test result indicates that an individual is no longer spreading the virus.
“We know it performs really well during that period where you’re initially infected, but the FDA has not at all looked at whether … your positive antigen really does correlate with whether you’re transmissible or not,” she said.
“What we do know is about 85 percent to 90 percent of viral transmission happens in those first five days, which is why we really want people to stay home during that period of time,” Walensky said. “And then mask for the rest of the time to capture that last 10 percent to 15 percent.”
She told CBS that rapid tests could be less sensitive when it comes to the Omicron, but still work "quite well." Walensky urged people to continue using them. According to ABC News, Walensky urged their use "especially in places where people are being tested regularly." One such regular testing area mentioned was schools.
“We do know that the most sensitive test you can do is a PCR test,” Walensky said. “So if you have symptoms and you have a negative antigen test, we do ask you to go and get a PCR to make sure those symptoms are not attributable to COVID.”
The CDC director also denied the lack of such testing was related to supply chain issues and a shortage of antigen tests in the U.S.
On the same day Walensky made her remarks, CNN medical correspondent Elizabeth Cohen made several claims about the most popular at-home COVID tests, the BinaxNOW antigen test, and its effectiveness in detecting Omicron.
According to Cohen, a rapid antigen test will be wrong 35% of the time for people who have COVID with symptoms and wrong 64% of the time for those with COVID without symptoms. Where these specific percentages came from was not shared by Cohen, but she did say her assertions were based on statements by Dr. Anthony Fauci.
Walensky's comments have people asking how long the CDC has known and accusations the agency has misled the public yet again.
Individuals online have pointed to a July 21, 2021 "Lab Alert" issued by the CDC as proof the CDC knew the tests were faulty. However, that alert served as an advance warning to labs around the country to begin identifying and using an "FDA-authorized" alternative to the "Real-Time" or "RT-PCR" tests.
"After December 31, 2021, CDC will withdraw the request to the U.S. Food and Drug Administration (FDA) for Emergency Use Authorization (EUA) of the CDC 2019-Novel Coronavirus (2019-nCoV) Real-Time RT-PCR Diagnostic Panel, the assay first introduced in February 2020 for detection of SARS-CoV-2 only," the July 17, 2021, lab alert reads.
The CDC has said that this withdrawal request is due to multiple new tests becoming available coinciding with less use of the Real-Time test.
According to various journal entries at the CDC's website, including an entry from February 2021, Real-Time PCR tests are very sensitive and require specialized equipment to perform.
Also of interest to North Carolinians, at least one file on the FDA's website says the Real-Time PCR test has been used by LabCorp in the Tarheel state as part of the "Labcorp At Home COVID-19 Test Home Collection Kit."
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