PCR tests on vaccinated and unvaccinated people are evaluated using the same criteria; the CDC didn’t change criteria for detecting infection in vaccinated people, as alleged in OffGuardian article

An article published on 18 May 2021 claimed that the U.S. Centers for Disease Control and Prevention (CDC) changed COVID-19 test criteria to reduce vaccine breakthrough cases and make it seem as if COVID-19 vaccines work, while inflating cases in the unvaccinated. The article was published by OffGuardian, a website that published false information in the past.

The original OffGuardian article received more than 4,000 interactions on Facebook and more than 2,100 interactions on Reddit to date. The article received much more online engagement through being republished by other websites that also publish conspiracy theories, such as Zero Hedge and Gateway Pundit. The copy on Zero Hedge received more than 27,000 interactions on Facebook.

This claim also appeared elsewhere, with some social media users promoting the idea that the CDC was moving the goalposts for vaccinated people to make it harder to detect vaccine breakthrough cases, as can be seen in this Instagram post.

The CDC didn’t change the Ct value for samples from vaccinated people

Vaccine breakthrough cases occur when a vaccinated person becomes infected. While the vaccines are highly effective at preventing disease, no vaccine is 100% effective. Infections in vaccinated people are also detected using the PCR test.

The PCR test detects the presence of the virus by amplifying a small part of the virus’ genetic material. The number of amplification cycles needed to arrive at a level considered to be a “positive” result is also called the cycle threshold (Ct) value. The Ct value depends on the quantity of virus in a sample. The more virus present, the fewer amplification cycles are needed to reach the level for a positive result, while a low viral load requires more amplification cycles to reach that same level.

As evidence for its claim that the U.S. CDC is “lowering their CT value when testing samples from suspected ‘breakthrough infections’” to “decrease the number of ‘breakthrough infections’ being officially recorded”, the article cited this statement on the CDC website:

“For cases with a known RT-PCR cycle threshold (Ct) value, submit only specimens with Ct value ≤28 to CDC for sequencing. (Sequencing is not feasible with higher Ct values.)”

This is a grossly inaccurate interpretation of the CDC guidance. The guidance applies to samples sent for genomic sequencing, which is a technique used to obtain the genetic sequence of the virus. This technique allows scientists to determine the virus’ lineage and identify variants and provides scientists with important information on how the virus is evolving and how mutations change the way the virus behaves. This information in turn helps to guide public health measures and vaccine development.

As is evident from the statement, the CDC didn’t alter the cycle threshold value for the PCR test used to identify presence of infection. The statement is relevant to genomic sequencing, which is an additional test used on samples that already tested positive for SARS-CoV-2 by PCR. The reason why this guidance is in place is because genomic sequencing requires a relatively large amount of the virus’ genetic material in the sample. Therefore, a sample with only trace amounts of the virus’ genetic material, which would show a high Ct value, wouldn’t be suitable for sequencing.

Not sequencing a sample doesn’t change the fact that someone tested positive for COVID-19 by PCR, meaning that the person is infected, making them a COVID-19 case. Therefore, this CDC guidance has no influence on the number of COVID-19 cases recorded, as the article claimed.

Cases from vaccinated people are still being recorded, even if asymptomatic or mild

The article claimed that “asymptomatic or mild infections will no longer be recorded as [COVID-19 cases]”, citing the CDC again:

“As of May 1, 2021, CDC transitioned from monitoring all reported vaccine breakthrough cases to focus on identifying and investigating only hospitalized or fatal cases due to any cause. This shift will help maximize the quality of the data collected on cases of greatest clinical and public health importance. Previous case counts, which were last updated on April 26, 2021, are available for reference only and will not be updated moving forward.”

An Associated Press fact-check explained that this isn’t accurate:

“COVID-19 is a reportable condition, meaning that by law every positive test must be reported. The National Notifiable Diseases Surveillance System requires testing sites and medical facilities to report positive tests to the local health department. They then pass the information to the state health department, which notifies the CDC.”

Kristen Nordlund, a health communications specialist at the CDC, clarified that vaccine breakthrough cases will still be recorded, saying, “CDC is not going to stop reporting cases of COVID-19 in any fashion”.

What it does mean is that, going forward, the CDC won’t publish cases of mild and asymptomatic COVID-19 vaccine breakthrough cases on their website. The AP fact-check:

“However, mild and asymptomatic COVID-19 breakthrough cases, which occur after someone has been fully vaccinated, will no longer be published separately on the CDC’s website. According to the CDC, special surveillance of breakthrough cases was initially set up to identify patterns among individuals who were vaccinated and still got COVID-19. Since an analysis of those cases has not shown any unexpected patterns, the CDC has changed their approach to surveillance.”

Nordlund told AP that “CDC and state health departments will be focusing only on investigating vaccine breakthrough cases that result in hospitalization or death […] Every breakthrough case of COVID will still be reported. We just won’t call it out in a certain place on the website”.

The website also explains that the CDC is recording vaccine breakthrough cases in a separate database for the time being:

“CDC developed a national COVID-19 vaccine breakthrough REDCap database where designated state health department investigators can enter, store, and manage data for cases in their jurisdiction. State health departments have full access to data for cases reported from their jurisdiction.

Ultimately, CDC will use the National Notifiable Diseases Surveillance System (NNDSS) to identify vaccine breakthrough cases. Once CDC has confirmed that a state can report vaccination history data to NNDSS, CDC will identify vaccine breakthrough cases through that system.”

As demonstrated above, the article once again misinterpreted the CDC’s statements. The citation it used to support the claim explained that only fatal or hospitalized cases would be monitored and investigated further. However, this doesn’t mean that mild or asymptomatic cases aren’t reported. As stated above, COVID-19 is a reportable disease by law, therefore all cases need to be reported, regardless of the severity or vaccination status. But only reported cases that are severe are monitored and investigated.

COVID-19 vaccines are highly effective at preventing severe COVID-19 and death; they aren’t “experimental gene therapy”

The article claimed that the CDC was moving the goalposts for PCR testing in order to make it seem as if “the experimental gene-therapy ‘vaccines’ are effective at preventing” COVID-19.

This claim is inaccurate and poorly reasoned. Firstly, scientists already had a pool of evidence demonstrating that the COVID-19 vaccines are effective at preventing disease, predating the alleged change in PCR cycle thresholds in May 2021.

This evidence comes from the clinical trials examining the COVID-19 vaccines authorized by the U.S. Food and Drug Administration (FDA), which demonstrated that the vaccines are highly effective at preventing severe COVID-19. In November 2020, Pfizer and BioNTech reported that the vaccine has 95% efficacy at preventing symptomatic COVID-19, while Moderna reported 94% efficacy. Johnson and Johnson reported that their vaccine has 85% efficacy at preventing severe illness.

In addition, real-world evidence from ongoing vaccination campaigns, also predating the alleged change, demonstrated that the vaccines are highly effective at protecting people from severe disease and death, as seen in this CDC study on the Pfizer-BioNTech and Moderna RNA vaccines, conducted between December 2020 and April 2021^[1], as well as this study in Israel conducted between January and April 2021, published in The Lancet^[2].

In other words, there was already reliable evidence showing that the vaccines are effective, without having to resort to the alleged change in PCR test methodology. Had the vaccines not worked, this would have been evident during clinical trials and the vaccines wouldn’t have received emergency use authorization by the FDA.

Thirdly, COVID-19 vaccines are neither “experimental” nor “gene therapy”. Their effectiveness and safety was demonstrated during clinical trials before being released to the public. Gene therapy involves the modification of a person’s genes to treat disease. COVID-19 vaccines cannot modify DNA, as previously explained by Health Feedback, thus disqualifying them as “gene therapy”.

PCR tests detect infection, but not necessarily contagiousness; most positive tests are true positives

The article brought up inaccurate and misleading claims dating back last year to at least November 2020, specifically that the COVID-19 PCR test is overly sensitive and inflates the number of COVID-19 cases. These claims were reviewed by Health Feedback and found to be inaccurate (see here and here).

As explained in our previous reviews, the claim is based on a misinterpretation of scientists’ statements, including that of the director of the U.S. National Institute of Allergy and Infectious Diseases Anthony Fauci. The scientists discussed concerns about the issue of positive PCR tests with high Ct values, namely that many people with such results may no longer be infectious.

This issue calls into question whether PCR tests are a practical way of informing a person infected with COVID-19 of what steps they should take after their diagnosis, specifically whether they should self-isolate. This consideration is also relevant to helping public health authorities determine whether contact tracing for that individual is needed.

However, some wrongly took these concerns to mean that PCR tests produce many false-positive results. Whether one has a high or low Ct determines whether contact tracing and self-isolation measures would be useful. This is because high viral load (low Ct value) likely indicates that a person is infectious, whereas a low viral load (high Ct value) likely indicates that a person is not infectious or has low transmissibility.

However, being infected isn’t the same as being contagious. It is inaccurate to label high Ct positive results as “false positives”. The term “false positive” indicates that a person tested positive but doesn’t have the infection^[3]. However, a person is or has been infected if they test positive, regardless of whether the test had a high or low Ct value. This also means that a person with a positive result and high Ct value would correctly be classified as a COVID-19 case.

The sensitivity of the PCR test is not responsible for the high number of COVID-19 cases worldwide, which led to the declaration of a pandemic. Simply put, the detected number of COVID-19 cases are high because there are many infected people. The claim fails to distinguish between the test’s ability to confirm an infection—which is what case numbers measure—with the test’s ability to determine contagiousness.

REFERENCES

• 1 – Thompson et al. (2021) Interim Estimates of Vaccine Effectiveness of BNT162b2 and mRNA-1273 COVID-19 Vaccines in Preventing SARS-CoV-2 Infection Among Health Care Personnel, First Responders, and Other Essential and Frontline Workers — Eight U.S. Locations, December 2020–March 2021. Mortality and Morbidity Weekly Report.
• 2 – Haas et al. (2021) Impact and effectiveness of mRNA BNT162b2 vaccine against SARS-CoV-2 infections and COVID-19 cases, hospitalisations, and deaths following a nationwide vaccination campaign in Israel: an observational study using national surveillance data. The Lancet.
• 3 – Lalkhen et al. (2008) Clinical tests: sensitivity and specificity. Continuing Education in Anaesthesia Critical Care & Pain.