Claim that flu shot causes false positive results on COVID-19 tests is unsupported and misleading

Key takeaway

The 2012 study cited in this claim only tested for coronaviruses that cause the common cold, but not COVID-19, which was not discovered until 2019. Furthermore, only one of 69 individuals who had received the flu shot tested positive for coronavirus—a frequency that precludes drawing a causal association between the flu shot and coronavirus detection.

Reviewed content

Verdict:

Incorrect

Claim:

The flu shot causes false positive results on COVID-19 tests

Verdict detail

Imprecise: The study cited in support of this claim only tested samples for coronaviruses that cause the common cold. Although these belong to the same family as the virus that causes COVID-19, they do not cause the same type of illness.
Flawed reasoning: The study was published in 2012, long before the novel coronavirus was discovered in 2019 and diagnostic tests began to be developed.
Inaccurate: The flu shot contains inactivated (dead) influenza virus, not any strain of coronavirus.

See our method of evaluation

Full Claim

The flu shot causes false positive results on COVID-19 tests; the flu shot is responsible for COVID-19 deaths

This claim has been published in several Facebook posts, often accompanied by a table from a 2012 study by Cowling et al. published in Clinical Infectious Diseases^[1], and has been viewed more than 280,000 times since 21 March 2020. In addition, these posts have become the foundation for the claim that the flu vaccine is responsible for COVID-19 deaths.

The study examined the incidence of non-influenza respiratory viruses in children who had received the trivalent flu vaccine (TIV) and compared it with that of children who had not received TIV, using variants of the polymerase chain reaction (PCR) technique, namely reverse transcription PCR (RT-PCR) and multiplex PCR. The table in the Cowling study can be found here.

According to the study’s Methods section, RT-PCR was used to detect influenza viruses, while the multiplex PCR test was used to detect 19 respiratory viruses, including coronaviruses types NL63, HKU1, 229E, and OC43. These are coronaviruses that cause the common cold, as the U.S. Centers for Disease Control and Prevention (CDC) explain. Although these virus strains belong to the coronavirus family, just like the viruses that cause COVID-19, severe acute respiratory syndrome (SARS), and Middle East respiratory syndrome (MERS), they do not cause the same types of illness.

It is also important to keep in mind the timeline of events. SARS-CoV-2, the causative agent for COVID-19, was first identified in 2019^[2,3], whereas the study was published in 2012. It would have been impossible for the multiplex PCR used in the study to detect a virus that was unknown and possibly even non-existent at that time.

Detecting coronavirus in individuals who received the flu shot does not mean that the flu shot caused the detection of coronavirus. There is no plausible biological link between the two, as the flu shot only contains inactivated (dead) influenza virus. In fact, the table from the Cowling study shows that of the 69 TIV recipients, only one tested positive for coronavirus. This single case is insufficient to draw any causal association between the flu shot and coronavirus detection.

Overall, it is misleading to claim that this study’s results can be reliably extrapolated from the common cold viruses detected to the coronavirus that causes COVID-19. No evidence supports the claim that the flu shot resulted in false positives or that the flu shot caused COVID-19 deaths.

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The 2012 study has also been used to claim that the flu vaccine increases the risk of coronavirus infections. There is no evidence supporting this assertion, as explained in Health Feedback’s earlier review. See a list of all coronavirus-related reviews written by Health Feedback here.

Health Feedback is working with the CoronaVirusFacts Alliance, a coalition of more than 100 fact-checkers who are fighting misinformation related to the COVID-19 pandemic. Learn more about the alliance here.

REFERENCES

• 1 – Cowling et al. (2012) Increased Risk of Noninfluenza Respiratory Virus Infections Associated With Receipt of Inactivated Influenza Vaccine. Clinical Infectious Diseases.
• 2 – Zhu et al. (2020) A Novel Coronavirus from Patients with Pneumonia in China, 2019. New England Journal of Medicine.
• 3 – Lu et al. (2020) Genomic characterisation and epidemiology of 2019 novel coronavirus: implications for virus origins and receptor binding. The Lancet.