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Is it COVID-19 or is it flu?

Covid - Flu

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As the influenza season arrives in the Northern Hemisphere, at least three things are clear:


One reason it is so important to differentiate influenza and COVID-19 is to conserve a limited supply of resources, including remdesivir. The drug has been shown to be more effective than a placebo in treating severe and moderate COVID-19, but its use to treat influenza would be a waste of resources.



A perfect storm?

Many questions remain unanswered about the interaction of COVID-19 and influenza in the body. Researchers missed opportunities to conduct studies this spring, as the pandemic surged in the Northern Hemisphere

  just as flu season was flaming out. But looking ahead to the 2020-2021 flu season, some researchers fear the worst, knowing that many viruses work together, teaming up to co-infect hosts and neutralize antiviral immune procedures.

Scientists in Berlin and Paris used a mathematical model to study the first months of the corona pandemic in Europe. The model suggests that the decrease of COVID-19 cases in spring was not only related to countermeasures (e.g., social distancing), but also to the end of the flu season. Those findings suggest influenza may have increased transmission of the coronavirus by an average of 2.5-fold. If so, the upcoming flu epidemic could have an amplifying impact on the COVID-19 pandemic.

Meanwhile, a retrospective study from China showed that coinfection of influenza and COVID-19 was a significant risk factor for prolonged hospital stay. Researchers found that COVID-19 patients who were coinfected with influenza shed SARS-CoV-2 longer than other COVID-19 patients (17 days vs 12 days on average), though the reason is unknown.

If there is a bright spot, it is this: Precautionary measures related to COVID-19, such as social distancing and mask-wearing, could control the incidence of flu as well as COVID-19 in the 2020-2021 flu season. Influenza viruses and SARS-CoV-2 predominantly spread via respiratory droplets that are transmitted during close community contact. Consequently, social distancing policies designed to limit COVID-19 transmission are also effective against influenza. Studies from the U.S. Centers for Disease Control and Prevention and World Health Organization demonstrate a similar effect in the United States, Australia, Chile and South Africa


Is it COVID or is it the flu?

One reason it is so important to differentiate influenza and COVID-19 is to conserve a limited supply of resources, including remdesivir. The drug has been shown to be more effective than a placebo in treating severe and moderate COVID-19, but its use to treat influenza would be a waste of resources.

A second reason is that efforts to mitigate flu and COVID-19 differ from each other. For example, the drug corticosteroid dexamethasone appears to be effective in some patients hospitalized with COVID-19, but is potentially harmful to those with influenza A. Further, without knowing which virus is at work, people with COVID-19 during flu season might mistakenly attribute their symptoms to influenza and avoid taking precautions to prevent spreading SARS-CoV-2, Michael Osterholm, PhD, MPH, of University of Minnesota’s Center for Infectious Disease Research and Policy, was quoted as saying in an interview.


Patients’ physical symptoms alone won’t always tell healthcare providers whether they are dealing with influenza or COVID-19. The two viruses share some of the same symptoms, including fever, cough, shortness of breath, fatigue, sore throat muscle pain, runny or stuffy nose and headaches. However there are some key differences such as new loss of smell/taste. Lab tests are essential in successful diagnosis.



With worldwide manufacturing facilities and an international sales and distribution network, SEKISUI Diagnostics offers a line of CLIA-waived point-of-care tests to help identify influenza virus A and B.



In September 2020, the European Centre for Disease Prevention and Control (ECDC) produced a report to provide guidance on COVID-19 strategies and objectives. They highlighted several key messages, including implementing objective driven and sustainable testing in order to support the public health response to the pandemic in order to mitigate its impact on vulnerable populations and healthcare systems.  Also included in the report was the recommendation that patients admitted to hospital with acute respiratory symptoms, as well as those from sentinel primary care surveillance should be tested for both SARS-CoV-2 and influenza. This recommendation is to support clinical decision making, as well as inform infection prevention and control measures.


The United States has developed a test -- the CDC Influenza SARS-CoV-2 (Flu SC2) Multiplex Assay -- to detect and differentiate flu and COVID-19. But it is only available at public health laboratories, not the physician’s office. Meanwhile, Oxford Nanopore is developing LamPORE to test for multiple pathogens within a single sample, including influenza A (H1N1 and H3N2), influenza B, respiratory syncytial virus (RSV) and SARS-CoV-2.


Get your flu shot!

Meanwhile, as the Pfizer-BioNTech COVID-19 vaccine is being deployed, medical and public health professionals advise people to get their flu shots now. Mitigating the overall burden of respiratory disease is particularly important for older adults who have increased susceptibility to both influenza and COVID-19.

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Keith A. Nichols

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