I have often heard COVID-19 compared to influenza, particularly when there is intent to question our collective actions. Social distancing, school closures, limited mobility, handwashing and use of facemasks impose a cost on all of us. Influenza is familiar and—to many—an easy comparator. Like SARS-CoV-2, it is a respiratory virus that contributes to significant morbidity and mortality on a yearly basis. As a researcher who has studied influenza in primary care and community settings for the past quarter century, however, I can attest SARS-CoV-2 is not like influenza. I respect influenza; SARS-CoV-2 scares me.
Today, as the U.S. has surpassed 1,000,000 cases of COVID-19 and we have tallied nearly 60,000 deaths, I provide a simple graphic for PracticeUpdate readers to ponder. The Influenza Branch at CDC has long used the Pneumonia and Influenza Mortality Index to gauge influenza’s passage. The index is based on the percentage of all deaths occurring in the U.S. that have pneumonia or influenza listed as a cause of death during a given week. A seasonal baseline is calculated as well as an “epidemic threshold.” When the P&I death percentage exceeds the threshold, we are seeing the excess of deaths that are typically related to influenza. Of late, deaths due to COVID-19 have been added to the equation… and that is where the similarities end. We recently hit an all-time high of 23.5%. Nearly one quarter of Americans who died during the week ending on April 11, died of pneumonia, influenza or COVID-19 (and influenza was no longer in circulation). This compares to the 2009 influenza A(H1N1) pandemic’s P&I peak of 8.1%. January 2018 also witnessed a very bad outbreak of influenza and registered 10.8%.
Like SARS-CoV-2, influenza can be controlled by social distancing, school closures, limited mobility, handwashing and use of facemasks. But, we also have ample testing capacity, vaccines and antiviral medications. Until we have good means for prevention, diagnosis, treatment and control of SARS-CoV-2, I advise caution in making too many easy comparisons.