Interplay of Influenza A/B Subtypes and COVID-19

Influenza, or most commonly termed the flu, is a common respiratory illness caused by viral infection. The circulation of this virus is found year-round but is more common during the flu season: fall and winter. In the United States, the number of reported cases begins to rise in October, reaches a peak in December, and returns to normal in April. Even though there are four subtypes of the Influenza virus, the seasonal flu outbreaks in humans are caused by type A and B viruses. eVision utilizes influenza data provided by the United States Center for Disease Control and Prevention (CDC) and the World Health Organization (WHO) to analyze influenza A and B cases throughout the flu season. During the 2019–20 flu season, the positive influenza cases reported in the US were between 36 and 56 million, which is the highest over the past six years. However, during the 2020–21 flu season which is the first complete flu season within the COVID-19 pandemic, the reported flu cases reduced drastically to 1,899; of which 713 were caused by influenza A viruses, and 1,186 by influenza B viruses. This indicates that the number of flu B cases was higher than that of flu A which was not normally the case prior to the COVID-19 pandemic. It was further observed that flu B reached its peak either at the same time or earlier than flu A which is also unusual compared to the flu trends prior to the onset of the COVID-19 pandemic. This peculiar trend is also noted during the Severe Acute Respiratory Syndrome (SARS) outbreak in 2003. This paper reports the findings on deviation in the Influenza type A and type B trends during the circulation of Coronavirus in the US and Canada and provides possible reasons for these changes.