Some 136 people were hospitalized for the flu between Oct. 1, 2020, and Jan. 16, 2021, and there were 292 deaths involving influenza during that period, the CDC reported. One child has died.
The flu season is far from over — it usually begins in the fall, and peaks between December and February.
But in comparison, 400,000 people were hospitalized for the flu and 22,000 died, including 434 children, during the entire 2019–2020 season, which the CDC described as “severe” for kids 4 years old and younger, and for adults 18-49 years old.
During the months preceding the surge of SARS-CoV-2 infections this fall and winter, many public health officials expressed concern about the potential for a “double-barreled” respiratory virus season. In this scenario, healthcare facilities would be totally overwhelmed by: 1) patients afflicted by infections caused by endemic respiratory viruses (such as influenza) that occur during any normal year, and 2) a massive influx of coronavirus patients. Fortunately, such a catastrophe did not come to pass. The reason for this is an unprecedented reduction in flu prevalence for the 2020–21 season.
So perhaps a biological process, whereby viruses engage in some form of competition, or interactions, can better explain disappearances such as those currently being observed.
Subsequent research has borne out real world examples related to the phenomenon described by Simpson. According to a group of researchers at Yale, it is likely that a 2009 autumn rhinovirus epidemic interrupted the spread of influenza. The authors of that study write: “one respiratory virus can block infection with another through stimulation of antiviral defenses in the airway mucosa”. Results from another study, conducted in mice, support those findings. Mice were infected with either a rhinovirus or a murine coronavirus, and it was found that both attenuated influenza disease. Moreover, it was observed that the murine coronavirus infection reduced early replication of the influenza virus. In another study, negative interactions between noninfluenza and influenza viruses were suggested. According to the authors: “when multiple pathogens cocirculate this can lead to competitive or cooperative forms of pathogen–pathogen interactions. It is believed that such interactions occur among cold and flu viruses”. A recently published study examining the effects of interactions between an adenovirus and influenza in mice suggested that certain respiratory infections could impede “other viruses’ activities within the respiratory tract without attacking unrelated viruses directly”. Finally, in a paper entitled “A systematic approach to virus–virus interactions”, the authors state: “increasing evidence suggests that virus–virus interactions are common and may be critical to understanding viral pathogenesis”.