virus replication while coronaviruses only caused a minimal inhibition of influenza . 11 In vitro studies support the premise that SARS-CoV-2 can be inhibited by previous infection with influenza but not by concurrent or secondary infection ; whether SARS-CoV-2 can inhibit secondary infection by influenza remains unclear based on published studies . 12 , 13 The negative correlation found in our study between SARS-CoV-2 and influenza suggest an interaction between the viruses ; however , the large difference in prevalence precludes definitive conclusions .
The low incidence of co-positivity for both viruses seen in our study also suggests viral interference . Overall , 0.4 % of those in our study who were positive for SARS- CoV-2 were also positive for influenza A . This result is similar to other studies finding less than 1 % of COVID-19 infections having a co-infection with influenza . 14-16 This low rate of co-infection is consistent with the viral interference studies discussed above , as after primary infection it is difficult for a second infection to occur . Although coinfection is rare , it does seem to increase the risk of severe disease . 17 The low incidence of co-positivity for both viruses may also support a decision to not test a patient for influenza if they are known to be positive for SARS-CoV-2 and vice versa .
We acknowledge the limitations of our study , including its retrospective nature . Many individuals who were infected with SARS-CoV-2 may not have been co-tested with influenza and are not represented by this study . The data may not capture the true extent of COVID-19 cases at the pandemic onset because SARS-CoV-2 testing was extremely limited . As our data only includes individuals who sought testing at healthcare facilities , it does not capture individuals who performed at-home testing . Self-testing became more common as the pandemic progressed ; thus , a significant portion of people who tested positive for SARS-CoV-2 at home may not be included . It remains unclear if our findings can be generalized to other populations that are less rural than WV . Also , since our study focused on tests performed and not individuals , there is a chance that one individual could have participated in multiple testings , and the effect of this possible scenario on data outcomes is difficult to predict .
CONCLUSION
The COVID-19 pandemic disrupted the normal seasonal patterns of influenza infection in WV . More studies are needed to better understand factors that influence viral spread in rural states like WV and how the emergence of SARS-CoV-2 and other novel viruses can affect seasonal respiratory disease ( including respiratory syncytial virus [ RSV ]). Our study was conducted before the surge in RSV cases in fall 2022 .
FUNDING
This study was partially funded by the WV Department of Health & Human Resources .
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