the peak in test positivity occurring in early January 2020 ( Figure 2 ). Influenza cases fell sharply in early 2020 , dropping to only a small number of sporadic cases as COVID emerged in March 2020 ( Figure 3 ). Small numbers of influenza cases continued through the earliest phase of the pandemic . Test positivity rates for influenza were slightly higher than those for SARS- CoV-2 during this period lasting through September 2020 ( 5.1 % vs . 6.7 %, < 0.001 ), a difference explained by the high positivity rate seen in March 2020 as the 2019 / 2020 influenza season subsided . There was a significant negative correlation between the number of positive tests for SARS-CoV-2 and influenza during this period ( -0.18 , p = 0.006 ).
The next period from November 2020 through January 2021 included a large number of COVID-19 cases ( 11,709 ), predominantly of the B . 1.2 variant and only a few influenza cases ( 50 ). Test positivity rates for SARS-CoV-2 were now much higher than for influenza ( 16.3 % vs . 0.36 %, p < 0.0001 ). A small number of influenza cases continued through June 2021 . SARS- CoV-2 test positivity was lower than that seen during the preceding surge and was made up of first epsilon and then the alpha variant . There was no correlation between positive test numbers for the viruses because of the small number of positive influenza tests .
Emergence of the delta variant in WV was associated with a high test positivity rate for SARS-CoV-2 ( 15.5 %) from August 2021 through October 2021 . During this period , there were essentially no positive influenza tests ( 2 positives of 18,644 tests , 0.01 % positive ). Influenza cases then increased in December 2021 . At the same time , SARS- CoV-2 mutated to the omicron BA . 1 variant . This variant was highly transmissible as shown by the SARS-CoV-2 positivity rate of 22.7 % from December 2021 through March 2022 . The influenza test positivity rate was 3.0 % during this period when seasonal influenza is expected to peak in WV . The transition to the omicron BA . 2 variant during April 2022 was associated with a low SARS-CoV-2 positivity rate ( 11.4 %), while influenza cases persisted with a test positivity rate stable at 3.1 %. Again , there was no correlation between positive test numbers for the viruses because influenza positive tests remained low .
The COVID-19 pandemic did not appreciably alter the number of influenza tests performed until the 2021 / 2022 season ( Figure 4 ). The average number of influenza tests performed per day for threemonth periods from January through March of the 2018 / 2019 , 2019 / 2020 , and 2020 / 2021 seasons were 159 , 216 , and 166 tests , respectively . Testing for influenza
FIGURE 3 : Average ( 7-day moving ) number of positive tests for SARS-CoV-2 and influenza from December 2019 through June 2022 .
West Virginia Medical Journal • June 2023 • 25