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    1. Disease
    2. Flu

    COVID-19 and influenza epidemics this winter?

    Oct. 19, 2022
    Photo 207314212 © Pop Nukoonrat | Dreamstime.com
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    On January 31, 2020, the Secretary of the U.S. Department of Health & Human Services (HHS) declared a Public Health Emergency followed by the declaration of a National Emergency by the President of the United States.1,2 Congress granted $25 billion to HHS to take immediate steps to prepare for the advancing COVID-19 pandemic, and soon thereafter, the National Institutes of Health (NIH) created the Rapid Acceleration of Diagnostics Initiative (RADx)3 whose task, as implied, was to accelerate the delivery of diagnostic tests to healthcare facilities and laboratories across the nation. Tremendous progress was achieved in record time, including the creation of effective vaccines, advancing the development of therapeutic agents, and the launch of new antigen and molecular diagnostic tests for the detection of SARS-CoV-2 — all in less than one year. These efforts continue with lessons learned, advancing technologies, and emerging needs.

    As the pandemic spread quickly around the world, there were very few options to protect the public from widespread infection and serious disease in the beginning months. Nonpharmaceutical interventions (NPI) were introduced rapidly and promoted widely across the United States. Reduced hospitalizations and deaths were observed in locations where lockdowns, school closures, social distancing, mask-wearing, and work-from-home programs were common.4,5 This protection by NPI, although not absolute, provided HHS and partnering industries the time needed to take steps to address the emergency.

    Possible linkage of nonpharmaceutical interventions to influenza

    However, the impact of NPI was not limited to the spread of SARS-CoV-2. These measures also profoundly affected the incidence of other respiratory diseases, including influenza.6 Figure 1 shows the course of influenza infections in the United States from September 2019 to the present.7 At the end of the 2019–2020 season, when NPI was introduced broadly In the United States, there followed 18 months during which the influenza positivity rates rarely exceeded even 2%, as reported to the Centers for Disease Control and Prevention (CDC). Subsequently, the 2021–2022 respiratory season saw two influenza surges spanning from mid-November 2021 to April 2022. Both surges failed to achieve the higher positivity rates encountered in more “typical” influenza epidemic seasons when positivity rates often exceed 25% nationally.7

    Figure 1. USA influenza status 2019 week 40 to 2022 week 35.
    Figure 1. USA influenza status 2019 week 40 to 2022 week 35.
    Both influenza surges overlapped with the arrivals of the Omicron variant in early December 2021 and its subvariants, BA.4 and BA.5, after the new year, spanning the same period from December 2021 to April 2022 and beyond.7 It is possible that public announcements about the rapid increase in COVID-19 cases and deaths (see Figure 2) stimulated a renewed enthusiasm for using NPI, thereby also mitigating the influenza surges. This and other rationales are open to debate and certainly more research.8
    Figure 2. Number of U.S. COVID-19 cases and deaths reported to CDC December 1, 2021 to April 1, 2022.
    Figure 2. Number of U.S. COVID-19 cases and deaths reported to CDC December 1, 2021 to April 1, 2022.
    Whatever the explanations, the CDC has reported that between October 2021 and June 11, 2022, there were 8 million to 13 million confirmed influenza cases; 82,000 to 170,000 hospitalizations; and 5,000 to 14,000 influenza-associated deaths In the United States.9 What do these observations portend for this year’s flu season? Epidemiologists have often looked to the southern hemisphere, particularly Australia, for clues about what we might expect in the northern hemisphere (especially for influenza).
    Figure 3. Laboratory-confirmed influenza cases in Australia January 2017 to August 28, 2022.
    Figure 3. Laboratory-confirmed influenza cases in Australia January 2017 to August 28, 2022.
    As shown in Figure 3, Australia’s 2020 and 2021 seasons were profoundly suppressed with exceptionally low numbers of cases, hospitalizations, and nearly no deaths.10 These drops are attributed mainly to the broad implementation of NPI nationwide.11 Unlike the United States, Australia had no influenza surges detected in their first or second year of COVID-19. However, Australia’s 2022 influenza season resulted in its worst influenza outbreak in the country’s recent history. Such events in the southern hemisphere are not absolute predictors of events in the northern hemisphere, but they raise concern for this winter in North America. The factors discussed in Table 1 augment this concern.
    Table 1. Factors that suggest a significant COVID-19 and influenza winter season are approaching.
    Table 1. Factors that suggest a significant COVID-19 and influenza winter season are approaching.

    Predictions for 2022–2023

    Many epidemiologists agree that a combination of both a new COVID-19 surge and a true influenza epidemic winter season in the United States is now likely. The use of NPI was likely strong enough to slow or halt this past winter’s surges, but this may not be the case this year, given the exhaustion of our populace, the low vaccination rates, the reopening of schools, the return to workplaces, the ongoing decline in NPI use, and the overall diminution of herd immunity, as discussed above.

    Staying ahead through testing

    The signs and symptoms for infections by SARS-CoV-2 and influenza are very similar, precluding their reliable diagnosis based on symptoms alone.28 Therefore, it seems likely that in many cases, if both COVID-19 and influenza are circulating in a community, as clearly occurred last winter, then physicians will likely want to test for all three viruses — SARS-CoV-2 and influenza (Types A and B) — at the same time.

    There are currently 277 molecular and 51 rapid antigen tests with emergency use authorizations (EUAs) available for diagnosis of SARS-CoV-2 in the United States. Among these are nine multiplex molecular tests and three multiplex antigen tests for assessment of SARS-CoV-2 and influenza.29,30 Additional multiplex tests will likely receive EUAs soon. Their use of one specimen type, less hands-on time, and improved turnaround time offer advantages to laboratories, physicians, and patients — especially those who are considered high-risk and may benefit from timely therapeutic intervention.31

    REFERENCES

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    10. Australian Government Department of Health. Australian influenza surveillance report – no. 11 – fortnight ending 28 August 2022. Published online 2022. Accessed September 26, 2022. https://www1.health.gov.au/internet/main/publishing.nsf/Content/ozflu-surveil-no11-22.htm.
    11. Milazzo A, Giles L, Parent N, et al. The impact of non-pharmaceutical interventions on COVID-19 cases in South Australia and Victoria. Aust N Z J Public Health. 2022;46(4):482-487. doi: 10.1111/1753-6405.13249.
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    25. Krauland MG, Galloway DD, Raviotta JM, et al. Agent-based investigation of the impact of low rates of influenza on next season influenza infections. bioRxiv. Published online 2021:2021.08.18.21262185. doi:10.1101/2021.08.18.21262185.
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