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September 12, 2023

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Influenza Season 2023-2024: An Early Look

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On behalf of the TeamHealth Emerging Infectious Disease Task Force


It’s late summer, early fall – a magical time of the year when the thoughts of epidemiologists turn to influenza. Predictions of upcoming influenza seasons are difficult in the best of times. Such predictions are now more challenging due to the impacts of the pandemic. The once stable seasonal patterns of respiratory viruses have been disrupted by SARS-CoV-2.

The Continued Impacts of SARS-CoV-2 on Influenza

The SARS-CoV-2 virus continues to co-circulate with the influenza virus globally. Although the level of circulating SARS-CoV-2 virus is still quite high, it is nowhere near the levels seen during the more intense phases of the pandemic.

At the time this post is being written, COVID-19 admissions nationally have increased threefold over the last 30 days. In the southern segments of the nation – particularly Florida – COVID-19 admissions have increased over fivefold in many locations.

Indicators Monitoring COVID-19 Transmission

The EDIT monitors five primary indicators that have an impact on SARS-CoV-2 transmission. These indicators help one understand if virial transmission is being inhibited or promoted. These include:

  1. Congregating together (School restarting, heat forcing people inside with circulated dry air)
  2. Public awareness (With the removal of the Public Health Emergency most individuals are complacent regarding COVID-19.)
  3. Public health precautions (Social distancing, masking, hand washing, respiratory etiquette is all at very low levels currently.)
  4. Travel (Intermingling – some increase currently but significant increases coming in about two months from holiday surges)
  5. Vaccine protection (Currently most people are at or approaching a vaccine nadir from their initial series or last booster. There is also a decline in overall booster recommendation compliance, and a decrease in vaccine effectiveness against infection due to emerging variants. Protection against serious disease however still remains fairly high depending on the age strata and co-morbidities.)

There are obviously other important indicators, but these five are fairly easy to measure and monitor.

Utility of the Southern Hemisphere Influenza Season

As we have noted in previous posts, influenza activity in the Southern Hemisphere precedes the Northern Hemisphere flu season. The nation of Australia is usually the most prescient of any nation regarding the coming flu season in the United States.

The Southern Hemisphere season can provide us with information about likely influenza strains, disease burden, antiviral sensitivity, vaccine effectiveness and intensity of the upcoming Northern flu season.

What’s Going on with the Southern Influenza Season?

Analysis of Australian influenza and other Southern Hemisphere nations or regions thus far indicates that there are obvious spikes in influenza-like-illness (ILI) being seen.

The ILI cases in Australia and a few other southern locations have been slightly more intense than typical. Although this has caused some nations to classify their influenza season as “severe” – none of these locations have had overwhelming surges on the medical infrastructure. And, there have been no “surprisingly” dangerous or unexpected impacts from influenza.

Projections for Influenza 2023-2024 Season: Onset and Peaks

The onset of the 2023-2024 influenza season is likely to be earlier by four to six weeks than in historic seasons. With this onset, the peak of the season regarding cases and admissions should be during late December 2023 or early January 2024. However, the current rapid rise in COVID-19 cases makes this projection less reliable.

Influenza Vaccine Selection and Antivirals

The vaccines created last year should be effective for the upcoming year as well. Sufficient stocks of vaccines are available. The antiviral medications for influenza should also be effective against the likely circulating strains.

When to Vaccinate for Influenza?

The consensus recommendations are that vaccination for influenza should begin in mid-August 2023 – as soon as the vaccines are available – and that most vaccination of the public should be completed by late October 2023.

As always, more information is available in the References and Resources for this post.

References and Resources

Australian Government: Department of Health and Aged Care. Influenza surveillance program. (HERE)

Bouffanais R, Lim SS. Cities – try to predict superspreading hotspots for COVID-19. Nature. 2020;583(7816):352-355. (HERE).

CDC. FLUview. Weekly U.S. Influenza Surveillance Report. (HERE)