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CSL Seqirus Presents Real-World Evidence at ESWI Demonstrating the Impact of Influenza Vaccination Campaigns to Help Protect People and Healthcare Systems

• Results from a retrospective cohort study from 2015 to 2020 demonstrated a notable rise with increasing age in pneumonia-related medical encounters following an influenza encounter.1
• Results from a retrospective cohort study during the 2019/20 season demonstrated the benefit of an adjuvanted influenza vaccine in prevention of influenza-related medical encounters among adults 65 years and older.2
• Results from a study across three consecutive influenza seasons showed that vaccination with cell-based influenza vaccines resulted in lower rates of test-confirmed influenza compared with traditional egg-based vaccines.3


CSL Seqirus, a business of CSL (ASX:CSL), today shared new real-world evidence (RWE) studies conducted in the United States, demonstrating the value of influenza vaccination in protecting public health. These data are being presented at oral and poster sessions at the European Scientific Working Group on Influenza (ESWI) Conference taking place in Valencia, from September 17-20, 2023.

One study evaluating the clinical impact of seasonal influenza in adults from 2015 to 2020, revealed a notable rise in pneumonia-related medical encounters with increasing age following an influenza encounter.1 On average about one third of adult patients above 50 years of age who were hospitalized for influenza were diagnosed with pneumonia during their hospitalization.1 

“This finding may be explained by our immune systems beginning to wane as we age, increasing the risk of developing serious flu-related complications,” said Dr. Gregg Sylvester, Chief Health Officer at CSL Seqirus. “It is important to conduct real world studies to evaluate influenza vaccine effectiveness, gathering insights to tailor our ongoing approach to preventing disease and serious flu-related illness, particularly among these vulnerable populations.”

Results from a separate retrospective cohort study during the 2019/20 influenza season demonstrate the clinical benefit of an adjuvanted inactivated trivalent influenza vaccine compared with high-dose inactivated trivalent influenza vaccine in preventing influenza-related medical encounters (IRMEs), outpatient IRMEs, and influenza- or pneumonia-related hospitalizations among adults with cumulative risk factors.2 Results also found comparable effectiveness of these influenza vaccines in individuals with no high-risk conditions.2

In a third study, data from a retrospective test-negative design showed the clinical value of cell-based quadrivalent influenza vaccines (QIVc) compared with traditional egg-based quadrivalent influenza vaccines (QIVe) in preventing outpatient test-confirmed influenza.3 The study was conducted over three consecutive influenza seasons characterized by different circulating influenza viruses and degrees of egg-adaptation and align with previously published QIVc relative effectiveness studies for the same seasons.3 Review of three seasons of real-world data allows for evaluation of trends in the effectiveness of QIVc over time and in the context of season-over-season changes, given the variability of the virus.3  

“Vaccines remain one of our greatest tools for fighting influenza, a disease that continues to result in substantial morbidity and mortality worldwide," said Raja Rajaram, Head of Global Medical Strategy, CSL Seqirus. “At CSL Seqirus, we are committed to advancing the science of influenza prevention, and these studies show the benefits of innovative vaccine technologies, including cell-based and adjuvanted influenza vaccine technology, on reducing the burden of flu."

RWE is a complement to randomized controlled trial (RCT) research, assessing influenza vaccine effectiveness on a continual basis and providing an ever-growing data set on real-world outcomes.


Healthcare Resource Use and Complications Among Adults with an Influenza-Related Medical Encounter: 2015-2020 Influenza Seasons in the United Sates (V118_61RWE)
The U.S. Centers for Disease Control and Prevention (CDC) estimates that influenza infections have resulted in 9–41 million symptomatic illnesses, 140,000–710,000 hospitalizations and 12,000–52,000 deaths annually between 2010 and 2020.1 This study aimed to evaluate healthcare resource use and complications among adults with an influenza-related medical encounter.1

Results from the study, which included between 887,260 and 3,628,168 patients per season, found that the proportion of patients with a pneumonia-related medical encounter within 2 weeks of an index influenza-related outpatient (OP) or emergency-room (ER) visit increased with age.1 

Following an outpatient influenza visit, the mean percentage of pneumonia-related medical encounters was 2.1% for patients 18-49, 3.9% for 50-64, and 6.9% for 65+.1 Following an emergency-room visit, the mean percentage was 4.7% for patients 18-49; 9.0% for 50-64; 14.9% for 65+.1 Compared to other age groups, pneumonia diagnoses among hospitalized influenza patients were most common among patients 50–64 (35.7%).1

Relative Effectiveness of the MF59-Adjuvanted Influenza Vaccine vs High-Dose Influenza Vaccine in Older Adults with Influenza Risk Factors during the 2019-2020 U.S. Influenza Season 
Researchers conducted a retrospective cohort study during the U.S. 2019-20 influenza season during which 1,115,725 (30.3%) patients received aTIV and 2,561,718 (69.7%) received HD-TIV.2 The primary outcome of any IRME for patients with 0 risk factors demonstrated comparability in effectiveness between aTIV and HD-TIV (rVE [95% CI]: 5.2 [-5.9–15.1]).2 For patients with 1-2, ≥3, or ≥1 risk factors aTIV was more effective than HD-TIV (rVEs [95% CI] of 18.4 (13.7–22.9), 10.4 (7.4–13.3), and 12.5 (10.0–15.0), respectively).2 The same trends were observed for the secondary outcomes. 2

Superior Effectiveness of Cell-Based Versus Egg-Based Quadrivalent Influenza Vaccines Against Outpatient Test-Confirmed Influenza Over Three Consecutive Seasons in the United States 
Researchers applied a retrospective test-negative design among individuals aged 4-64 years that were vaccinated against influenza with either QIVc or QIVe and who had an influenza test obtained as part of routine outpatient care within +/- 7 days of a documented acute respiratory or febrile illness.3 Exposure, outcome and covariate data were obtained from patient-level outpatient electronic health records linked to pharmacy and medical claims.3  
The analysis found that QIVc showed a clinical benefit compared to QIVe in prevention of test-confirmed influenza in the outpatient care setting, with estimated relative vaccine effectiveness (rVEs) (95% CI) of 14.8% (7.0 – 22.0) in 2017–-18, 12.5% (4.7 – 19.6) in 2018-–19 and 10.0% (2.7 – 16.7) in 2019–-20.3 Results of sensitivity analyses supported the robustness of the main analyses.3 The analysis highlighted the clinical value of QIVc compared with QIVe in preventing outpatient test-confirmed influenza over three seasons characterized by different circulating strains and degrees of egg adaptation.3 Estimated rVEs were consistent with previously published studies using influenza-like illness and lab-confirmed outcome.3

Study Limitations
The above studies featuring RWE were subject to the typical limitations associated with retrospective cohort analyses. Observational studies have limitations including the potential for selection bias and residual confounding. Individual study may include limitations such as retrospective analyses.

About Seasonal Influenza
Influenza is a frequently occurring, contagious seasonal respiratory disease that may cause severe illness and life-threatening complications in some people.4 Influenza can lead to clinical symptoms varying from mild to moderate respiratory illness to severe complications, hospitalization and in some cases, death.4 Because transmission of influenza viruses to others may occur before symptoms develop and up to 5 to 7 days after becoming sick, the disease can be easily transmitted to others.4 Preliminary estimates from the Centers for Disease Control and Prevention (CDC) report that during the 2022/23 influenza season, there were an estimated 300,000-650,000 influenza-related hospitalizations in the U.S.5 The CDC recommends annual vaccination for individuals aged 6 months and older, who do not have any contraindications.6 Since it takes about two weeks after vaccination for antibodies to develop in the body that help protect against influenza virus infection, it is recommended that people get vaccinated before influenza begins spreading in their community.6 The CDC recommends that people get vaccinated by the end of October.6

About CSL Seqirus
CSL Seqirus is part of CSL (ASX:CSL). As one of the largest influenza vaccine providers in the world, CSL Seqirus is a major contributor to the prevention of influenza globally and a transcontinental partner in pandemic preparedness. With state-of-the-art production facilities in the U.S., the U.K. and Australia, and leading R&D capabilities, CSL Seqirus utilizes egg, cell and adjuvant technologies to offer a broad portfolio of differentiated influenza vaccines in more than 20 countries around the world.

For more information about CSL Seqirus, visit

About CSL
CSL (ASX:CSL) (USOTC:CSLLY) is a global biotechnology company with a dynamic portfolio of lifesaving medicines, including those that treat haemophilia and immune deficiencies, vaccines to prevent influenza, and therapies in iron deficiency and nephrology. Since our start in 1916, we have been driven by our promise to save lives using the latest technologies. Today, CSL – including our three businesses: CSL Behring, CSL Seqirus and CSL Vifor – provides lifesaving products to patients in more than 100 countries and employs 32,000 people. Our unique combination of commercial strength, R&D focus and operational excellence enables us to identify, develop and deliver innovations so our patients can live life to the fullest. For inspiring stories about the promise of biotechnology, visit and follow us on
For more information about CSL, visit

Intended Audience 
This press release is issued from CSL Seqirus in Summit, New Jersey, USA and is intended to provide information about our global business. Please be aware that information relating to the approval status and labels of approved CSL Seqirus products may vary from country to country. Please consult your local regulatory authority on the approval status of CSL Seqirus products.
Forward-Looking Statements 
This press release may contain forward-looking statements, including statements regarding future results, performance or achievements. These statements involve known and unknown risks, uncertainties and other factors which may cause our actual results, performance or achievements to be materially different from any future results, performances or achievements expressed or implied by the forward-looking statements. These statements reflect our current views with respect to future events and are based on assumptions and subject to risks and uncertainties. Given these uncertainties, you should not place undue reliance on these forward-looking statements. 

Em Dekonor
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What is FLUCELVAX® QUADRIVALENT (Influenza Vaccine)? 

FLUCELVAX QUADRIVALENT is a vaccine that helps protect people aged 6 months and older from the flu. Vaccination with FLUCELVAX QUADRIVALENT may not protect all people who receive the vaccine. 

You should not get FLUCELVAX QUADRIVALENT if you have had a severe allergic reaction to any of the ingredients in the vaccine. 

Before receiving FLUCELVAX QUADRIVALENT, tell your healthcare provider about all medical conditions, including if you: 

  • Have ever had Gullain-Barré syndrome (severe muscle weakness) within six weeks of getting a flu vaccine. The decision to give FLUCELVAX QUADRIVALENT should be made by your healthcare provider, based on careful consideration of the potential benefits and risks. 
  • Have problems with your immune system or are taking certain medications that suppress your immune system, as these may reduce your immune response to the vaccine.
  • Have ever fainted when receiving a vaccine.

What are the most common side effects of FLUCELVAX QUADRIVALENT? 

  • Pain, redness, swelling, and/or a raised hardened area where the vaccine was given
  • Headache
  • Overtiredness with low energy
  • Muscle aches
  • Feeling unwell (malaise)

Additional side effects seen in children include: 

  • Tenderness or bruising where vaccine was given
  • Sleepiness
  • Irritability
  • Diarrhea
  • Changes in eating habits

These are not all of the possible side effects of FLUCELVAX QUADRIVALENT. You can ask your healthcare provider for more information and for advice about any side effects that concern you.  

To report SUSPECTED ADVERSE REACTIONS, contact CSL Seqirus at 1-855-358-8966 or VAERS at 1-800-822-7967 or 
You are also encouraged to report negative side effects of prescriptions drugs to the FDA. Visit or call 1-800-FDA-1088.

Before receiving this vaccine, please see the full US Prescribing Information for FLUCELVAX QUADRIVALENT. The information provided here does not include all that is known about FLUCELVAX QUADRIVALENT. To learn more, talk with your healthcare provider or pharmacist. 

FLUCELVAX® QUADRIVALENT is a registered trademark of CSL Seqirus UK Limited or its affiliates.  


McGovern I et al. Healthcare Resource Use and Complications Among Adults with an Influenza-Related Medical Encounter: 2015-2020 Influenza Seasons in the United States. Presented at ESWI 2023. 

Imran M et al. Relative Effectiveness of the MF59-Adjuvanted Influenza Vaccine vs High-Dose Influenza Vaccine in Older Adults with Influenza Risk Factors during the 2019-2020 U.S. Influenza Season. Presented at ESWI 2023. 

Stein AN et al. Superior Effectiveness of Cell-Based Versus Egg-Based Quadrivalent Influenza Vaccines Against Outpatient Test-Confirmed Influenza Over Three Consecutive Seasons in the United States. Presented at ESWI 2023. 

Centers for Disease Control and Prevention (CDC). (2022). Key Facts about Influenza. Retrieved from Accessed August 2023. 

CDC. (2023). 2022-2023 Preliminary In-Season Burden Estimate. Retrieved from: Accessed August 2023.

CDC. (2023). Who Needs a Flu Vaccine and When. Retrieved from: Accessed August 2023.