Recently Published Real-World Evidence Study Shows Effectiveness of Cell-Based Quadrivalent Influenza Vaccine Over Three Seasons

    --  A real-world evidence (RWE) study recently published in Open Forum
        Infectious Diseases (OFID) examined three consecutive U.S. flu seasons
        in the United States. The study suggests that cell-based quadrivalent
        influenza vaccine (QIVc) may have the potential to be more effective
        than egg-based vaccines (QIVe) in preventing test-confirmed
    --  The study results reveal that the relative vaccine effectiveness of QIVc
        versus QIVe in prevention of test-confirmed influenza was at least 10%
        higher across three consecutive flu seasons, 2017-2020.(1)

SUMMIT, N.J., May 2, 2024 /PRNewswire/ -- CSL Seqirus, a business of CSL (ASX: CSL), today announced a real-world evidence (RWE) study recently published in Open Forum Infectious Diseases (OFID), showing that a cell-based quadrivalent influenza vaccine (QIVc) prevented more test-confirmed influenza cases among individuals 4-64 years of age compared with the egg-based quadrivalent influenza vaccine (QIVe) over three consecutive U.S. influenza seasons (2017-2020).(1) These data add to the growing wealth of evidence supporting the benefits of cell-based influenza vaccines.

The study collected RWE from 31,824, 33,388, and 34,398 subjects in the 2017-2018, 2018-2019, and 2019-2020 seasons, respectively.(1) Findings show a higher relative effectiveness of QIVc over QIVe in the prevention of test-confirmed influenza, with estimated relative vaccine effectiveness (rVE) of 14.8% for the 2017-18 season, 12.5% for 2018-19, and 10.0% for 2019-20.(1) rVE means the effectiveness of one vaccine relative to another.

"This study exemplifies the value of RWE in generating valuable insights into the effectiveness of influenza vaccines," said Alicia N. Stein, Director, Real World Evidence, Center for Outcomes Research and Epidemiology, CSL Seqirus. "With data collected over three consecutive seasons, our study suggests higher vaccine effectiveness of cell-based quadrivalent influenza vaccines compared with standard egg-based influenza vaccines."

Influenza vaccines produced using egg-based manufacturing can undergo adaptation within the manufacturing process, which may result in a mismatch between the strains covered in the vaccine and those that are identified by the World Health Organization (WHO).(2)

"Cell-based technology allows us to provide an exact antigenic match to the WHO's identified strains, helping to improve vaccine effectiveness versus standard egg-based vaccines. These data build on the growing evidence of real-world data that shows the benefits of our cell-based influenza vaccine," said Gregg Sylvester, Chief Health Officer and Head of Medical Affairs, CSL Seqirus. "At CSL Seqirus, we're continually driving vaccine technology forward, in order to improve effectiveness and help keep communities healthy."

About the Study
Researchers used a retrospective test-negative design (TnD) to estimate the relative vaccine effectiveness (rVE) of QIVc versus QIVe among individuals aged 4-64 years who had an acute respiratory or febrile illness and were tested for influenza in routine outpatient care.(1) The study, the largest TnD RWE for QIVc to date, included 31,824, 33,388, and 34,398 subjects in the 2017-2018, 2018-2019, and 2019-2020 seasons, respectively; ~10% received QIVc and ~90% received QIVe.(1)

The results reveal higher relative vaccine effectiveness of QIVc versus QIVe in prevention of test-confirmed influenza; rVEs were 14.8% in 2017-2018, 12.5% in 2018-2019, and 10.0% in 2019-2020.(1)

Study Limitations
The above study featuring RWE was subject to the typical limitations associated with retrospective cohort analyses. Observational studies have limitations including the potential for selection bias and residual confounding. TnD studies offer significant advantages over other observational studies and reflect the real world, however they are not as definitive as Randomized Controlled Trials (RCTs) in establishing causality. We recommend interpreting these results within a comprehensive evidence framework that includes various study designs for a well-rounded perspective on vaccine efficacy/effectiveness.

About Seasonal Influenza
Influenza is a frequently occurring, contagious seasonal respiratory disease that may cause severe illness and life-threatening complications in some people.(3) Influenza can lead to clinical symptoms varying from mild to moderate respiratory illness to severe complications, hospitalization and in some cases, death.(3 )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.(3 )Preliminary estimates from the Centers for Disease Control and Prevention (CDC) report that during the 2023/24 influenza season, there have been an estimated 380,000-780,000 influenza-related hospitalizations in the U.S.(4) The CDC recommends annual vaccination for individuals aged 6 months and older, who do not have any contraindications.(5) 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.(5) The CDC recommends that most people get vaccinated by the end of October.(5 )

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 medicines, including those that treat hemophilia 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 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.


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 Guillain-Barré syndrome (severe muscle weakness) within
        six weeks after 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 prescription 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 Seqirus UK Limited or its affiliates.

Tiffany Cody
+1 (908) 370-1863


(1) Stein, Alicia N et al. "Relative vaccine effectiveness of cell-based versus egg-based quadrivalent influenza vaccine against test-confirmed influenza over three seasons between 2017 and 2020." Open Forum Infectious Diseases 2024. DOI:

(2) Peck, Heidi et al. "Enhanced isolation of influenza viruses in qualified cells improves the probability of well-matched vaccines." NPJ vaccines vol. 6,1 149. 9 Dec. 2021, DOI: 10.1038/s41541-021-00415-3.

(3) Centers for Disease Control and Prevention (CDC). (2024). Key Facts about Influenza. Retrieved from Accessed May 2024.

(4) CDC. (2024). 2023-2024 U.S. Flu Season: Preliminary In-Season Burden Estimates. Retrieved from: Accessed May 2024.

(5) CDC. (2024). Who Needs a Flu Vaccine and When. Retrieved from: Accessed May 2024.

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