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


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 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 influenza.
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 

Montreal QC | 2 May 2024

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 2017–2018 season, 12.5% for 2018–2019, and 10.0% for 2019– 2020.1 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 quadrivalent influenza vaccines.” 

“At CSL Seqirus, we are committed to reducing the burden caused by influenza, and our innovative technologies, such as cell-based manufacturing, help advance this mission through potential enhanced effectiveness and improved public health,” said Stefan Merlo, Vice President, Commercial Development, CSL Seqirus.

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.2  Influenza can lead to clinical symptoms varying from mild to moderate respiratory illness to severe complications, hospitalization and in some cases, death.2 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.2 Influenza causes an average of 12,200 hospitalizations and approximately 3,500 deaths each year in Canada.3  The National Advisory Committee on Immunization (NACI) recommends  that influenza vaccine should be offered annually to anyone 6 months of age and older who does not have a contraindication to the vaccine.3 Since it takes about two weeks after vaccination for antibodies to develop in the body and help protect against influenza virus infection, it is recommended that people get vaccinated before influenza begins spreading in their community.4 The NACI recommends that people get vaccinated as soon as feasible after the vaccines become available in the fall.3 

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

CSL Seqirus, FLUCELVAX® QUAD are trademarks of CSL Seqirus.

Intended Audience
This press release is issued from CSL Seqirus in Montreal, Quebec, Canada 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. 

Influenza Vaccine (surface antigen, inactivated, prepared in cell cultures)
Indication and clinical use:5

FLUCELVAX® QUAD is a quadrivalent inactivated vaccine indicated for active immunization of adults and children aged 6 months or older for the prevention of influenza disease caused by influenza virus subtypes A and types B contained in the vaccine.

Relevant warnings and precautions:5

As with all injectable vaccines, appropriate medical treatment and supervision should always be readily available in case of a rare anaphylactic event 
Postpone in patients with febrile illness
Clinically significant bleeding disorders
Endogenous or iatrogenic immunosuppression
Guillain-Barré syndrome
Syncope, presyncope 
Pregnant and nursing women
A protective immune response may not be elicited in all vaccine recipients

For more information: 
Please consult the Product Monograph at for important information relating to adverse reactions, drug interactions, and dosing information which have not been discussed in this piece. The Product Monograph is also available by calling us at 1-855-358-8966.

Media Contact
Tiffany Cody
+1 (908) 370-1863


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  Centers for Disease Control and Prevention (CDC). (2022). Key Facts about Influenza. Retrieved from Accessed April 2024. 

3  Advisory Committee on Immunization (NACI). Statement on Seasonal Influenza Vaccine for 2024–2025. Accessed April 2024. 

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

5 FLUCELVAX® QUAD Product Monograph.