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Seqirus Presents New Phase 3 Clinical Data Supporting Use of Cell-Based Seasonal Influenza Vaccine in Children Six Months Through <4 Years of Age


Seqirus, a global leader in influenza prevention, presented new Phase 3 clinical data demonstrating that the company’s cell-based quadrivalent seasonal influenza vaccine (QIVc) was as safe and immunogenic as a standard quadrivalent seasonal influenza vaccine (QIV) in children six months through <4 years of age during the U.S. 2019/20 influenza season.These data were presented at the Pediatric Academic Society (PAS) virtual Annual Meeting on May 1, 2021.

“There is a significant disease burden of influenza for young children, and the CDC recognizes this population as one of high-risk for serious complications from the flu” said Brandon J. Essink, MD, CPI, medical director at Meridian Clinical Research and principal investigator of the study.2 “The results of this study provide evidence for the benefit of QIVc for pediatric patients, adding to a strong body of evidence in support of cell-based manufacturing for influenza vaccines.” 

The Centers for Disease Control and Prevention (CDC) recommends annual seasonal influenza vaccine as the best way to prevent influenza for everyone six months of age and above without contraindications.3 Children younger than five years of age, especially those under two years of age, are at high risk of developing serious influenza-related complications.2 Since 2010, estimated annual influenza-related hospitalizations among children younger than five years of age have ranged from 7,000-26,000 in the U.S.2

This Phase 3 clinical study was designed to support an application currently under review with the U.S. Food and Drug Administration (FDA) for an expanded age indication for people six months of age and above for QIVc, marketed as FLUCELVAX® QUADRIVALENT in the U.S.

“As COVID-19 mitigation tactics like social distancing relax, influenza vaccination remains of critical importance,” said Jonathan Edelman, MD, VP of Clinical Development at Seqirus and study author. “According to the CDC, this year there was a notable increase in influenza vaccination rates in the U.S. and as part of our mission to protect public health, we are working to ensure as many eligible people as possible have access to a differentiated influenza vaccine, including young children.”4

There are several factors that can impact seasonal influenza vaccine effectiveness, which may include vaccine recipient characteristics such as age and health, or a mismatch between circulating strains and the influenza strains contained within the seasonal influenza vaccine.5 Traditional egg-based vaccine production can cause the strain to mutate, which may lead to an antigenic mismatch between the circulating strains and the inactivated influenza strains contained within the seasonal influenza vaccine.5

QIVc utilizes a cell-based influenza vaccine manufacturing process, an alternative to traditional egg-based manufacturing.5 Cell-based influenza vaccines are designed to produce an exact match to those selected by the World Health Organization.5,6  Cell-based influenza vaccine technology may offer additional advantages over the standard influenza manufacturing process, including being more scalable and offering faster production in the event of an influenza pandemic.5 

These clinical data are an addition to a growing body of evidence supporting the safety and utility of cell-based influenza vaccines like QIVc.7 

In the U.S., Seqirus operates a state-of-the-art cell-based manufacturing facility in Holly Springs, North Carolina, purpose-built in partnership with the Biomedical Advanced Research and Development Authority (BARDA) to increase cell-based vaccine manufacturing capacity and combat pandemic influenza threats.8 Last year, Seqirus announced plans to build a new, world-class cell-based manufacturing facility in Australia, which will be the only cell-based influenza vaccine manufacturing facility in the Southern Hemisphere.9  

About the Study 
This Phase 3 observer-blind controlled study conducted in the U.S., evaluated whether a cell-based quadrivalent seasonal influenza vaccine (QIVc) would elicit a non-inferior immune response compared to a US-licensed quadrivalent influenza vaccine (QIV) in subjects six months through <4 years of age during the 2019/20 Northern Hemisphere influenza season.1 The study randomized 2414 children 2:1 to receive QIVc or QIV.1 Participants received one or two vaccine doses (28 days apart) based on vaccination history and were followed for at least 180 days.1

Non-inferiority of QIVc compared to QIV was concluded, if the upper bound of the two-sided 95% confidence interval (CI) for the postvaccination geometric mean titer (GMT) ratio does not exceed 1.5 and the seroconversion rate (SCR) difference does not exceed 10% for each of the 4 strains tested (A/H1N1, A/H3N2, B/Yamagata and B/Victoria).1

Safety profiles were also comparable between QIVc and QIV.1 The most common solicited AEs were similar between vaccinated groups (tenderness, erythema at the injection site, irritability, and sleepiness).1 The rate of serious AEs was <1% for each vaccine group.1

This study provides supportive data for a supplemental Biologics License Application (sBLA) filing for use of QIVc for immunization against seasonal influenza in the U.S. for persons six months and above. 

About Seasonal Influenza
Influenza is a common, contagious seasonal respiratory disease that may cause severe illness and life- threatening complications in some people.10 Influenza can lead to clinical symptoms varying from mild to moderate respiratory illness to severe complications, hospitalization and in some cases, death.10 The CDC recommends annual vaccination for individuals aged 6 months and older, who do not have any contraindications.3 Because transmission of influenza viruses to others may occur one day before symptoms develop and up to 5 to 7 days after becoming sick, the disease can be easily transmitted to others.10 Estimates from the CDC report that during the 2019/20 influenza season, there were an estimated 405,000 influenza-related hospitalizations in the U.S.11 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.12  The CDC recommends that people get vaccinated by the end of October.12 Getting vaccinated too early (for example, in July or August), can be associated with reduced protection against influenza infection later in the flu season.12 However, getting vaccinated later can still be beneficial and vaccination should continue to be offered throughout the influenza season, even into January or later.12

About Seqirus
Seqirus is part of CSL Limited (ASX: CSL). As one of the largest influenza vaccine providers in the world, 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, Seqirus utilizes egg, cell and adjuvant technologies to offer a broad portfolio of differentiated influenza vaccines in more than 20 countries around the world.

About CSL
CSL (ASX:CSL) is a leading global biotechnology company with a dynamic portfolio of life-saving medicines, including those that treat hemophilia and immune deficiencies, as well as vaccines to prevent influenza. Since our start in 1916, we have been driven by our promise to save lives using the latest technologies. Today, CSL — including our two businesses, CSL Behring and Seqirus - provides life- saving products to more than 100 countries and employs more than 27,000 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 more information about CSL Limited, visit

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Intended Audience
This press release is issued from Seqirus USA Inc. 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 Seqirus products may vary from country to country. Please consult your local regulatory authority on the approval status of 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 2 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, or a raised hardened area or swelling where the vaccine was given
  • headache
  • tiredness
  • muscle aches
  • feeling unwell (malaise)

Additional side effects seen in children include:

  • tenderness or bruising where vaccine was given
  • sleepiness
  • irritability
  • 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 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.

Polina Miklush
+1 (908) 608-7170


 1 Essink, B., Herringa, M., Jeanfreau, R., et al. (2021). Immunogenicity and Safety of Cell-derived Quadrivalent Influenza Vaccine in Children 6 through 47 Months of Age: A Randomized Controlled Non-Inferiority Trial. Presented at Pediatric Academic Societies 2021. 

 2Centers for Disease Control and Prevention (CDC). (2020). Flu & Young Children. Retrieved from: Accessed April 2021.

 3CDC. (2020). Key Facts About Seasonal Flu Vaccine. Retrieved from: Accessed April 2021.

 4CDC. (2020). Weekly National Flu Vaccination Dashboard. Retrieved from: Accessed April 2021.

 5CDC. (2020). Cell-Based Flu Vaccines. Retrieved from: Accessed April 2021.

 6Rajaram, S., Boikos, C., Gelone, et al. (2020). Influenza Vaccines: The Potential Benefits of Cell-Culture Isolation and Manufacturing.

 7Seqirus. (2021). New Seqirus Data Published in Vaccines Highlight Effectiveness and Economic Benefit of Cell-Based Quadrivalent Seasonal Influenza Vaccine (QIVc) in the 2018/19 U.S. Influenza Season. Retrieved from: 

  8This project has been funded in whole or in part with Federal funds from the Office of the Assistant Secretary for Preparedness and Response, Biomedical Advanced Research and Development Authority, under contract numbers HHSO10020060001F2C, HHSO100200700030C, HHSO100200900101C and HHSO100201200003I.

 9Data on file. (2020). Seqirus USA Inc.

 10CDC. (2019). Key Facts about Influenza (Flu). Retrieved from: Accessed April 2021.

 11CDC. (2020). Estimated Influenza Illnesses, Medical visits, Hospitalizations, and Deaths in the United States — 2019–2020 Influenza Season. Retrieved from: Accessed April 2021.

 12CDC. (2020). Who Needs a Flu Vaccine and When. Retrieved from: Accessed April 2021.