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Seqirus Publishes New Real-World Evidence Supporting the Effectiveness of Adjuvanted Seasonal Influenza Vaccine in Adults 65 Years and Older in Clinical Infectious Diseases

Company announces the publication of new real-world evidence on effectiveness of the MF59® adjuvanted, trivalent influenza vaccine (aTIV).


Summit, NJ, - Seqirus, a global leader in influenza prevention, today announced the publication of new real-world evidence (RWE) on the company's MF59® adjuvanted, trivalent influenza vaccine (aTIV) in the peer-reviewed medical journal Clinical Infectious Diseases.1 Study results indicate aTIV was more effective in reducing influenza-related medical encounters compared with standard egg-based quadrivalent influenza vaccine (QIVe) and high-dose trivalent influenza vaccine (TIV-HD) among adults 65 years and older during the 2017/18 and 2018/19 U.S. influenza seasons.1 

“The use of large, real-world datasets allows for the evaluation of effectiveness on a scale not typically analyzed in a randomized trial,” said Constantina Boikos, lead study author and Senior Manager, Center for Outcomes Research & Evaluation at Seqirus. “This retrospective cohort study, which includes 10.6 million vaccinated U.S. individuals, demonstrates the value that RWE can provide by illustrating the effectiveness of influenza vaccines in real-world settings.”1  

In the U.S., influenza causes significant morbidity and mortality in adults 65 years and older, as demonstrated by higher hospitalization and death rates in more recent years, compared with young, healthy adults.2 Seasonal influenza vaccine efficacy may be impacted by age-related immune decline in this population, which can result in reduced immune response to influenza vaccines.3,4 The MF59® adjuvant included in aTIV is designed to enhance the immune response to the antigens contained in the vaccine in adults 65 years and older. 5,6,7  

“While influenza activity has been generally low during the 2020/21 season due to social distancing, mask wearing, flu vaccination and other measures in place to mitigate the spread of COVID-19, the CDC has said that influenza is a risk even during the COVID-19 pandemic, especially as individuals begin to increase their social interactions again,” said Gregg Sylvester, MD, Chief Medical Officer at Seqirus.8 “The role of influenza vaccines remains critically important as an effort to reduce the risk of seasonal influenza, especially for adults 65 years and older who are at a higher risk for complications.” 

The MF59® adjuvant is designed to strengthen, broaden and increase the duration of the immune response.9,10 This may be important when there is a mismatch between the virus strains included in the vaccine and the strains circulating in the community.7,11 The quadrivalent formulation of the MF59® adjuvanted influenza vaccine (aQIV), which adds an additional B strain to the trivalent formulation, was approved by the U.S. Food and Drug Administration (FDA) in February 2020 and in Europe in June 2020.12 

Both aTIV and aQIV, which include the MF59® adjuvant have an extensive clinical legacy, with 181+ million doses distributed over 20+ years* and licensure in 30 countries.13

*Doses distributed globally as of February 2021, including both trivalent and quadrivalent formulations.

About the Study 
This Seqirus-sponsored and conducted retrospective cohort analysis compared relative vaccine effectiveness (rVE) of an MF59® adjuvanted egg-based, trivalent influenza vaccine (aTIV), egg-based quadrivalent influenza vaccines (QIVe), and high-dose trivalent influenza vaccine (TIV-HD), in preventing influenza-related medical encounters in U.S. subjects 65 years and older during the 2017/18 and 2018/19 influenza seasons.1  

The final cohort for the 2017/18 season comprised 4.8 million subjects, of which 524,223 (10.9%) received aTIV; 917,609 (19.0%) received QIVe; and 3,377,860 (70.1%) received TIV-HD.1 The 2018/19 cohort comprised 5.8 million patients, of which 1,031,145 (17.9%) received aTIV, 1,031,145 (17.9%); 915,380 (15.9%) received QIVe; and 3,809,601 (66.2%) received TIV-HD.1 

An integrated dataset was created by linking patient-level electric medical records (EMRs) with pharmacy and medical claims data, where available.1 Individuals were included in the analysis if they had a record of vaccination from August 1, 2017-February 28, 2018 (first season) and August 1, 2018-February 28, 2019 (second season).1 The primary outcome was influenza-related medical encounters which included both inpatient and outpatient settings.1 Adjusted odds rations (ORs) were estimated using a logistic regression model in the overall study cohort and in sub-cohorts (65-75, 75-84 and ≥85 years of age) defined by age.1 The rVE was calculated as 100*(1 – ORadjusted) and reported with 95% confidence intervals (CI).1

In 2017/18, when adjusted for demographic confounders, rVE for aTIV vs. QIVe was 18.2 (95% confidence interval [CI]: 15.8, 20.5) and aTIV vs. TIV-HD was 7.7 (95% CI: 2.3, 12.8).1 In the 2018/19 season, the adjusted rVE value for aTIV vs. QIVe was 27.8 (95% CI: 25.7, 29.9) and for aTIV vs. TIV-HD was 6.9 (95% CI: 3.1, 10.6).1 Results remained similar for age-related subgroup analyses during both seasons.

The results of this study indicate that aTIV was more effective in reducing influenza-related medical encounters versus QIVe and TIV-HD, among approximately 11 million vaccinated U.S. individuals 65 years and older during the 2017/18 and 2018/19 seasons.1

Although this study uses a large, real-world dataset integrating different sources of patient information, a limitation of this study was that the effectiveness outcome was based on diagnostic codes rather than laboratory-confirmed influenza.1 Consistent results were observed, however, when the observation window was limited to consecutive weeks with the highest laboratory-confirmed influenza activity identified using CDC data.1 Another limitation is the evaluation of subjects with both EMR and claims data available, thus limiting the study population to insured individuals.1 

A similar analysis of the relative effectiveness of aTIV in individuals at high-risk of influenza and its complications was presented at IDWeek 2020.14

About Seasonal Influenza 
Influenza is a common, contagious seasonal respiratory disease that may cause severe illness and life-threatening complications in some people.15  Influenza can lead to clinical symptoms varying from mild to moderate respiratory illness to severe complications, hospitalization and in some cases, death.15 The CDC recommends annual vaccination for individuals aged 6 months and older, who do not have any contraindications.16  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.15 Preliminary estimates from the CDC report that from October 1, 2019, through April 4, 2020, there were an estimated 410,000 to 740,000 influenza-related hospitalizations in the U.S.17 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.18 The CDC recommends that people get vaccinated by the end of October.18 Getting vaccinated too early (for example, in July or August), can be associated with reduced protection against influenza infection later in the flu season.18 However, getting vaccinated later can still be beneficial and vaccination should continue to be offered throughout the influenza season, even into January or later.18

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 70 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

For more information visit and

Intended Audience

This press release is issued from Seqirus U.S. Inc. in Summit New Jersey, U.S. 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.

FLUAD® (Influenza Vaccine, Adjuvanted) and FLUAD® QUADRIVALENT (Influenza Vaccine, Adjuvanted)

What is FLUAD® (Influenza Vaccine, Adjuvanted) and FLUAD® QUADRIVALENT (Influenza Vaccine, Adjuvanted)?
FLUAD and FLUAD QUADRIVALENT are vaccines that help protect people aged 65 years and older from the flu. Vaccination with FLUAD or FLUAD QUADRIVALENT may not protect all people who receive the vaccine.

Who should not get FLUAD or FLUAD QUADRIVALENT? 
You should not get FLUAD or FLUAD QUADRIVALENT if you have had a severe allergic reaction to any of the ingredients in the vaccine in the past, including egg protein, or a severe allergic reaction to a previous influenza vaccine. 

Before receiving FLUAD or FLUAD 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 FLUAD or FLUAD 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 FLUAD and FLUAD QUADRIVALENT? 

  • Pain or tenderness where the vaccine was given 
  • Muscle aches 
  • Headache
  • Fatigue

These are not all of the possible side effects of FLUAD or FLUAD QUADRIVALENT. You can ask your healthcare provider for more information. 

What do I do if I have side effects? 
Ask your healthcare provider for advice about any side effects that concern you. 

To report SUSPECTED ADVERSE REACTIONS, contact Seqirus USA Inc. at 1‐844‐275‐ 2461 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 FLUAD or FLUAD QUADRIVALENT. 
The information provided here does not include all that is known about FLUAD or FLUAD QUADRIVALENT. To learn more, talk about FLUAD with your healthcare provider. 
FLUAD®, FLUAD® QUADRIVALENT, and MF59® are registered trademarks of Seqirus UK Limited or its affiliates.


Polina Miklush  
+1 (908) 608-7170


1Boikos, C., Fischer, L., O’Brien, D., et al. (2020). Relative Effectiveness of Adjuvanted Trivalent Inactivated Influenza Vaccine Versus Egg-Derived Quadrivalent Inactivated Influenza Vaccines and High-Dose Trivalent Influenza Vaccine in Preventing Influenza-Related Medical Encounters in US Adults ≥65 Years During the 2017-2018 and 2018-2019 Influenza Seasons. Clinical Infectious Diseases, 2021;, ciab152, 

2Centers for Disease Control and Prevention (CDC). (2019). People 65 years and Older & Influenza. Retrieved from: Accessed March 2021. 

3Monto AS, Ansaldi F, Aspinall R, et al. (2009). Influenza control in the 21st century: Optimizing protection of older adults. Vaccine. 2009;27(37):5043-5053.

4McElhaney JE, Verschoor CP, Andrew MK, et al. (2020). The immune response to influenza in older humans: beyond immune senescence. BMC.

5Frey SE, Aplasca-De Los Reyes MR, Reynales H, et al. (2014). Comparison of the safety and immunogenicity of an MF59®-adjuvanted with a non-adjuvanted seasonal influenza vaccine in elderly subjects. Vaccine. 2014;32:5027-5034.

6O'Hagan DT, Ott GS, Nest GV, et al. (2013). The history of MF59® adjuvant: a phoenix that arose from the ashes. Expert Rev Vaccines. 2013;12(1):13-30.

7Banzhoff A, Pellegrini M, Del Giudice G, et al. (2008). MF59-adjuvanted vaccines for seasonal and pandemic influenza prophylaxis. Influenza Other Respir Viruses. 2008;2(6):243-24.

8CDC. (2019). Frequently Asked Influenza (Flu) Questions: 2020-2021 Season. Retrieved from: Accessed March 2021.

9Camilloni B, Neri M, Lepri E, Iorio AM. Cross-reactive antibodies in middle-aged and elderly volunteers after MF59-adjuvanted subunit trivalent influenza vaccine against B viruses of the B/Victoria or B/Yamagata lineages. Vaccine. Jun 2009;27(31):4099-103. doi:10.1016/j.vaccine.2009.04.078.

10Kavian N, Hachim A, Li AP, et al. Assessment of enhanced influenza vaccination finds that FluAd conveys an advantage in mice and older adults. Clin Transl Immunology. 2020;9(2):e1107. doi:10.1002/cti2.1107.

11Ansaldi F, Zancolli M, Durando P, et al. Antibody response against heterogeneous circulating influenza virus strains elicited by MF59- and non-adjuvanted vaccines during seasons with good or partial matching between vaccine strain and clinical isolates. Vaccine. 2010;28(25):4123-4129.

12FLUAD® QUADRIVALENT (Influenza Vaccine, Adjuvanted) [package insert]. Holly Springs, NC: Seqirus Inc; 2020.

13Data on file. Seqirus Inc; 2021.

14Boikos, C. Fischer, L. O’Brien, D. et al. Relative Effectiveness of aIIV3 versus IIV4 and HD-IIV3 In Preventing Influenza-Related Medical Encounters in Adults ≥65 Years of Age at High Risk for Influenza Complications During the U.S. 2017-2018 and 2018-2019 Influenza Seasons. Presented at ID Week 2020.

15CDC. (2019). Key Facts about Influenza (Flu). Retrieved from:  Accessed March 2021.

16CDC. (2020). Key Facts About Seasonal Flu Vaccine. Retrieved from: Accessed March 2021.

17CDC. (2020). 2019-2020 U.S. Flu season: Preliminary burden estimates. Retrieved from: Accessed March 2021.

18CDC. (2020). Who Needs a Flu Vaccine and When. Retrieved from: Accessed March 2021.