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New Data at OPTIONS XI Conference Highlight Burden of Seasonal Influenza on Health Systems and the Need for Increased Vaccination Rates


CSL Seqirus, a business of CSL Limited (ASX:CSL), today announced new data highlighting the significant burden influenza places on hospitals and healthcare resource use, as well as on more vulnerable populations such as children. The data are being presented in oral and poster sessions at OPTIONS for the Control of Influenza XI (OPTIONS XI), being held in Belfast, United Kingdom, from September 26-29, 2022.  

The World Health Organization (WHO) estimates that seasonal influenza results in up to 650,000 respiratory deaths each year.1 In the U.S. specifically, influenza caused up to 52,000 deaths and 710,000 hospitalizations annually between 2010-2020, according to the U.S. Centers for Disease Control and Prevention (CDC).2 Both organizations recommend annual influenza vaccination as the most effective way to prevent influenza, particularly given the continued co-circulation with COVID-19.3,4 

A new study presented at OPTIONS XI suggested that when COVID-19 and influenza viruses are co-circulating, the U.S. influenza immunization rate should be raised from 45 percent to 70 percent, or higher, to avoid saturation of hospital system resources, such as those associated with intensive care unit (ICU) beds.5 Another study evaluated how influenza risk factors across five influenza seasonal cohorts, with sizes ranging from 887,260 to 3,628,168 individuals, can predict a person’s potential for severe outcomes, and found a correlation between an individual’s number of risk factors and hospitalization.6  

“The COVID-19 pandemic and recently active flu season in the Southern Hemisphere attest to the burden high rates of respiratory infections, including influenza, can place on hospitals, which are the vanguard of a nation’s health system,” said Dr. Gregg Sylvester, Chief Health Officer, CSL Seqirus.7 “Data presented at OPTIONS XI help us better understand the impact of vaccination on healthcare resources we all depend on such as ER and ICU bed capacity. This will become even more important in a world where COVID-19 and influenza are likely to continue co-circulating.”

A retrospective database analysis of 10 consecutive influenza seasons in Italy found that seasonal influenza placed a significant burden on the pediatric population as measured by pediatrician visits, emergency room visits and hospital admissions, with an average of 8,892 influenza cases among approximately 150,000 children under the age of 14 years each season.8 

“The study conducted in Italy offers new insights into the incidence and impact of influenza in a pediatric population in the EU, where influenza vaccination is not recommended across all Member States,” said Mendel Haag, Senior Director, Center of Outcomes Research & Epidemiology, CSL Seqirus.8 “One of the benefits of real-world databases is the ability to connect and analyze data sources over multiple influenza seasons, allowing us in this case to demonstrate the burden children experience. This study found that in the Veneto Region alone, there were more than 12,000 reported influenza cases associated with 220 ER visits and 111 hospitalizations over a 3-season period.”8

As a global leader in influenza protection, CSL Seqirus recognizes its responsibility to help reduce the burden of influenza on health systems and communities, including vulnerable populations like children, around the world.


The U.S. Influenza Immunization Rate Reduction and Its Impact on Hospital System Resources. An Influenza and COVID-19 Co-Circulation Scenario. (Poster presentation: Monday, September 26, 2022, #P-193)

During the 2021/22 influenza season in the U.S., the overall vaccination rate dropped to 45 percent, a rate below pre-pandemic levels. To estimate the impact of this reduced rate on hospital resources when influenza and COVID-19 viruses are co-circulating, researchers employed a predictive modeling study that assumed vaccination with standard-dose, egg-based, quadrivalent flu vaccines for all ages, a total number of 1,000,000 acute hospital and 100,000 ICU hospital beds in the U.S., and a regular occupancy rate of 70 percent related to other diseases. The model used the current U.S. influenza vaccination rate of 45 percent and an average vaccine effectiveness rate of 42 percent based on estimates from CDC reports for the last 10 seasons. The COVID-19 variants were used to create an average scenario on the impact on acute beds and ICU beds occupied due to COVID-19.5 

The model estimated that the number of acute hospital and ICU hospital beds used for influenza would be 183,778 and 27,891, respectively, over a high influenza incidence season and 57,521 and 8,850 for a low influenza incidence season. During a COVID-19 pandemic setting, this would generate significant pressure on the U.S. hospital system, especially in a high influenza incidence season, and would saturate the number of ICU hospital beds, which are assumed to be at 1,000,000 and 100,000, respectively. The researchers concluded that regardless of the severity of the flu season, preventing any saturation of acute hospital or ICU hospital beds would occur only if the vaccination rate for influenza vaccines was increased to 70 percent or higher.5  

A Retrospective Database Analysis to Estimate the Epidemiology and Burden of Influenza in Children 0-14 Years Over 10 Consecutive Seasons. (Poster presentation: Monday, September 26, 2022, #P-185)

To determine the incidence and impact of influenza on the pediatric population in Italy and the associated healthcare utilization, researchers analyzed data from Pedianet, a pediatric primary-care database, over a 10-year period (2010-2011 through 2019-2020).8 

The analysis found an average of 8,892 influenza cases among approximately 150,000 children ages zero to 14 each season. The incidence of influenza, as assessed by pediatrician visit, emergency room visit or hospital admission, was highest among children ages one to four, and lowest among children younger than six months. In the region of Italy for which hospitalization data was available, 12,416 influenza cases were reported from January 2017 to March 2020. These cases were associated with 220 emergency room visits and 111 hospitalizations. The researchers concluded that influenza had a significant burden on children ages 14 years and under in Italy during the 10-year period.8

Effects of Stacking Influenza Risk Factors on Odds of Influenza-Related Hospitalization. (Oral presentation: Wednesday, September 28, 2022, #AOXI0245)

To evaluate how risk factors (as defined by the CDC) for influenza affect the likelihood of being hospitalized for influenza, researchers used statistical models to conduct a retrospective analysis of electronic medical records and associated medical claims for people ages 18 and older across five seasonal cohorts (2015/16 through 2019/20 seasons).6 

The analysis showed that a majority of patients 50 years of age or older had at least one risk factor. Across age groups, each increase in the number of risk factors (from 0 to 4+) an individual had consistently resulted in an increase in the odds of influenza-related hospitalization in each of the five-seasonal cohorts. For the overall population, people with one risk factor had 1.8 times the odds and people with four risk factors had 6.4 times the odds of being hospitalized for influenza compared to people with no risk factors. The researchers concluded that the number of influenza risk factors can be highly informative of a person’s potential for severe influenza outcomes.6 

Study Limitations
The above studies 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 limitations may include: retrospective analyses, a potential lack of laboratory confirmed influenza, and varying data sources.

About Seasonal Influenza
Influenza is a common, contagious seasonal respiratory disease that may cause severe illness and life-threatening complications in some people.9 Influenza can lead to clinical symptoms varying from mild to moderate respiratory illness to severe complications, hospitalization and in some cases, death.9 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.9 Estimates from the Centers for Disease Control and Prevention (CDC) report that during the 2019/20 influenza season, there were an estimated 405,000 influenza-related hospitalizations in the U.S.10 The CDC recommends annual vaccination for individuals aged 6 months and older, who do not have any contraindications.4 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.4 The CDC recommends that people get vaccinated by the end of October.4 

About CSL Seqirus
CSL Seqirus is a business of CSL Limited (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. 

About CSL
CSL (ASX: CSL; USOTC: CSLLY) is a leading global biotechnology company with a dynamic portfolio of lifesaving medicines, including those that treat haemophilia 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 three businesses, CSL Behring, CSL Seqirus and CSL Vifor – provides lifesaving products to patients in more than 100 countries and employs 30,000 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. 



Jon Steed
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The World Health Organization (WHO). Global Influenza Programme. Retrieved from: Accessed September 2022. Accessed September 2022.

Centers for Disease Control and Prevention (CDC). (2022). Burden of Flu. Retrieved from: Accessed September 2022. 

WHO. (2018). Influenza (Seasonal). Retrieved from: Accessed September 2022.

Centers for Disease Control and Prevention (CDC). (2021). Who Needs a Flu Vaccine and When. Retrieved from: Accessed September 2022. 

Nguyen, V.H. & Mould-Quevedo, J.F. (2022). The U.S. Influenza Immunization Rate Reduction and its Impact on Hospital System Resources. An Influenza and COVID-19 Co-Circulation Scenario. Presented at OPTIONS XI, September 2022.

McGovern, I., Bogdanov, A., Cappell, K., & Haag, M. (2022). Effects of Stacking Influenza Risk Factors on Odds of Influenza-Related Hospitalizations. Presented at OPTIONS XI, September 2022.

Australian Government Department of Health. Australian Influenza Surveillance Report. Retrieved from: Accessed September 2022.

Barbieri, E., Porcu, G., Dona, D., et al. (2022). A Retrospective Database Analysis to Estimate the Epidemiology and Burden of Influenza in Children 0-14 Years Over 10 Consecutive Seasons. Presented at OPTIONS XI, September 2022.

Centers for Disease Control and Prevention (CDC). (2021). Key Facts about Influenza. Retrieved from Accessed September 2022.

10 Centers for Disease Control and Prevention (CDC). (2021). Estimated Influenza Illnesses, Medical visits, Hospitalizations, and Deaths in the United States – 2019-2020 Influenza Season. Retrieved from: Accessed September 2022.