Flucelvax® Influenza Vaccine Clinical Trials, Efficacy, Indication, Side Effects
CSL Seqirus Flucelvax® is a cell culture-based influenza vaccine that protects people against various virus strains, as recommended by the World Health Organization (WHO). Flucelvax is the first and only trivalent cell-based influenza vaccine indicated for use in individuals six months and older who do not have the B/Yamagata influenza virus strain. Approved by the U.S. Food and Drug Administration (FDA) in 2012 and 2016, Flucelvax is indicated (STN: BL 125408, BL 125408/586) for everyone six months and older eligible to receive an influenza vaccine for active immunization for the prevention of influenza disease caused by influenza virus subtypes A and types B contained in the vaccine.
Flucelvax is the first FDA-approved flu vaccine to use cells instead of chicken eggs. It represents the first significant advance in flu vaccine manufacturing technology since flu vaccine production began in the 1930s. This modern manufacturing process enables the flu shot to be antibiotic-free, helps protect against the four identified flu strains for the 2020-2021 season, and is well-tolerated. Moreover, cell-based flu vaccine production does not use flu viruses grown in eggs and is not dependent on the availability of eggs. Additionally, cell-based flu vaccines that utilize cell-based candidate vaccine viruses (CVVs) can provide better protection than traditional, egg-based flu vaccines.
The U.S. Centers for Disease Control and Prevention (CDC) confirmed in 2023 that viruses used to make cell-based vaccines may be more similar to circulating "wild" flu viruses than those used to make egg-based vaccines. Cell-based influenza vaccine technology may offer advantages over the standard influenza manufacturing process, including greater scalability and faster production during an influenza pandemic. On June 21, 2023, the Advisory Committee on Immunization Practices (ACIP) presented considerations and proposed recommendations for the 2023-2024 flu season in the U.S. On February 22, 2023, the CDC's ACIP agenda highlighted preliminary data on the effectiveness of cell-based influenza vaccines (i.e., Flucelvax) during the 2022-23 flu season.
On July 10, 2025, CSL Seqirus announced that the Company had commenced shipping its differentiated portfolio of influenza vaccines for the 2025/26 U.S. season.
In the United Kingdom and European Union, Flucelvax is marketed as FLUCELVAX® TETRA.
CSL Seqirus reported on February 12, 2024, a half-year revenue of $ 1.804 billion, which was up 2% over the same period last year. In the U.S., CSL Seqirus operates a state-of-the-art cell-based manufacturing facility in Holly Springs, NC, 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. On August 15, 2023, the Company announced that significant progress had been made on constructing the new cell-culture influenza vaccine facility in Melbourne, which is expected to be operational by 2026. Seqirus is part of CSL Limited (ASX: CSL), headquartered in Melbourne, Australia. The CSL Group employs over 20,000 people in more than 60 countries.
Flucelvax Vaccine Effectiveness
Additionally, data presented by the Marshfield Clinic Research Institute on February 22, 2023, demonstrated that cell-based influenza vaccines, such as FluecelVax, provided 71% effectiveness in children between 6 months and 18 years old and 54% effectiveness among adults aged 18 years and older.
Flucelvax Vaccine Indication
A six-month or longer age indication for FLUCELVAX is approved in the U.S., Argentina, Canada, Taiwan, Australia & New Zealand to prevent disease caused by influenza A and type B viruses in the vaccine. For additional information on Seqirus influenza vaccines for the upcoming flu season, as well as resources about vaccination campaigns and CDC guidance, visit flu360.com.
Flucelvax Vaccine Pediatric
A study funded by Seqirus CLS and published on October 15, 2023, concluded that using a QIVc is effective in pediatric patients, with evidence of incremental benefits over using a QIVe in preventing hospitalizations and influenza-related medical encounters in nearly all published studies. The use of QIVc in pediatric populations is cost-effective when incorporated into a broader scheme that spans multiple age groups. The lack of potential for mismatch due to egg adaptation, combined with manufacturing benefits, means that cell-based influenza vaccines can play an essential role in population-level protection against Influenza.
Flucelvax Vaccine Pregnancy
On October 25, 2023, Gregg C. Sylvester, MD, MPH, Seqirus, presented at the ACIP Meeting - Pregnancy Outcomes with ccIIV4 (Flucelvax); Post Marketing Study. The independent expert committee found no evidence of a safety concern. These data support the use of ccIIV4 for immunization against Influenza in pregnant women and the fetus/infant population. Additionally, Nicky Klein, MD, PhD, Director of the Kaiser Permanente Vaccine Study Center, presented the safety of the quadrivalent recombinant influenza vaccine in pregnant women and their infants. In summary, within a large population of influenza-vaccinated pregnant women, no differences were observed in pregnancy, birth, and neonatal/infant outcomes when comparing RIV4 with SD-IIV4. No safety concerns were identified after RIV4 use in pregnancy.
CSL Seqirus presented original safety data at the Infectious Diseases Society for Obstetrics and Gynecology annual meeting from a new prospective observational cohort study evaluating pregnancy outcomes and fetal events of interest following vaccination with the Company's cell-based Flucelvax QIVc. The study found no unexpected adverse pregnancy outcomes in pregnant women in the U.S. who were vaccinated with QIVc.
On July 30, 2021, Seqirus announced a 'prospective observational cohort study that evaluated pregnancy outcomes and events of interest in the fetus or infant following vaccination with QIVc during any trimester. "Pregnant people (women) and people (women) who have recently given birth can be particularly vulnerable to infectious diseases like influenza," commented Christopher Robinson, M.D., MSCR, Charleston Maternal-Fetal Medicine and study author, in a press release. "These data provide further reassurance on the safe use of seasonal influenza vaccines in pregnant people (women)."
Flucelvax Vaccine Price
CSL Seqirus provides a coding and billing guide for healthcare providers.
Flucelvax Vs. Egg-Based Vaccines
On December 19, 2023, the Original Research should have presented real-world evidence (RWE) evaluating clinical outcomes among seniors aged 65 years or older, indicating a superior clinical benefit of all adjuvanted trivalent vaccines over standard egg-derived quadrivalent inactivated influenza vaccines. In a meta-analysis of RWE from cohort design studies, the pooled estimate for the relative vaccine effectiveness of V3 compared with IIV4e for the prevention of influenza-related medical encounters was 13.7% (95% confidence interval: 3.1%–24.2%).
Flucelvax Vaccine Dosage
Flucelvax is a preservative- and latex-free vaccine for intramuscular injection only. It is available as a 0.5ml intramuscular vaccine per dose.
Flucelvax Vaccine Side Effects
CSL Seqirus published a FluCelVax vaccine side effect disclosure in 2016, followed by Australia, and the EMA updated Flucelvax Tetra in 2020. The most common (≥10%) local and systemic reactions in adults 18-64 years of age were injection site pain (45.4%), headache (18.7%), fatigue (17.8%), and myalgia (15.4%), injection site erythema (13.4%), and induration (11.6%), according to the U.S. FDA.
Flucelvax Vaccine News
July 10, 2025 - Stefan Merlo, Vice President of Commercial Operations, North America, CSL Seqirus, stated, "In light of this, we are fully committed to supporting our partners in their efforts to protect the health of their communities by offering a differentiated portfolio of flu vaccines with options designed to provide higher levels of protection compared to traditional vaccines, helping address factors that commonly impact vaccine effectiveness."
July 9, 2024 - CSL Seqirus announced that it has commenced shipping its differentiated portfolio of influenza vaccines.
July 1, 2024 - The U.S. FDA wrote: We hereby approve the draft content of labeling, including the Package Insert submitted on March 28, 2024, and the draft carton and container labels submitted on the same date, as well as under Amendment 2, dated June 3, 2024.
February 8, 2024 - "Influenza continues to cause a significant public health burden, and the agility to rapidly adapt vaccines to match the circulating strains remains paramount. We are proud to say that we have responded swiftly to meet the FDA's directive and are committed to working with health authorities to support this transition ahead of the 2024/25 flu season," said Gregg Sylvester, Chief Health Officer and Head of Medical Affairs, CSL Seqirus.
October 11, 2023 - CSL Seqirus announced new data from three studies supporting the clinical, public health, and economic value of cell-based and adjuvanted seasonal influenza vaccines. The data highlights the effectiveness and value of influenza vaccination in the U.S. across all relevant age groups, risk profiles, and influenza seasons with different levels of influenza burden.
August 15, 2023 - CSL Seqirus reported that FLUCELVAX® sales recently increased by 30%.
July 17, 2023 - CSL Seqirus announced it has begun to ship 55 million cell-based, adjuvanted, and egg-based influenza vaccines across the U.S.
September 26, 2022 - Seqirus published data that "show the benefits of adjuvanted and cell-based influenza vaccine technology advances, like aTIV and QIVc, in reducing influenza-related outcomes compared to high-dose or standard vaccines in the real-world setting," said Dr. Gregg Sylvester, Chief Health Officer
July 11, 2022 - CSL Seqirus announced the shipping of its influenza vaccines for the 2022/23 flu season.
June 6, 2022 - Seqirus announced the completion of an expansion to its manufacturing facility in Holly Springs, N.C., which supports the formulation and fill-finish of cell-based influenza vaccines in pre-filled syringes for global communities. The U.S. FDA-approved manufacturing facility and pre-filled syringe line will allow Seqirus to increase its capacity to supply the U.S. market with FLUCELVAX® QUADRIVALENT vaccines.
June 2, 2022 - Seqirus announced its manufacturing facility in Holly Springs, North Carolina. It has successfully met all the criteria required to establish domestic manufacturing capability for cell-based seasonal and pandemic influenza vaccines, as outlined by the Biomedical Advanced Research and Development Authority (BARDA). Additionally, the joint investment enables Seqirus to sustain the production of differentiated seasonal cell-based influenza vaccines.
October 19, 2021 - Seqirus presented new real-world evidence (RWE) at the International Society for Influenza and Other Respiratory Virus Diseases (ISIRV) global meeting. Most notably, Seqirus' cell-based quadrivalent seasonal influenza vaccine (QIVc) was more effective than standard, egg-based quadrivalent influenza vaccines (QIVe) in reducing influenza-related medical encounters (IRME) in children (aged ≥4 to ≤17) and adults (aged ≥18) during the 2019/20 U.S. influenza season.
October 15, 2021 - New Jersey-based Seqirus announced that the U.S. FDA had approved FLUCELVAX® QUADRIVALENT for an expanded age indication for children as young as six months old.
August 19, 2021 - Seqirus announced plans to accelerate the development of its next-generation messenger RNA (mRNA) vaccine technology, self-amplifying messenger RNA (sa-mRNA), by establishing a dedicated sa-mRNA program. Seqirus is developing several sa-mRNA-based influenza vaccine candidates, with pre-clinical results demonstrating promise compared to more traditional influenza vaccine technologies. The Company targets clinical trials for seasonal and pandemic influenza vaccine candidates in the second half of 2022.
July 30, 2021 - The Flucelvax Quadrivalent Vaccine (QIVc) was safe for pregnant women. "These data provide additional safety information regarding unexpected pregnancy complications and/or fetal outcomes to healthcare providers considering vaccination to protect their pregnant patients from the flu," said Josephine van Boxmeer, lead Clinical Scientist for the study at Seqirus and an author. "We are committed to helping to protect as many people as possible against influenza, including those who are pregnant."
May 3, 2021 - Seqirus-US 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.
March 18, 2021 - Seqirus announced that Health Canada had approved FLUCELVAX® QUADRIVALENT.
March 4, 2021 - Seqirus announced that the U.S. Food and Drug Administration had approved FLUCELVAX® QUADRIVALENT (Influenza Vaccine), the Company's cell-based quadrivalent influenza vaccine (QIVc), for an expanded age indication for people two years of age and older.
December 9, 2020 - Seqirus presented new real-world evidence at the European Scientific Working Group on Influenza 2020 showing the clinical benefits of a cell-based, quadrivalent seasonal influenza vaccine (QIVc) in preventing influenza-related medical encounters compared to an egg-based quadrivalent influenza vaccine (QIVe) during the 2018 - 2019 influenza season.
October 29, 2020 - Seqirus presented absolute efficacy data on the Company's cell-based quadrivalent influenza vaccine (QIVc) from a randomized controlled trial, which met its primary endpoint in children and adolescents between ≥2 <18 years of age over three influenza seasons.
July 30, 2020 - Seqirus announced it has begun shipping its portfolio of seasonal influenza vaccines to customers in the U.S. for the 2020/21 influenza season. Seqirus is one of the world's largest influenza vaccine companies, well-positioned to supply up to 60 million doses to the U.S. market, depending on demand.
Flucelvax Clinical Trials
Seqirus continues to evaluate the Efficacy, Safety, and Immunogenicity of QIVc in clinical trials.
