Flucelvax (Cell-Based Influenza Vaccine)
Quadrivalent inactivated influenza vaccine produced in cell culture for seasonal flu prevention
Flucelvax is a cell culture-based quadrivalent influenza vaccine used to prevent seasonal influenza (flu) in adults and children. Unlike traditional egg-based flu vaccines, Flucelvax is produced using Madin Darby Canine Kidney (MDCK) cell culture technology, which avoids egg-adaptation mutations and may provide improved antigenic match with circulating flu strains. It is administered as a single intramuscular injection annually before or during the flu season.
Quick Facts
Key Takeaways
- Flucelvax is a cell culture-based quadrivalent influenza vaccine that protects against four influenza strains (two A subtypes and two B lineages) each flu season.
- Produced in MDCK cell culture instead of eggs, Flucelvax is egg-free and suitable for individuals with egg allergies, including those with severe egg allergy.
- Clinical studies suggest cell-based influenza vaccines may offer modestly improved effectiveness (approximately 10-11% relative improvement) compared to standard egg-based vaccines.
- The vaccine is approved for individuals aged 2 years and older (EMA) or 6 months and older (FDA), with annual vaccination recommended before or during the flu season.
- Common side effects are generally mild and include injection site pain, headache, fatigue, and muscle pain, typically resolving within 1-3 days.
What Is Flucelvax and What Is It Used For?
Flucelvax (also marketed as Flucelvax Tetra or Flucelvax Quadrivalent) is an inactivated influenza vaccine manufactured by Seqirus. It is designed to provide active immunization against seasonal influenza caused by the four influenza virus strains contained in the vaccine. The vaccine includes two influenza A subtypes (typically H1N1 and H3N2) and two influenza B lineages (Victoria and Yamagata), making it a quadrivalent formulation that offers broad protection against circulating flu viruses.
What distinguishes Flucelvax from most other influenza vaccines is its manufacturing process. Traditional flu vaccines are produced by growing influenza viruses in embryonated chicken eggs, a method that has been used for decades but has known limitations. When influenza viruses replicate in eggs, they can acquire adaptive mutations in the haemagglutinin protein (known as egg-adaptation) that alter the antigenic properties of the vaccine strain. These mutations can reduce the match between the vaccine virus and the actual circulating strains, potentially decreasing vaccine effectiveness.
Flucelvax addresses this limitation by using Madin Darby Canine Kidney (MDCK) cell culture technology for virus propagation. In this process, influenza viruses are grown in mammalian cells rather than eggs, which better preserves the antigenic characteristics of the original wild-type virus. This cell-based approach has been shown in observational studies to improve the antigenic match with circulating strains, which may translate to enhanced protective efficacy. A large-scale retrospective study published in Vaccine (2021) demonstrated an approximately 10-11% relative improvement in vaccine effectiveness of cell-based versus standard egg-based flu vaccines against influenza-related medical encounters.
The vaccine is indicated for the prevention of influenza disease in individuals aged 2 years and older according to European Medicines Agency (EMA) approval, while the U.S. Food and Drug Administration (FDA) has approved its use from 6 months of age. Flucelvax is particularly recommended for individuals at higher risk of influenza complications, including older adults aged 65 and over, individuals with chronic medical conditions (such as diabetes, heart disease, chronic lung disease, or immunocompromising conditions), pregnant women, and healthcare workers. However, any eligible individual can receive the vaccine as part of routine seasonal influenza vaccination.
Influenza remains a major global public health concern, causing an estimated 3 to 5 million cases of severe illness and 290,000 to 650,000 respiratory deaths annually worldwide according to the World Health Organization. Annual vaccination is the most effective strategy for preventing influenza and its complications, and cell-based vaccines like Flucelvax represent a modern advancement in vaccine technology that aims to improve upon the protection offered by traditional egg-based vaccines.
What Should You Know Before Receiving Flucelvax?
Contraindications
Flucelvax is contraindicated in individuals who have experienced a severe allergic reaction (such as anaphylaxis) to a previous dose of any influenza vaccine or to any excipient contained in the vaccine formulation. This includes hypersensitivity to the active substances, to any of the excipients, or to residual manufacturing substances such as beta-propiolactone, cetyltrimethylammonium bromide (CTAB), or polysorbate 80.
It is important to note that Flucelvax does not contain egg protein (ovalbumin) and is therefore considered safe for individuals with egg allergies, including those with a history of severe egg allergy or anaphylaxis to egg. This is a significant advantage over traditional egg-based influenza vaccines, which may contain trace amounts of egg protein. Both the American College of Allergy, Asthma, and Immunology (ACAAI) and the CDC Advisory Committee on Immunization Practices (ACIP) recognize cell-based and recombinant influenza vaccines as options for egg-allergic individuals.
Appropriate medical treatment and supervision must always be readily available in case of an anaphylactic reaction following administration of the vaccine. As with all injectable vaccines, Flucelvax should be administered in a setting where emergency equipment and medications are immediately available.
Warnings and Precautions
Vaccination should be postponed in individuals suffering from acute severe febrile illness or acute infection. The presence of a minor infection or low-grade fever should not normally delay vaccination, but the decision should be made by the administering healthcare professional based on clinical judgment.
As with all injectable vaccines, there is a small risk of syncope (fainting), particularly in adolescents and young adults. Appropriate precautions should be taken to avoid injury from fainting, and the recipient should be observed for approximately 15 minutes after vaccination. Individuals who have experienced Guillain-Barré syndrome (GBS) within 6 weeks of a previous influenza vaccination should discuss the risks and benefits of vaccination with their healthcare provider, as there is a small potential for recurrence.
The immune response to Flucelvax may be diminished in individuals receiving immunosuppressive therapy, including high-dose corticosteroids, chemotherapy, or biologic agents. For these patients, the timing of vaccination relative to immunosuppressive treatment should be discussed with their treating physician. Patients with congenital or acquired immunodeficiency may have a reduced immune response but should still generally be vaccinated, as the potential benefits outweigh the risks.
Flucelvax, like all influenza vaccines, may not fully protect all vaccinated individuals. Vaccine effectiveness varies from season to season depending on the match between vaccine strains and circulating viruses, the age and health status of the recipient, and other factors. Protection typically develops within 2 to 3 weeks after vaccination.
Pregnancy and Breastfeeding
Influenza vaccination is recommended during pregnancy by the World Health Organization, the CDC, and numerous national immunization programs worldwide. Pregnant women are at increased risk of severe influenza complications, and vaccination protects both the mother and the newborn infant through transplacental antibody transfer. Extensive safety data from the use of inactivated influenza vaccines during pregnancy support their safety profile.
While specific clinical trial data for Flucelvax during pregnancy are limited, the vaccine is an inactivated formulation and is not expected to pose any risk to the developing fetus. Healthcare providers should weigh the benefits of vaccination against the theoretical risks based on individual patient circumstances. Inactivated influenza vaccines can also be administered during breastfeeding, as they do not affect the safety of breast milk or the breastfed infant.
How Does Flucelvax Interact with Other Drugs?
Drug interactions with Flucelvax are generally limited because the vaccine is an inactivated biological product rather than a systemic pharmaceutical agent. However, certain medications and therapies can influence the immune response to vaccination, and these should be considered when planning vaccination schedules.
Flucelvax may be given at the same time as other inactivated or live vaccines, provided that different injection sites are used and the vaccines are not mixed in the same syringe. Clinical studies have evaluated the co-administration of Flucelvax with COVID-19 mRNA vaccines and have demonstrated acceptable immunogenicity and safety profiles when both vaccines are administered concurrently. This is particularly relevant during autumn vaccination campaigns when both influenza and COVID-19 vaccines may be offered simultaneously.
Major Interactions
| Drug/Therapy | Effect | Clinical Significance |
|---|---|---|
| High-dose corticosteroids | May significantly reduce antibody response to vaccine | Consider timing vaccination when immunosuppression is minimal; discuss with prescribing physician |
| Chemotherapy agents | Substantially diminished immune response | Vaccinate at least 2 weeks before starting chemotherapy or between treatment cycles when possible |
| Anti-CD20 monoclonal antibodies (e.g., rituximab, ocrelizumab) | Profoundly impaired B-cell mediated antibody response | Vaccinate at least 4-6 months after last dose if possible; response may still be attenuated |
| Organ transplant immunosuppressants | Reduced but not eliminated immune response | Vaccination still recommended; may require higher-dose or adjuvanted vaccine alternatives |
Minor Interactions
| Drug/Therapy | Effect | Clinical Significance |
|---|---|---|
| Warfarin and anticoagulants | Rare reports of altered INR following influenza vaccination | Monitor INR more closely for 1-2 weeks after vaccination in patients on warfarin; generally safe to administer |
| NSAIDs and paracetamol | No clinically significant impact on vaccine immunogenicity | Can be used for post-vaccination symptom relief; prophylactic use not routinely recommended |
| Other inactivated vaccines | No interference when given at different injection sites | Safe for co-administration; commonly given alongside COVID-19, pneumococcal, and other vaccines |
It is always advisable to inform your healthcare provider about all medications you are taking, including prescription drugs, over-the-counter medicines, herbal supplements, and other vaccines you have recently received or plan to receive. This helps ensure optimal vaccination timing and appropriate monitoring.
What Is the Correct Dosage of Flucelvax?
Flucelvax is supplied as a pre-filled syringe containing 0.5 mL of suspension for injection. Each 0.5 mL dose contains 15 micrograms of haemagglutinin from each of the four influenza virus strains included in the vaccine (60 micrograms total). The vaccine is administered by intramuscular injection, preferably into the deltoid muscle of the upper arm in adults and older children, or into the anterolateral thigh in younger children.
Adults
Adults (18 years and older)
One dose of 0.5 mL administered as a single intramuscular injection annually. No booster dose is required. Vaccination should ideally occur before the start of the influenza season, typically in October or November in the Northern Hemisphere and April to May in the Southern Hemisphere. However, vaccination can be administered throughout the influenza season.
Children
Children and Adolescents (9-17 years)
One dose of 0.5 mL administered as a single intramuscular injection annually.
Children (2-8 years, EMA approval / 6 months to 8 years, FDA approval)
Children who have been previously vaccinated against influenza: one dose of 0.5 mL. Children who are being vaccinated against influenza for the first time: two doses of 0.5 mL administered at least 4 weeks apart. For children aged 6 to 35 months (FDA approval), the same 0.5 mL dose is administered. The second dose ensures adequate immune priming in immunologically naive children.
Elderly
Older Adults (65 years and older)
One dose of 0.5 mL administered as a single intramuscular injection annually. No dose adjustment is necessary. However, it should be noted that immune responses may be lower in elderly individuals due to immunosenescence. In some jurisdictions, enhanced influenza vaccines (such as high-dose or adjuvanted formulations) may be preferentially recommended for this age group. Healthcare providers should follow local vaccination guidelines and recommendations.
| Age Group | Dose | Number of Doses | Route |
|---|---|---|---|
| 6-35 months (FDA only) | 0.5 mL | 1 or 2* | Intramuscular (anterolateral thigh) |
| 2-8 years | 0.5 mL | 1 or 2* | Intramuscular (deltoid or thigh) |
| 9-17 years | 0.5 mL | 1 | Intramuscular (deltoid) |
| 18-64 years | 0.5 mL | 1 | Intramuscular (deltoid) |
| 65+ years | 0.5 mL | 1 | Intramuscular (deltoid) |
* Two doses (given at least 4 weeks apart) for children being vaccinated against influenza for the first time.
Missed Dose
Because Flucelvax is typically given as a single annual dose, the concept of a missed dose is somewhat different from daily medications. If you have not received your annual influenza vaccination, it is still beneficial to get vaccinated later in the flu season, even into January or February in the Northern Hemisphere. For children requiring two doses who miss the second dose, it should be administered as soon as possible; restarting the series is not necessary.
Overdose
Cases of overdose with Flucelvax have not been reported as a significant clinical concern, given that the vaccine is administered as a single pre-measured dose by healthcare professionals. However, if an inadvertent overdose occurs (such as administration of more than one dose in a short period), the recipient should be monitored for any adverse effects. There is no specific antidote. In the event of overdose, symptomatic treatment should be provided as needed. Reports from post-marketing surveillance have not identified specific safety concerns from inadvertent additional doses of influenza vaccine.
What Are the Side Effects of Flucelvax?
Like all vaccines, Flucelvax can cause side effects, although not everybody experiences them. The majority of side effects are mild to moderate in severity and are self-limiting, typically resolving within 1 to 3 days without treatment. These reactions are generally indicative of the immune system responding to the vaccine and mounting a protective response. Clinical trials involving thousands of participants have established the following side effect profile.
Very Common
- Injection site pain and tenderness
- Headache
- Fatigue and malaise
- Myalgia (muscle pain)
- Injection site erythema (redness)
- Injection site induration (hardness)
Common
- Injection site swelling
- Arthralgia (joint pain)
- Nausea
- Chills
- Fever (temperature ≥38°C / 100.4°F)
- Injection site bruising (ecchymosis)
Uncommon
- Dizziness
- Lymphadenopathy (swollen lymph nodes)
- Diarrhoea
- Vomiting
- Pruritus (itching) at injection site
- Rash
Rare
- Anaphylaxis or severe allergic reaction
- Guillain-Barré syndrome (GBS)
- Neuralgia
- Paraesthesia (tingling or numbness)
- Convulsions (febrile seizures, primarily in children)
- Vasculitis (inflammation of blood vessels)
Injection site reactions are the most frequently reported side effects, with pain at the injection site occurring in more than half of all recipients in clinical trials. These local reactions are typically mild and resolve spontaneously within 1-2 days. Systemic reactions such as headache, fatigue, and myalgia are also common but are generally of short duration.
Fever is more commonly observed in children than in adults following vaccination. In paediatric clinical trials, fever was reported in approximately 5-10% of children aged 2-8 years, compared to approximately 1-2% of adults. Parents should be informed that mild fever is a normal immune response and can be managed with age-appropriate antipyretic medications such as paracetamol (acetaminophen) or ibuprofen if needed.
Serious adverse events following Flucelvax are extremely rare. Anaphylactic reactions can occur with any vaccine but are estimated to occur at a rate of approximately 1 per million doses for influenza vaccines. Guillain-Barré syndrome has been reported very rarely following influenza vaccination, with an estimated attributable risk of approximately 1-2 additional cases per million vaccinated individuals. The benefits of influenza vaccination greatly outweigh these very small risks for the vast majority of individuals.
Seek immediate medical attention if you experience signs of a severe allergic reaction after vaccination, including difficulty breathing, swelling of the face or throat, rapid heartbeat, dizziness, or a widespread rash. Contact your healthcare provider if injection site reactions worsen after 3 days, if you develop a high fever (>39°C / 102.2°F), or if you experience unusual symptoms such as numbness, tingling, or muscle weakness in the weeks following vaccination.
How Should You Store Flucelvax?
Proper storage of Flucelvax is essential to maintain the vaccine's potency and safety. The vaccine must be stored in a refrigerator at a temperature between 2°C and 8°C (36°F and 46°F) at all times. It should be kept in the original packaging to protect it from light. The pre-filled syringe should be stored in the horizontal position to minimize the time needed to resuspend the contents before administration.
Do not freeze Flucelvax. If the vaccine has been accidentally frozen, it must be discarded and should not be administered. Freezing causes irreversible damage to the vaccine antigens and may significantly reduce its immunogenicity and effectiveness. Even if the vaccine appears normal after thawing, the structural integrity of the antigens may have been compromised.
The vaccine should be allowed to reach room temperature before administration and should be gently shaken to obtain a homogeneous suspension. After removal from the refrigerator, the vaccine should be used promptly. The appearance of the vaccine should be inspected visually before administration; it should be a clear to slightly opalescent liquid. If discolouration or particulate matter is observed, the vaccine should not be used.
Flucelvax should not be used after the expiry date stated on the label and carton. The expiry date refers to the last day of that month. Healthcare facilities should follow proper vaccine storage and handling protocols, including maintaining temperature logs, using calibrated thermometers, and implementing first-in-first-out (FIFO) inventory management. Any vaccine that has been improperly stored should be quarantined and assessed according to local public health guidelines before use or disposal.
Patients do not typically store Flucelvax at home, as it is administered by healthcare professionals in clinical settings. However, if transport is necessary, the vaccine should be kept in an insulated container with appropriate cold packs to maintain the recommended temperature range, taking care that the vaccine does not come into direct contact with ice or freezing elements.
What Does Flucelvax Contain?
Each 0.5 mL dose of Flucelvax Quadrivalent contains 15 micrograms of haemagglutinin from each of four influenza virus strains, for a total of 60 micrograms of haemagglutinin. The four strains are updated annually based on World Health Organization recommendations to match the influenza viruses predicted to circulate in the upcoming season. Typically, the vaccine includes two influenza A strains (an A/H1N1 and an A/H3N2 subtype) and two influenza B strains (one from each of the B/Victoria and B/Yamagata lineages).
The active substance consists of purified surface antigens—specifically, the haemagglutinin and neuraminidase glycoproteins—obtained from influenza virus grown in MDCK (Madin Darby Canine Kidney) cell culture. The viruses are propagated in these mammalian cells, harvested, inactivated with beta-propiolactone, and then the surface antigens are purified using a detergent-based splitting process. This cell-based manufacturing process is a key differentiator from traditional egg-based vaccines.
Excipients (Inactive Ingredients)
- Sodium chloride – tonicity agent to make the solution isotonic
- Potassium chloride – buffer component
- Magnesium chloride hexahydrate – stabilizer
- Disodium hydrogen phosphate dihydrate – buffer to maintain pH
- Potassium dihydrogen phosphate – buffer component
- Water for injections – solvent
Residual manufacturing substances present in trace amounts may include beta-propiolactone (used for virus inactivation) and cetyltrimethylammonium bromide (CTAB, used in the purification process). These substances are present at levels far below those that could cause any adverse effects.
Flucelvax in its pre-filled syringe presentation does not contain: egg protein (ovalbumin), thimerosal (mercury-based preservative), latex (in the syringe tip cap), gelatin, formaldehyde, or live virus. The absence of egg protein makes it particularly suitable for individuals with egg allergies. The vaccine is non-replicating and cannot cause influenza infection.
Frequently Asked Questions About Flucelvax
Flucelvax is manufactured using Madin Darby Canine Kidney (MDCK) cell culture technology rather than embryonated chicken eggs. This cell-based production method avoids egg-adaptation mutations that can reduce vaccine effectiveness, and the vaccine is suitable for individuals with egg allergies. Clinical studies suggest cell-based flu vaccines may provide modestly improved protection compared to standard egg-based vaccines due to better antigenic match with circulating strains. The vaccine contains no egg protein whatsoever.
Flucelvax Quadrivalent is approved for active immunization against influenza in individuals aged 2 years and older (EMA) or 6 months and older (FDA). It is particularly recommended for those at high risk of influenza complications, including the elderly, individuals with chronic medical conditions, pregnant women, and healthcare workers. It is also an excellent option for people with egg allergies who need influenza vaccination.
Clinical trials demonstrate that Flucelvax produces robust immunogenic responses comparable to or exceeding those of standard egg-based influenza vaccines. Real-world studies have shown relative vaccine effectiveness improvements of approximately 10-11% compared to standard egg-based vaccines for preventing influenza-related medical encounters. Effectiveness varies by season depending on the match between vaccine strains and circulating viruses, and may range from approximately 40-60% in a typical season.
Yes, Flucelvax can generally be co-administered with other inactivated vaccines at different injection sites. Studies have demonstrated safe co-administration with COVID-19 vaccines. However, immunosuppressive therapies may reduce the immune response to Flucelvax. Always consult your healthcare provider about scheduling multiple vaccinations to ensure optimal immune responses.
No. Flucelvax is manufactured entirely using cell culture technology (MDCK cells) and does not use eggs at any stage of production. It contains no egg protein (ovalbumin) and is considered safe for individuals with egg allergies, including those with a history of severe egg allergy. This makes it a preferred option for egg-allergic individuals requiring influenza vaccination.
Flucelvax is given once annually before or during the influenza season, typically in autumn. Adults and children over 9 years receive a single 0.5 mL dose. Children aged 2-8 years (EMA) or 6 months to 8 years (FDA) who are being vaccinated for the first time may require two doses given 4 weeks apart. Annual revaccination is necessary because the vaccine composition is updated each year to match circulating influenza strains, and immunity wanes over time.
References
- European Medicines Agency (EMA). Flucelvax Tetra – Summary of Product Characteristics. Available at: ema.europa.eu. Accessed January 2026.
- U.S. Food and Drug Administration (FDA). Flucelvax Quadrivalent – Prescribing Information. Available at: fda.gov. Accessed January 2026.
- World Health Organization (WHO). Influenza (Seasonal) Fact Sheet. Available at: who.int. Accessed January 2026.
- Bruxvoort KJ, et al. Comparison of vaccine effectiveness against influenza hospitalization of cell-based and egg-based influenza vaccines, 2017-2018. Vaccine. 2019;37(39):5807-5811. doi:10.1016/j.vaccine.2019.08.024
- Izurieta HS, et al. Relative effectiveness of cell-cultured and egg-based influenza vaccines among elderly persons in the United States, 2017-2018. J Infect Dis. 2019;220(8):1255-1264. doi:10.1093/infdis/jiz265
- Grohskopf LA, et al. Prevention and Control of Seasonal Influenza with Vaccines: Recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR Recomm Rep. 2024;73(5):1-25.
- Barr IG, et al. Cell culture-derived influenza vaccines in the severe 2017-2018 epidemic season: a step towards improved influenza vaccine virus selection. NPJ Vaccines. 2018;3:44. doi:10.1038/s41541-018-0079-z
- Belongia EA, et al. Variable influenza vaccine effectiveness by subtype: a systematic review and meta-analysis of test-negative design studies. Lancet Infect Dis. 2016;16(8):942-951.
- British National Formulary (BNF). Influenza vaccine. Available at: bnf.nice.org.uk. Accessed January 2026.
- European Centre for Disease Prevention and Control (ECDC). Seasonal influenza vaccination and antiviral use in EU/EEA Member States. Technical report, 2023.
Editorial Team
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