mFlusiva

mFlusiva (mRNA-1010) is an mRNA-based influenza vaccine used to prevent flu illness in adults ages 50 years and older. It is given as a single injection into a muscle (intramuscular injection) once each flu season. mFlusiva FDA approval was granted on August 5, 2026, and is the first mRNA-based influenza vaccine approved.

mFlusiva works by giving your cells instructions to make specific surface proteins from the three influenza strains in the vaccine. Your cells read those instructions and build harmless copies of the proteins (antigens). Your immune system recognizes them as foreign and builds protection against influenza, so it can respond faster if you encounter the real virus.

mFlusiva does not prevent other respiratory infections, and it may not protect everyone who receives it.

mFlusiva is FDA approved for active immunization against seasonal influenza caused by influenza A and B strains in adults:

• 50 to 64 years (full FDA approval)
• 65 years and older (accelerated FDA approval)

This accelerated approval for the 65-and-over indication is based on immune responses rather than on efficacy outcomes in that age group. Continued approval for this group requires further studies to confirm clinical benefit.

mFlusiva contains mRNA that carries instructions for making the full-length hemagglutinin (HA) surface proteins of the three influenza strains in the vaccine. After the mRNA enters your cells, the cells use it as a template to make those HA proteins. Your immune system recognizes them as foreign and produces an immune response that helps protect against influenza.

The mRNA in mFlusiva encodes proteins that cannot cause influenza. The vaccine stimulates antibodies against the influenza viruses that carry the proteins included in the vaccine.

Antibodies to one influenza virus type or subtype give limited or no protection against another. Antibodies to one antigenic variant may also not protect against a new variant of the same type or subtype. This gradual change, called antigenic drift, is why seasonal flu epidemics occur and why one or more strains in the flu vaccine are usually changed each year.

The 2026-2027 formula of mFlusiva contains three RNAs, 12.5 micrograms of each, for a total of 37.5 micrograms of RNA in each 0.38 mL dose. Each RNA encodes the hemagglutinin glycoprotein of one influenza strain recommended by the FDA for the 2026-2027 season.

Always check that the label on the pre-filled syringe states the 2026-2027 formula before the vaccine is given.

Do not receive mFlusiva if you have had a severe allergic reaction, such as anaphylaxis, to mFlusiva or to any of its ingredients. This is the only contraindication listed in the prescribing information.

Tell your healthcare provider about all of your medical conditions before you receive mFlusiva, particularly if you have allergies, have had Guillain-Barré syndrome after a flu vaccine, have a weakened immune system, are pregnant or breastfeeding, or have ever fainted after an injection.

Specifically, tell your provider if you:

• Have any allergies, or have had a severe allergic reaction after a previous dose of any other vaccine
• Have had Guillain-Barré syndrome (severe muscle weakness) after receiving an influenza vaccine
• Are immunocompromised, or take a medicine that affects your immune response
• Are breastfeeding, pregnant, or plan to become pregnant
• Have ever fainted in connection with an injection

Allergic reactions

Severe allergic reactions are rare but can happen after vaccination. If one occurs, it usually happens within minutes to one hour after the dose. Vaccination sites must have appropriate medical treatment immediately available to manage anaphylaxis, and your provider may ask you to wait for a short time after your injection.

Guillain-Barré syndrome

If Guillain-Barré syndrome (GBS) occurred within 6 weeks of a previous influenza vaccination, the decision to give mFlusiva should be based on careful consideration of the potential benefits and risks.

The 1976 swine influenza vaccine was linked to an increased frequency of GBS. Evidence for a causal link between GBS and other influenza vaccines is inconclusive. If an excess risk exists, it is probably slightly more than one additional case per 1 million people vaccinated.

Fainting

Fainting (syncope) can occur with injectable vaccines including mFlusiva. Procedures should be in place to avoid injury if fainting happens.

Weakened immune system

People who are immunocompromised, including those taking immunosuppressive therapy, may have a reduced immune response to mFlusiva.

The most common mFlusiva side effects are injection site pain, tiredness, headache, muscle pain, joint pain, chills, and underarm swelling or tenderness on the same side as the injection. In clinical trials, most reactions started around 2 days after vaccination, lasted a median of 2 days, and were mild to moderate.

Common side effects by age group

Reactions reported by 10% or more of people in the pivotal trial:

Other reported reactions included nausea or vomiting (9.7% in ages 50 through 64, 7.4% in ages 65 and older), fever (6.0% and 5.6%), injection site swelling or hardness (6.4% and 5.0%), and injection site redness (4.4% and 3.4%).

Solicited reactions of any grade, including Grade 3, were reported more often with mFlusiva than with the standard dose comparator vaccine. Most were Grade 1 or Grade 2 in severity. No Grade 4 solicited local or systemic reactions were reported in this trial.

Serious side effects

In the pivotal trial, serious adverse events over 6 months of follow-up were reported in 2.2% of people who received mFlusiva and 1.9% of people who received the standard dose comparator vaccine. One serious adverse event was assessed as related to the vaccine: fainting on day 2 after vaccination, with fever and possible dehydration, in a 62-year-old participant.

Unsolicited adverse events within 28 days of vaccination were reported in 5.9% of the mFlusiva group and 5.7% of the comparator group. No patterns or numerical imbalances suggesting a causal relationship to mFlusiva were identified.

These may not be all the possible side effects. Ask your healthcare provider about any side effects that concern you. Side effects can be reported to the Vaccine Adverse Event Reporting System (VAERS) at 1-800-822-7967 or at vaers.hhs.gov, or to ModernaTX, Inc. at 1-866-663-3762.

In a Phase 3 trial in adults 50 years and older, the mFlusiva group had 26.6% fewer cases of laboratory-confirmed flu-like illness than the group given a standard dose inactivated flu vaccine. In the trial, 2.0% of people given mFlusiva developed flu-like illness, compared with 2.8% of those given the standard dose vaccine.

In a Phase 3 trial in adults 50 years and older, 2.0% of people given mFlusiva developed laboratory-confirmed flu-like illness, compared with 2.8% of people given a standard dose inactivated flu vaccine. That is 26.6% fewer cases in the mFlusiva group (95% CI 16.7 to 35.4)

Study 1: efficacy in adults 50 years and older

Study 1 (NCT06602024) was a Phase 3, randomized, double-blind, active-controlled trial run during the 2024-2025 influenza season.

Participants received either mFlusiva (20,350 people) or a U.S.-licensed standard dose inactivated influenza vaccine comparator, Fluarix Quadrivalent or Fluarix (20,353 people). People who were immunocompromised or taking immunosuppressive medicines were excluded.

The primary endpoint was RT-PCR-confirmed, protocol-defined influenza-like illness caused by any influenza A or B strain, starting at least 14 days after vaccination through the end of the season. All three pre-specified success criteria were met.

Subtype results were descriptive analyses. Influenza B cases were not distinguished by lineage, and relative efficacy against influenza B could not be precisely estimated because so few cases occurred.

Results by age group

These age subgroup analyses were descriptive. The estimate for people 75 and older is imprecise because of the small number of cases.

Study 2: immune response in adults 65 years and older

Effectiveness in adults 65 and older is based on immunogenicity data from Study 2 (NCT05827978), a randomized, double-blind, active-controlled U.S. trial run during the 2023-2024 influenza season in 2,991 participants.

Study 2 used an unlicensed Moderna mRNA quadrivalent influenza vaccine, made by the same process as mFlusiva and differing only by the addition of the RNA encoding the B/Yamagata antigen. It was compared with a high-dose inactivated influenza vaccine, Fluzone High-Dose Quadrivalent. At the time of the study, the high-dose comparator, but not the standard dose comparator used in Study 1, was one of the influenza vaccines preferentially recommended by the U.S. Centers for Disease Control and Prevention (CDC) for adults 65 and older.

The co-primary endpoints were hemagglutination inhibition (HAI) geometric mean titer (GMT) and seroconversion rate at day 29. All co-primary endpoints were met for every vaccine-matched strain.

An important limitation applies to the B/Victoria result. In Study 1, HAI titers correlated significantly with confirmed influenza-like illness for A/H1N1 and A/H3N2, but the correlation for B/Victoria was not statistically significant. Effectiveness against B/Victoria therefore cannot be reliably inferred from HAI titers.

In Study 2, serious adverse events over 6 months were reported in 2.7% of the mRNA vaccine group and 2.6% of the high-dose comparator group, with none considered causally related to the mRNA vaccine.

mFlusiva is given as a single 0.38 mL dose injected into a muscle (intramuscular injection), usually in the upper arm. Each pre-filled syringe contains one dose and is discarded after single use. Annual influenza vaccination is recommended.

Points your vaccinator will follow before giving the dose:

• Check that the pre-filled syringe label states the 2026-2027 formula.
• Inspect the suspension for particles and discoloration. mFlusiva is white to off-white and may contain visible white or translucent product-related particles. It should not be given if it is discolored or contains other particulate matter.
• Do not shake the syringe.
• Remove the tip cap with the tip pointing up, twisting counterclockwise in a slow, steady motion, without pulling while twisting.
• Attach the needle by twisting clockwise until it is secure.

mFlusiva is not approved for use in anyone younger than 50 years of age. Available data on mFlusiva given to pregnant women are insufficient to inform vaccine-associated risks in pregnancy, and it is not known whether mFlusiva passes into human milk.

In an animal developmental toxicity study, female rats were given a vaccine containing 100 micrograms of nucleoside-modified mRNA, which is 2.7 times the amount in a full human dose, twice before mating and twice during gestation. No vaccine-related fetal malformations or variations were seen, there was no adverse effect on postnatal development, and there was no evidence of impaired female fertility.

For breastfeeding, no human or animal data are available on effects on the breastfed infant or on milk production. The benefits of breastfeeding should be weighed against the mother's clinical need for mFlusiva and any potential effects on the infant.

All pregnancies carry a risk of birth defect, loss, or other adverse outcomes. In the U.S. general population, the estimated background risk of major birth defects is 2% to 4% and of miscarriage is 15% to 20% in clinically recognized pregnancies.

No. The safety and effectiveness of mFlusiva have not been established in anyone younger than 18 years of age, and the vaccine is only approved for people 50 years of age and older.

mFlusiva is approved for adults 65 and older under accelerated approval based on immune response data, with confirmation of clinical benefit still to be assessed in a postmarketing trial. Reported side effect rates were generally lower in this age group than in adults aged 50 through 64.

Of the 20,350 participants aged 50 and older who received mFlusiva in Study 1, 9,726 (47.8%) were 65 and older and 2,354 (11.6%) were 75 and older. Of the 1,502 participants aged 65 and older who received the Moderna mRNA quadrivalent vaccine in Study 2, 326 (21.7%) were 75 and older.

mFlusiva (2026-2027 formula) is supplied as a carton of 10 single-dose pre-filled syringes, each containing one 0.38 mL dose (NDC 80777-500-20; syringe NDC 80777-500-18).

Storage requirements:

• Store refrigerated at 2°C to 8°C (36°F to 46°F). Do not freeze.
• Minimize exposure to room light during storage, and avoid direct sunlight and ultraviolet light.
• mFlusiva may be stored at 8°C to 25°C (46°F to 77°F) for up to 12 hours after removal from the fridge. Discard the syringe if it is not used within that time.
• Do not return syringes to refrigerated storage after they have been kept at room temperature.

Each 0.38 mL dose of mFlusiva contains three mRNAs (12.5 micrograms each, 37.5 micrograms total) encapsulated in lipid nanoparticles, plus the following:

• Total lipid content 0.759 mg, comprising SM-102, polyethylene glycol (PEG) 2000 dimyristoyl glycerol (DMG), cholesterol, and 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC)
• Tromethamine 0.189 mg
• Tromethamine hydrochloride 0.934 mg
• Sucrose 32.6 mg
• Water for injection

mFlusiva does not contain egg protein, antibiotics, or preservatives. The rubber tip cap and plunger of the pre-filled syringe are not made with natural rubber latex.