Spikevax XBB.1.5: Uses, Dosage & Side Effects
A variant-adapted mRNA COVID-19 vaccine targeting the SARS-CoV-2 Omicron XBB.1.5 subvariant to protect against symptomatic infection and severe disease
Spikevax XBB.1.5 is a variant-adapted messenger RNA (mRNA) COVID-19 vaccine developed by Moderna. It contains elasomeran, a nucleoside-modified mRNA encoding the full-length spike glycoprotein of the SARS-CoV-2 Omicron XBB.1.5 subvariant, encapsulated in lipid nanoparticles. The vaccine is administered as an intramuscular injection and is used for active immunization against symptomatic COVID-19 and severe disease in adults, adolescents, and children aged 6 months and older. Spikevax XBB.1.5 was authorized by the European Medicines Agency (EMA) and the U.S. Food and Drug Administration (FDA) to provide updated protection against circulating Omicron descendant lineages and replaces earlier monovalent and bivalent formulations. The vaccine is administered by trained healthcare professionals in vaccination centers, pharmacies, and clinics.
Quick Facts: Spikevax XBB.1.5
Key Takeaways
- Spikevax XBB.1.5 is a monovalent variant-adapted mRNA vaccine that trains the immune system to recognize the spike protein of the SARS-CoV-2 Omicron XBB.1.5 subvariant, producing neutralizing antibodies and T-cell responses that protect against symptomatic and severe COVID-19.
- It is authorized for individuals aged 6 months and older and can be used either as a primary vaccination series in those who have never been vaccinated or, more commonly, as a booster dose to restore protection that has waned since a previous vaccination or infection.
- The most frequent side effects are mild and transient: injection-site pain, fatigue, headache, muscle pain, chills, fever, and swollen lymph nodes; serious adverse events such as anaphylaxis and myocarditis are rare but recognized risks.
- Pregnant and breastfeeding individuals can safely receive Spikevax XBB.1.5; vaccination during pregnancy reduces the risk of severe COVID-19 and provides passive antibody protection to newborns via the placenta and breast milk.
- Anyone with a known severe allergy to a previous dose of an mRNA COVID-19 vaccine, to polyethylene glycol (PEG), or to any other component of the vaccine should not receive Spikevax XBB.1.5 without specialist evaluation.
What Is Spikevax XBB.1.5 and What Is It Used For?
Spikevax XBB.1.5 is the brand name for the Moderna monovalent variant-adapted COVID-19 vaccine targeting the SARS-CoV-2 Omicron XBB.1.5 subvariant. It belongs to the class of messenger RNA (mRNA) vaccines, a modern vaccine platform that uses a short, synthetic copy of genetic instructions to teach cells in the body how to produce a harmless fragment of the virus. This fragment is the spike glycoprotein, the same protein the real virus uses to attach to and enter human cells. By presenting the spike protein to the immune system without ever introducing the virus itself, mRNA vaccines trigger protective immunity without causing disease.
Spikevax XBB.1.5 was developed as part of the global effort to keep COVID-19 vaccines aligned with circulating SARS-CoV-2 variants. After the original wild-type strain, the virus evolved through successive variants of concern – Alpha, Beta, Delta, and then the Omicron family. By 2023, the Omicron XBB.1.5 subvariant had become dominant in many regions worldwide, and the World Health Organization (WHO) Technical Advisory Group on COVID-19 Vaccine Composition recommended that updated vaccines target this lineage. Moderna subsequently produced the XBB.1.5 monovalent formulation, which received authorization from the EMA, FDA, MHRA, Swissmedic, and numerous other regulatory agencies.
The vaccine is intended for active immunization, meaning it stimulates the recipient’s own immune system to mount a defense against the virus. It is not a treatment for established COVID-19 infection. Once administered, it takes approximately 10 to 14 days for protective antibody levels to develop, with peak neutralizing titers typically reached around 28 days after injection.
Spikevax XBB.1.5 is approved for the following indications:
- Primary vaccination: For individuals aged 6 months and older who have not previously been vaccinated against COVID-19. Infants and young children typically receive a multi-dose primary series, while most older individuals receive a single primary dose under current recommendations.
- Booster doses: For individuals aged 6 months and older who have previously completed a primary series or received prior booster doses of any authorized COVID-19 vaccine. A single dose of Spikevax XBB.1.5 serves as a booster, restoring protection that has declined over time.
- Immunocompromised individuals: People with moderately or severely compromised immune systems (e.g., transplant recipients, patients on immunosuppressive therapy, advanced HIV) may be recommended additional doses to achieve adequate protection, following national or institutional guidance.
While the vaccine is specifically adapted to the XBB.1.5 spike protein, clinical immunogenicity data demonstrate that it elicits cross-reactive neutralizing antibodies against related Omicron descendant lineages, including BA.2.86, JN.1, and other subvariants that evolved from the XBB lineage. This cross-protection is important because SARS-CoV-2 continues to evolve and the specific XBB.1.5 subvariant may no longer be dominant by the time a person is vaccinated. Real-world effectiveness studies have consistently shown that updated vaccines reduce the risk of symptomatic disease, emergency department visits, hospitalization, and death from contemporary circulating variants.
Hundreds of millions of doses of mRNA COVID-19 vaccines have been administered globally since their introduction in December 2020. This unprecedented volume of use, together with comprehensive post-marketing surveillance, makes the safety profile of the Spikevax platform among the most thoroughly characterized of any vaccine in history. Variant-adapted formulations such as Spikevax XBB.1.5 retain the same lipid nanoparticle delivery system and manufacturing process as the original vaccine, with only the coding sequence of the mRNA changed to reflect the updated target strain.
When Spikevax XBB.1.5 is injected into the muscle, the lipid nanoparticles deliver the mRNA payload into nearby cells. The cellular machinery reads the mRNA and produces copies of the spike protein, which are then displayed on the cell surface. Immune cells recognize these proteins as foreign and generate a multi-layered response: neutralizing antibodies that block viral entry, and T-cells that destroy infected cells. The mRNA itself is broken down within days by normal cellular processes and never enters the cell nucleus or interacts with DNA.
What Should You Know Before Receiving Spikevax XBB.1.5?
Contraindications
Spikevax XBB.1.5 must not be administered in the following situations:
- Hypersensitivity: A known history of severe allergic reaction (anaphylaxis) to the active substance (elasomeran) or to any excipient in the vaccine, including lipid nanoparticle components, polyethylene glycol (PEG), trometamol, sodium acetate, acetic acid, or sucrose.
- Severe reaction to a previous dose: Individuals who experienced anaphylaxis after a prior dose of Spikevax or another mRNA COVID-19 vaccine (such as Comirnaty) should not receive further doses without specialist allergy evaluation.
Warnings and Precautions
Cases of myocarditis (inflammation of the heart muscle) and pericarditis (inflammation of the lining around the heart) have been reported following mRNA COVID-19 vaccination. These events are rare, typically occur within 14 days after vaccination (most commonly after the second dose in a primary series), and are observed more frequently in adolescent and young adult males. Symptoms include new chest pain, shortness of breath, or palpitations. Seek immediate medical attention if any of these symptoms occur. Most reported cases have been mild and resolved with standard treatment, but rare serious outcomes have occurred.
Before receiving Spikevax XBB.1.5, inform your healthcare provider if any of the following apply to you:
- Severe allergies: A history of severe allergic reactions to any vaccine, medication, food, or other substance, particularly anaphylaxis requiring emergency treatment. Vaccination centers should maintain emergency medical equipment and trained personnel to manage anaphylaxis should it occur.
- Polyethylene glycol (PEG) allergy: PEG is a component of the lipid nanoparticle system. A documented PEG allergy is an absolute contraindication. Individuals with unclear histories of PEG allergy should undergo specialist allergy assessment.
- Bleeding disorders or anticoagulant therapy: Because the vaccine is given by intramuscular injection, bleeding or bruising at the injection site can occur. Patients with hemophilia or those taking anticoagulants (such as warfarin, direct oral anticoagulants, or heparin) may benefit from a smaller-gauge needle and prolonged pressure applied after injection.
- Weakened immune system: People with compromised immunity due to disease (such as HIV, cancer, primary immunodeficiency) or treatment (such as chemotherapy, high-dose corticosteroids, biologic agents, or following organ transplantation) may have a reduced antibody response to the vaccine. Additional doses may be recommended.
- Fever or acute illness: If you have a significant acute illness with fever, vaccination may be postponed until you recover. Minor illnesses such as a cold or low-grade fever do not typically require postponement.
- History of myocarditis or pericarditis: If you have previously experienced myocarditis or pericarditis after an mRNA COVID-19 vaccine, discuss the risks and benefits of further vaccination with a cardiologist or immunization specialist before receiving additional doses.
- Stress-related reactions: Fainting (vasovagal syncope), dizziness, hyperventilation, or anxiety reactions can occur in association with any injection, particularly in adolescents. You should be seated or observed during and immediately after vaccination.
- History of capillary leak syndrome: Very rare cases of capillary leak syndrome recurrences have been reported. Individuals with a known history of this condition should discuss vaccination with a specialist.
As with all vaccines, Spikevax XBB.1.5 may not protect every recipient. No vaccine offers 100% efficacy, and breakthrough infections can occur. However, vaccinated individuals who do develop COVID-19 generally experience milder illness and are less likely to require hospitalization or die compared with unvaccinated individuals.
Other Medications and Vaccines
Tell your healthcare provider about all medications, herbal products, and supplements you are taking. Spikevax XBB.1.5 can be co-administered with most other vaccines, including seasonal influenza vaccines, pneumococcal vaccines, and recombinant zoster vaccines, although administration on separate visits or into different arms is sometimes preferred to help attribute any adverse reactions. Medications that suppress the immune system (chemotherapy, high-dose corticosteroids, biologics) may reduce the effectiveness of vaccination.
Pregnancy and Breastfeeding
Extensive real-world data now exist on the use of mRNA COVID-19 vaccines during pregnancy. Studies involving hundreds of thousands of vaccinated pregnant individuals have shown no increased risk of miscarriage, stillbirth, preterm birth, or congenital abnormalities. In contrast, SARS-CoV-2 infection during pregnancy is associated with elevated risks of severe maternal illness, intensive care admission, preterm delivery, and stillbirth. International guidelines from the WHO, CDC, ACOG, RCOG, and FIGO recommend COVID-19 vaccination during pregnancy at any gestational age.
Spikevax XBB.1.5 is considered compatible with pregnancy. Vaccination during pregnancy offers two-fold protection: it reduces the risk of COVID-19-related complications in the pregnant person, and it provides passive antibody protection to the newborn through transplacental antibody transfer. Neonates born to vaccinated mothers have measurable anti-spike antibody levels at birth that can help protect them during the first months of life.
Breastfeeding is not a contraindication to Spikevax XBB.1.5. Antibodies produced in response to the vaccine pass into breast milk and may provide additional passive protection to breastfed infants. The vaccine components (mRNA and lipid nanoparticles) are not meaningfully transferred into breast milk in clinically relevant amounts, and any trace amounts would be degraded in the infant’s digestive system.
Driving and Operating Machinery
Spikevax XBB.1.5 has no known direct effect on the ability to drive or operate machinery. However, some side effects such as fatigue, dizziness, or malaise may temporarily affect performance. If you experience these symptoms, refrain from driving or operating machinery until they resolve.
Important Information About Ingredients
Spikevax XBB.1.5 contains small amounts of sodium (less than 1 mmol per dose), so it is considered “sodium-free” for dietary purposes. It contains no preservatives such as thiomersal, and it is not derived from animal products or blood. The manufacturing process does not use human fetal cells or animal tissues, and the final product contains no gelatin, egg, or latex.
How Does Spikevax XBB.1.5 Interact with Other Drugs?
Spikevax XBB.1.5 does not enter the bloodstream as a systemic drug and does not interact with drug-metabolizing enzymes such as cytochrome P450 in the liver. However, clinically meaningful interactions can still occur, particularly with medications that modify immune function or coagulation. It is essential to inform your vaccinator about all medications you are taking, including over-the-counter products, herbal supplements, and recent vaccinations.
Major Interactions
| Interacting Drug | Effect | Clinical Significance |
|---|---|---|
| High-dose corticosteroids (e.g., prednisone ≥20 mg/day >14 days) | May blunt vaccine-induced antibody response | Consider timing vaccination before initiation or during dose reduction; additional doses may be needed |
| Chemotherapy / cytotoxic agents | Significantly reduced vaccine efficacy during active treatment | Vaccinate before chemotherapy if possible; additional booster doses often recommended |
| B-cell depleting therapies (rituximab, ocrelizumab, ofatumumab) | Markedly reduced humoral response for 6–12 months after infusion | Ideally vaccinate ≥4 weeks before dose or time carefully; T-cell response may still provide some protection |
| Anticoagulants (warfarin, DOACs, heparin) | Increased risk of injection-site bruising or hematoma | Use fine-gauge needle (25G or 23G); apply firm pressure for 2–5 minutes; no need to stop anticoagulants |
Minor Interactions
| Interacting Drug or Vaccine | Effect | Clinical Significance |
|---|---|---|
| Seasonal influenza vaccine | Safe co-administration; modest increase in reactogenicity | Can be given on the same day in different arms; no loss of efficacy |
| Pneumococcal, zoster, and routine adult vaccines | No clinically significant interaction demonstrated | Co-administration is generally acceptable per WHO and CDC guidance |
| Calcineurin inhibitors (tacrolimus, ciclosporin) | Reduced antibody response in transplant recipients | Additional doses often recommended; consider serologic monitoring |
| Methotrexate, TNF inhibitors, JAK inhibitors | Variable, often modest reduction in antibody titers | Continue therapy but consider temporary interruption of methotrexate around vaccination per rheumatology guidelines |
| Paracetamol, ibuprofen (prophylactic, pre-dose) | Small, not clinically significant reduction in antibody titers | Do not take prophylactically, but use as needed for post-vaccination symptoms |
It is important to note that the vaccine does not cause SARS-CoV-2 infection and cannot produce a false-positive result on SARS-CoV-2 nucleic acid amplification (PCR) or antigen tests, which detect the virus itself. However, the vaccine will cause antibody tests for anti-spike antibodies to become positive. Antibody tests that detect antibodies against the nucleocapsid (anti-N) protein remain negative after vaccination and can therefore distinguish vaccine-induced from infection-induced immunity.
What Is the Correct Dosage of Spikevax XBB.1.5?
Spikevax XBB.1.5 is always administered as an intramuscular injection by a trained healthcare professional. In adults and older children, the preferred site is the deltoid muscle of the upper arm. In infants and young children aged 6 to 23 months, the anterolateral thigh muscle (vastus lateralis) is used. The vaccine must never be given intradermally, subcutaneously, or intravenously. Strict aseptic technique is used at every step of preparation and administration.
The specific dose, schedule, and number of doses depend on the individual’s age, vaccination history, and immune status. Current recommendations vary by country and are updated periodically as evidence evolves. The dosing information below reflects the EMA and FDA authorized indications at the time of writing and should be interpreted in the context of local national or regional guidance.
Adults (18 Years and Older)
Adults — Booster or Single Primary Dose
Dose: 50 μg (0.5 mL) as a single intramuscular injection
Indication: Booster dose for previously vaccinated individuals; single primary dose for those who have never been vaccinated (many national programs now consider a single dose adequate for immunocompetent adults because most have some prior immunity from vaccination, infection, or both).
Site: Deltoid muscle of the non-dominant arm (or either arm if both are equally preferred)
Repeat doses: Annual or seasonal boosting is recommended for high-risk groups (age ≥65, immunocompromised, chronic medical conditions, pregnancy, residents of long-term care facilities, healthcare workers)
Adolescents (12–17 Years)
Adolescents — Booster or Primary Dose
Dose: 50 μg (0.5 mL) intramuscular injection, identical to the adult dose
Indication: Primary vaccination or booster dose in adolescents, particularly those with underlying medical conditions, chronic illness, or increased exposure risk
Special considerations: Young males receiving mRNA COVID-19 vaccines have a slightly higher reported risk of myocarditis than other groups. A single dose rather than a multi-dose primary series is often preferred in immunocompetent healthy adolescents
Children (6 Months–11 Years)
Children Aged 6 Months to 11 Years
Dose: 25 μg (0.25 mL) intramuscular injection (half the adult dose)
Primary series for previously unvaccinated: Two doses 4 weeks apart for healthy children; three doses (weeks 0, 4, and 8) for immunocompromised children
Booster dose: Single 25 μg dose at least 2 months after the last previous dose, per national guidance
Injection site: Anterolateral thigh muscle for infants; deltoid muscle for older children
Elderly (65 Years and Older)
Older Adults
Dose: 50 μg (0.5 mL) intramuscular injection — same as the adult dose
Priority booster schedule: Annual or twice-yearly boosting is strongly recommended, particularly for individuals aged 75 and older, residents of long-term care facilities, and those with chronic medical conditions
Rationale: Older adults remain at highest risk of severe COVID-19, hospitalization, and death; vaccine-induced immunity wanes faster in this group
Immunocompromised Individuals
Moderately to Severely Immunocompromised Persons
Dose: 50 μg (0.5 mL) for age 12+; 25 μg (0.25 mL) for 6 months–11 years
Extended schedule: National guidelines typically recommend an extended primary series (three doses at 0, 4, and 8 weeks) followed by boosters every 6 months or as clinically indicated
Groups considered immunocompromised: Active cancer treatment, solid organ or stem cell transplant recipients, advanced or untreated HIV, primary immunodeficiency, patients on immunosuppressive medications (high-dose corticosteroids, biologics, B-cell depleting agents)
Monitoring: Some centers perform post-vaccination antibody testing to assess response, though this is not universally recommended
Missed Dose
If a dose is missed or delayed, it should be given as soon as possible without restarting the series. There is no need to begin the schedule over. Longer intervals between doses do not reduce final immunity and may actually enhance the antibody response.
Overdose
Overdose with Spikevax XBB.1.5 is extremely unlikely because doses are prepared in single-dose vials or pre-measured syringes. In rare reports of inadvertent administration of higher-than-intended doses, symptoms have generally been similar to those seen after standard doses but of greater intensity (more severe injection-site pain, fatigue, headache, fever). Management is supportive and may include paracetamol and rest. If you believe you have received an incorrect dose, inform your healthcare provider.
How Spikevax XBB.1.5 Is Given
Spikevax XBB.1.5 is supplied as a white to off-white dispersion for injection in multi-dose vials. The vial must be inspected for particulate matter and discoloration before use. The dispersion should be gently swirled before each withdrawal — it must not be shaken. Depending on the supplied formulation, the vaccine is either ready to use or requires no dilution.
Once a dose is drawn into the syringe, it should be injected promptly. After administration, the vaccination record should be documented with the product name, lot number, date, site of administration, and the administering clinician. The recipient is asked to wait 15 minutes (or 30 minutes if they have a history of anaphylaxis or immediate allergic reactions) in the clinic to allow prompt management of any acute allergic reaction.
Spikevax XBB.1.5 is always prepared and administered by trained healthcare professionals in vaccination centers, pharmacies, primary care practices, hospitals, schools, or workplaces with appropriate authorization. You cannot purchase or self-administer this vaccine at home. Emergency equipment and personnel able to manage anaphylaxis must be available at the site of vaccination.
What Are the Side Effects of Spikevax XBB.1.5?
Like all vaccines, Spikevax XBB.1.5 can cause side effects, but not everyone will experience them. Side effects generally reflect the immune system responding to the vaccine, which is a sign of the intended biological action. Most reactions appear within 1 to 2 days after vaccination and resolve spontaneously within 1 to 3 days. Simple measures such as paracetamol or ibuprofen for pain, applying a cool compress to the injection site, and drinking fluids are usually sufficient to manage symptoms.
Immediate Reactions
Immediate reactions, including allergic responses, can occur during the 15 to 30 minutes following injection. These include local injection-site reactions and, very rarely, systemic allergic reactions (anaphylaxis). All vaccination sites are equipped to manage acute reactions, including epinephrine (adrenaline), antihistamines, and resuscitation equipment.
Side Effects by Frequency
Very Common
May affect more than 1 in 10 people
- Pain, tenderness, or swelling at the injection site
- Redness at the injection site
- Swollen or tender lymph nodes under the arm or in the neck (lymphadenopathy)
- Headache
- Fatigue or tiredness
- Muscle pain (myalgia)
- Joint pain (arthralgia)
- Chills
- Fever (temperature ≥38°C)
- Nausea or vomiting
- General feeling of being unwell (malaise)
Common
May affect up to 1 in 10 people
- Rash at or around the injection site (including delayed “COVID arm” reaction appearing 7–10 days after vaccination)
- Hives or widespread rash
- Diarrhea
- Abdominal pain
- Dizziness
- Itching at the injection site
- Raised arm temperature or warmth
- Decreased appetite (more often reported in children)
- Irritability or crying (in young children)
- Drowsiness
Uncommon
May affect up to 1 in 100 people
- Facial swelling (particularly in individuals who have had dermal fillers)
- Dermatitis
- Tinnitus (ringing in the ears)
- Delayed large local reactions appearing days after injection
Rare
May affect up to 1 in 1,000 people
- Bell’s palsy (temporary one-sided facial weakness)
- Acute peripheral facial paralysis
- Extensive swelling of the vaccinated limb
Very Rare / Not Known
Fewer than 1 in 10,000 or frequency cannot be estimated
- Myocarditis (inflammation of the heart muscle)
- Pericarditis (inflammation of the lining around the heart)
- Anaphylaxis (severe allergic reaction)
- Erythema multiforme
- Capillary leak syndrome (in individuals with prior history)
- Paresthesia (abnormal skin sensations)
- Heavy menstrual bleeding (typically transient)
Myocarditis and Pericarditis — What to Watch For
Myocarditis and pericarditis following mRNA COVID-19 vaccination have been identified as rare but important adverse events. Most reported cases have occurred in males aged 12 to 29, typically within 7 days after the second dose of a primary series. Signs and symptoms include:
- New chest pain, pressure, or discomfort
- Shortness of breath on exertion or at rest
- Palpitations or awareness of heartbeat
- Feeling faint or light-headed
If any of these symptoms develop in the days to weeks after vaccination, seek medical attention promptly. Most reported cases have responded well to standard treatment with anti-inflammatory medications, and the majority of patients recover fully. Despite this risk, the benefit-risk balance for mRNA COVID-19 vaccines remains strongly favorable, as COVID-19 itself causes myocarditis more commonly and severely than vaccination does.
Reactogenicity in Different Groups
In general, younger adults and adolescents report more frequent and intense reactogenicity (fever, fatigue, muscle aches) than older adults. This reflects a more vigorous immune response, not a safety concern. Children aged 6 months to 5 years typically have milder reactions than older children and adolescents. Immunocompromised individuals may have less intense local and systemic reactions, consistent with a reduced immune response.
Seek urgent medical attention if you experience: difficulty breathing, swelling of the face or throat, fast heartbeat, dizziness or fainting, severe rash all over the body, new or worsening chest pain, persistent high fever beyond 48 hours, or any symptom that concerns you. Routine mild reactions can typically be managed with rest, fluids, paracetamol, or ibuprofen.
If you experience any side effects, including those not listed here, tell your doctor or nurse. You can also report suspected side effects to your national pharmacovigilance authority (e.g., the EMA EudraVigilance system in Europe, the FDA Vaccine Adverse Event Reporting System (VAERS) in the United States, or the MHRA Yellow Card Scheme in the United Kingdom) to help monitor the ongoing benefit-risk profile of Spikevax XBB.1.5.
How Should Spikevax XBB.1.5 Be Stored?
Keep this medicine out of the sight and reach of children. Do not use after the expiry date stated on the vial label and outer carton. The expiry date refers to the last day of that month.
- Long-term storage (unopened vials): Frozen at −50°C to −15°C in the original carton to protect from light. Shelf life when frozen: up to the expiry date printed on the package.
- Short-term refrigerated storage (thawed, unopened vials): 2°C to 8°C, up to 30 days. Vials can be moved between refrigerated and room-temperature storage within specified limits.
- Room-temperature storage (thawed, unopened vials): 8°C to 25°C for up to 24 hours total, including time for transport and preparation.
- After first puncture (in-use stability): Each multi-dose vial must be used within 12 hours when stored at 2°C to 25°C after the first needle insertion.
- Do not refreeze: Once thawed, the vaccine must never be refrozen. Do not use if the product has been frozen a second time.
- Inspection: Do not use if you observe particles, discoloration, or a compromised vial integrity.
Storage and cold-chain logistics for Spikevax XBB.1.5 are managed entirely by the manufacturer’s distribution network, national vaccination programs, and the healthcare facility where the vaccine is administered. Individual recipients never need to store the vaccine themselves. The strict cold-chain requirements reflect the inherent instability of the mRNA and lipid nanoparticle components; these controls ensure that every dose administered retains its full potency.
Do not dispose of any medicines via wastewater or household waste. Unused vaccine and all materials used for administration (syringes, needles, vials) are considered biohazard medical waste and are disposed of according to local regulations by the healthcare facility.
What Does Spikevax XBB.1.5 Contain?
Active Substance
The active substance in Spikevax XBB.1.5 is elasomeran, a single-stranded, 5’-capped, nucleoside-modified messenger RNA (modRNA) that encodes the full-length spike (S) glycoprotein of the SARS-CoV-2 Omicron XBB.1.5 subvariant. The mRNA contains two proline substitutions in the S2 subunit (“2P” stabilization) that lock the spike protein in its prefusion conformation, optimizing its recognition by the immune system. Nucleoside modifications (notably replacement of uridine with N1-methylpseudouridine) reduce innate immune detection of the mRNA itself while improving translation efficiency.
Each 0.5 mL adult dose contains 50 micrograms (μg) of elasomeran. The pediatric dose (6 months to 11 years) is 25 μg in 0.25 mL. The mRNA is formulated in lipid nanoparticles (LNPs) that protect it from degradation in blood and extracellular fluid and enable delivery into host cells after injection.
Lipid Nanoparticle Components
The lipid nanoparticles consist of four lipids that self-assemble around the mRNA:
- SM-102 — a proprietary ionizable cationic lipid that facilitates mRNA delivery into cells
- Cholesterol — provides structural stability
- DSPC (1,2-distearoyl-sn-glycero-3-phosphocholine) — a helper phospholipid
- PEG2000-DMG (1,2-dimyristoyl-rac-glycero-3-methoxypolyethylene glycol-2000) — a polyethylene glycol-conjugated lipid that prevents particle aggregation and extends circulation time
Inactive Ingredients (Excipients)
- Trometamol (tromethamine)
- Trometamol hydrochloride
- Acetic acid
- Sodium acetate trihydrate
- Sucrose
- Water for injections
Spikevax XBB.1.5 contains no preservatives (such as thiomersal or mercury-containing compounds), no adjuvants (such as aluminum salts), no eggs or egg proteins, no gelatin, no latex, and no antibiotics. The vaccine is manufactured using a cell-free, enzymatic process; no animal- or human-derived cell lines are used in production, and the product does not contain live or inactivated virus.
Appearance
Spikevax XBB.1.5 is a white to off-white dispersion that may contain white or translucent product-related particulates. After thawing, the solution should be visually inspected: do not use if it is discolored or contains foreign particulate matter. The multi-dose vial has a lavender or similar color-coded cap and label, depending on region, to help distinguish it from earlier vaccine formulations.
Packaging
Spikevax XBB.1.5 is supplied in multi-dose vials containing either 10 doses of 0.5 mL each (5 mL total) or variable-volume formats. Pack sizes and label presentations may vary by country and by healthcare system distribution practices. Each carton typically contains 10 multi-dose vials.
Manufacturer
Spikevax XBB.1.5 is manufactured and marketed by Moderna Biotech (headquarters in Cambridge, Massachusetts, United States) and Moderna Biotech Spain S.L. for distribution in the European Union. The marketing authorization holder for the European Economic Area is Moderna Biotech Spain S.L., Madrid, Spain. Manufacturing sites are located in multiple countries including the United States, Spain, and Switzerland.
Frequently Asked Questions About Spikevax XBB.1.5
Spikevax XBB.1.5 is a variant-adapted mRNA vaccine used for active immunization against SARS-CoV-2 infection and severe COVID-19 in adults, adolescents, and children aged 6 months and older. It is indicated for primary vaccination in those never previously vaccinated and, more commonly, as a booster dose in those with prior vaccination or infection. The vaccine is specifically adapted to the Omicron XBB.1.5 subvariant but also induces cross-reactive immunity against related circulating variants.
Immunogenicity studies have shown that Spikevax XBB.1.5 generates high levels of neutralizing antibodies against the XBB.1.5 subvariant and cross-reactive antibodies against related Omicron lineages, including BA.2.86 and JN.1. Real-world effectiveness studies have found that updated XBB.1.5-adapted vaccines reduce the risk of symptomatic COVID-19 by approximately 40–60% and the risk of hospitalization by 60–80% during the first months after vaccination. Effectiveness is particularly high against severe outcomes, although protection against mild symptomatic infection wanes over several months.
Myocarditis (inflammation of the heart muscle) is a rare but recognized adverse event after mRNA COVID-19 vaccines. It is most commonly reported in adolescent and young adult males, typically within 7 days after the second dose of a primary series. The overall reported rate is fewer than 1 in 10,000 vaccinations. Most reported cases have been mild, responded to standard anti-inflammatory treatment, and resolved without long-term consequences. COVID-19 infection itself causes myocarditis more frequently and more severely than the vaccine does. Seek medical attention immediately if you experience chest pain, shortness of breath, or palpitations after vaccination.
Yes. Large real-world studies involving hundreds of thousands of vaccinated pregnant individuals have shown that mRNA COVID-19 vaccines, including Spikevax, are safe during pregnancy and do not increase the risk of miscarriage, stillbirth, preterm birth, or birth defects. In contrast, COVID-19 during pregnancy is associated with elevated maternal and neonatal risks. International guidelines from the WHO, CDC, RCOG, ACOG, and FIGO recommend COVID-19 vaccination during pregnancy. Breastfeeding is also compatible with vaccination; vaccine-induced antibodies pass into breast milk and may offer additional passive protection to the infant.
Yes. Spikevax XBB.1.5 can be safely co-administered with seasonal influenza vaccines and most other routine vaccines, including pneumococcal and recombinant zoster vaccines. Co-administration may result in a modest increase in reactogenicity (fatigue, headache, muscle aches) for 1 to 2 days but does not reduce the effectiveness of either vaccine. If you prefer, vaccines can be given on separate visits or into different arms to help identify any reaction. Consult your healthcare provider for personalized scheduling.
Spikevax XBB.1.5 should not be given to anyone with a documented severe allergic reaction (anaphylaxis) to a previous dose of an mRNA COVID-19 vaccine or to any vaccine component, including polyethylene glycol (PEG) or trometamol. People who developed myocarditis or pericarditis after a previous mRNA vaccine dose should discuss further vaccination with a cardiologist or immunization specialist. Individuals with bleeding disorders or on anticoagulants can be vaccinated with additional precautions. Most other medical conditions, including allergies to foods or other medications, are not contraindications.
References
- European Medicines Agency (EMA). Spikevax (elasomeran) – Summary of Product Characteristics. Last updated 2025. Available from: EMA EPAR.
- U.S. Food and Drug Administration (FDA). Spikevax (COVID-19 Vaccine, mRNA) Prescribing Information. Revised 2025. Available from: FDA Spikevax Information.
- World Health Organization (WHO). Statement on the antigen composition of COVID-19 vaccines – Technical Advisory Group on COVID-19 Vaccine Composition (TAG-CO-VAC). Geneva: WHO; 2024.
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