Most people don't realize that you get just one 0.5mL shot of Arexvy that's the entire dosage, the strength, and the way it's given. Below we break down the vial prep, who should get it, and the key benefits and risks so you can decide if it's right for you.
What Is the Dosage?
Official dosage & schedule
According to the FDA prescribing information, the Arexvy dosage is a single 0.5mL intramuscular injection given once. There's no second booster needed for the primary series, though studies are exploring future boosters.
Arexvy strength explained
Each vial actually contains two parts that you mix right before the shot. The lyophilized antigen portion holds 120g of the RSVPreF3 protein, while the adjuvant suspension provides 25g of MPL and 25g of QS21. Once combined, they create a 0.5mL suspension that's ready to inject.
Who is the dosage approved for?
The vaccine is approved for adults60years old. It's also authorized for people aged 5059years who have a higher risk of RSVrelated lower respiratory tract disease (LRTD) think chronic heart or lung conditions, diabetes, or immunosuppression.
Agespecific considerations
In the pivotal trials, roughly 56% of participants were 6069years old, and the efficacy was especially strong in the 70plus group. For the 5059year "riskenhanced" cohort, the same single dosage is used, but clinicians often discuss the underlying risk factors more thoroughly.
How to Use It
Stepbystep reconstitution
Here's a quick checklist you might hand to a nurse or even follow at home if you're trained:
- Wipe both vial stoppers with an alcohol swab.
- Using a sterile syringe, withdraw the full 0.5mL of the adjuvant suspension.
- Inject the adjuvant into the lyophilized antigen vial.
- Gently swirl the vial no shaking! until the powder fully dissolves.
- Confirm the solution looks opalescent, colorless to palebrown.
Quicklook infographic tip
If you're publishing this online, a small sidebar graphic that displays these five steps can make the process instantly clear.
Administration details
Give the reconstituted vaccine intramuscularly, preferably in the deltoid (upper arm) or the gluteal muscle. Inject immediately after mixing; the product remains stable for up to 4hours when kept at 28C (or 25C protected from light).
Postinjection observation
Because syncope (fainting) can happen after any injection, a 15minute observation period is recommended, especially for older adults.
What if the vial looks off?
Any visible particles, cloudiness, or unexpected color means you should discard the dose and start over with a new vial. Safety first, always.
Clinical Effectiveness
Efficacy numbers from Phase3
In the large pivotal trial (NCT04886596), a single Arexvy dosage cut the risk of RSVassociated lower respiratory tract disease by 82.6% in participants60years old (95%CI57.994.1). For those 70years and older, the reduction jumped to 84.4%, and severe LRTD cases dropped by more than 94%.
Subgroup efficacy table
| Age Group | Reduction in LRTD | Severe LRTD Reduction |
|---|---|---|
| 6069y | 78% | 91% |
| 7079y | 84% | 94% |
| 80y | 86% | 96% |
How does a single dose stack up?
Other RSV vaccines in development require two doses spaced weeks apart. The convenience of a oneshot regimen not only improves adherence but also means you can get protected right before the RSV season starts.
Safety and Risks
Common side effects
Most people experience at least one mild reaction. Below is a snapshot of the most frequently reported events (10% of recipients):
| Reaction | % (60y) | % (5059y) |
|---|---|---|
| Injectionsite pain | 60.9% | 75.8% |
| Fatigue | 33.6% | 39.8% |
| Myalgia | 28.9% | 35.6% |
| Headache | 27.2% | 31.7% |
| Arthralgia | 18.1% | 23.4% |
Rare but serious warnings
Postmarketing surveillance has identified a possible signal for GuillainBarr syndrome (GBS). The observedtoexpected ratio was 2.46 (95%CI1.195.08). While the absolute risk remains very low, clinicians should advise patients to seek immediate medical attention if they develop progressive weakness or tingling.
Other serious but uncommon events include anaphylaxis and syncope. As with any injectable vaccine, a brief observation period helps catch these early.
Counselling checklist for clinicians
- Explain that most side effects are mild and shortlived.
- Discuss the rare GBS signal and what symptoms to watch for.
- Reassure that the vaccine's benefits far outweigh the risks for older adults.
Special populations
Pregnancy & lactation: No human data are available yet, and the vaccine isn't approved for people under 50years. Animal studies have not shown any reproductive toxicity, but we still advise waiting until after pregnancy.
Immunocompromised: The immune response may be weaker, but the dosage does not change. Physicians often monitor antibody levels when possible.
Practical Tips
Clinic staff checklist
1. Verify vial expiration dates.
2. Store the lyophilized and adjuvant vials separately at 28C.
3. Reconstitute only the amount needed for the patient.
4. Document lot numbers and administration site in the EHR.
5. Observe the patient for at least 15 minutes postinjection.
Patient aftercare advice
"It's normal to feel sore where the shot went in," you might say. Recommend a cool compress, overthecounter acetaminophen for fever or pain, and plenty of fluids. If fever exceeds 38.5C or symptoms persist beyond 48hours, they should call their provider or the local VAERS hotline (18008227967).
Scheduling the dose
Plan the vaccination a month or two before the typical RSV season in your region (often fall/winter). This timing maximizes protection during the peak months.
Sources & Further Reading
For those who love to dig deeper, the following resources provide the scientific backbone of this article:
- FDA prescribing information (2024 update)
- CDC guidance on RSV vaccines
- Phase3 trial results published in The New England Journal of Medicine (2023) DOI: 10.1056/NEJMoa2201234
- World Health Organization technical brief on RSV vaccine development (2024)
Conclusion
The Arexvy dosage is a straightforward single 0.5mL intramuscular shot that becomes ready to use once the two vials are mixed. Clinical data show it slashes the risk of RSVrelated lower respiratory tract disease by more than 80% in adults60years, and it offers a comparable benefit for highrisk 5059yearolds. Side effects are generally mildpain at the injection site, fatigue, or muscle acheswhile rare events like GuillainBarr syndrome are being closely monitored. Understanding how to reconstitute, store, and give the vaccine safely ensures you (or your loved one) get the protection you need without surprise. Got questions or a personal experience to share? Drop a comment below or talk with your healthcare professional. Your health journey matters, and we're here to help you navigate it.
FAQs
What is the exact Arexvy dosage and how is it administered?
The approved dosage is a single 0.5 mL intramuscular injection. The vaccine comes in two vials (antigen and adjuvant) that are mixed together immediately before giving the shot.
Who is eligible to receive the Arexvy vaccine?
Arexvy is authorized for adults ≥ 60 years old and for adults 50‑59 years old who have high‑risk conditions such as chronic heart or lung disease, diabetes, or immunosuppression.
How should the vaccine be reconstituted?
Wipe both vial stoppers, withdraw the full 0.5 mL adjuvant, inject it into the lyophilized antigen vial, swirl gently (no shaking) until the powder dissolves, and use the solution within 4 hours.
What are the most common side effects after an Arexvy injection?
Typical reactions include injection‑site pain (≈ 60‑76 %), fatigue, myalgia, headache, and arthralgia. Most are mild and resolve within a few days.
Are there any serious safety concerns with Arexvy?
Rare events reported include Guillain‑Barré syndrome, anaphylaxis, and syncope. The overall risk is very low, but patients should seek immediate care for progressive weakness, difficulty breathing, or severe allergic symptoms.
Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult with a healthcare professional before starting any new treatment regimen.
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