RSV vaccines currently require reconstitution before administration, and the steps differ depending on the brand. Both Arexvy (GSK) and Abrysvo (Pfizer) come as a powder that must be mixed with a liquid component to produce a 0.5 mL injectable dose. The process takes only a few minutes, but the mixing technique, storage rules, and visual checks vary between products.
Reconstituting Arexvy (GSK)
Arexvy arrives as two separate vials: one containing a white powder (the lyophilized antigen) and one containing the adjuvant suspension, an opalescent liquid that ranges from colorless to pale brownish. Both vials should be stored refrigerated at 2°C to 8°C (36°F to 46°F) until you’re ready to prepare the dose.
Start by cleansing both vial stoppers. Using a sterile needle and sterile syringe, withdraw the entire contents of the adjuvant suspension vial (the liquid), tilting the vial slightly to capture the full volume. Then slowly transfer the entire contents of the syringe into the antigen vial (the powder). Gently swirl the vial until the powder is completely dissolved. Do not shake vigorously, as this can damage the protein components in the vaccine.
Once mixed, the solution should appear opalescent and colorless to pale brownish. Inspect it for particles or unusual discoloration. If either is present, discard the vial. When the solution looks correct, withdraw 0.5 mL from the reconstituted vial and administer it intramuscularly.
Reconstituting Abrysvo (Pfizer)
Abrysvo uses a different setup. It comes with a vial of white lyophilized powder, a prefilled syringe of sterile water diluent, and a needle-free vial adapter. Both the powder and diluent should be stored refrigerated at 2°C to 8°C (36°F to 46°F) before preparation.
The process has five steps:
- Attach the vial adapter. Peel off the top cover of the adapter packaging but leave the adapter inside. Align the adapter spike over the center of the vial’s rubber stopper and push straight down to lock it into place. Do not push at an angle.
- Connect the syringe. Remove the cap from the prefilled syringe while holding the Luer lock adapter. Connect the syringe to the vial adapter by turning clockwise. Do not overtighten.
- Inject the diluent and swirl. Push the plunger to inject all the sterile water into the vial. Keep the empty syringe attached. While holding the plunger down, gently swirl the vial until the powder fully dissolves. Do not shake.
- Withdraw the dose. Slowly pull back the plunger to withdraw the entire contents of the vial into the syringe, yielding approximately 0.5 mL.
- Disconnect and attach a needle. Hold the Luer lock adapter and turn the syringe counterclockwise to disconnect it from the vial adapter. Attach a sterile needle suitable for intramuscular injection.
The reconstituted Abrysvo solution should be clear and colorless. Inspect it before injection and discard if you see particles or discoloration.
Why Gentle Swirling Matters
Both vaccines contain proteins that are sensitive to physical stress. Vigorous shaking can cause the proteins to denature or aggregate, forming visible particles and potentially reducing the vaccine’s effectiveness. Gentle swirling dissolves the powder while keeping the protein structure intact. If the powder doesn’t dissolve completely after swirling for a reasonable time, do not attempt to force it by shaking harder.
Storage After Reconstitution
The two vaccines have different post-mixing storage rules, and confusing them can result in a wasted dose.
Reconstituted Arexvy can be stored either refrigerated at 2°C to 8°C (36°F to 46°F) or at room temperature up to 25°C (77°F). Ideally, administer it as soon as possible after mixing.
Reconstituted Abrysvo must be stored only at room temperature, between 15°C and 30°C (59°F to 86°F), and used within 4 hours. Do not refrigerate or freeze the reconstituted Abrysvo solution. Refrigerating it after mixing goes against the manufacturer’s instructions and is grounds for discarding the dose.
Dose and Administration Route
Both Arexvy and Abrysvo are given as a single 0.5 mL intramuscular injection. The preferred injection site is the deltoid muscle of the upper arm. The outer thigh (vastus lateralis) is an acceptable alternative. These are one-time vaccines for older adults, not annual shots like the flu vaccine. Abrysvo is also approved for pregnant individuals at 32 to 36 weeks gestational age as a single 0.5 mL dose.
For the injection itself, a 22 to 25 gauge needle is standard for intramuscular vaccination in adults. Use a separate sterile needle and syringe for the reconstitution steps if the product requires it (as with Arexvy), and a fresh sterile needle for the actual injection.
Common Preparation Errors to Avoid
The most frequent mistakes during RSV vaccine reconstitution are straightforward to prevent once you know what to watch for. Never use a diluent from a different product. Arexvy’s adjuvant suspension is specific to that vaccine, and Abrysvo’s sterile water syringe is designed for its formulation. Swapping diluents between brands, or substituting generic sterile water for injection, will produce an incorrectly formulated dose.
With Abrysvo’s vial adapter, angling the spike during attachment can crack the stopper or create a poor seal. Push straight down. Also, keep the syringe connected to the adapter during swirling so the system stays closed and sterile.
Finally, always check the expiration dates on both components before reconstitution. The powder and the liquid may have different expiration dates, and the earlier date governs whether the vaccine is still usable.