Analysing the In-Use Stability of mRNA-LNP COVID-19 Vaccines Comirnaty™ (Pfizer) and Spikevax™ (Moderna): A Comparative Study of the Particulate Hermosilla Fernández, Jesús Alonso García, Airan Salmerón García, Antonio Cabeza Barrera, José Medina Castillo, Antonio Luis Pérez Robles, Raquel Navas Iglesias, Natalia Africa COVID-19 vaccines Comirnaty™ Spikevax™ Comirnaty™ and Spikevax™ were the first vaccines approved for human use based on modified non-replicating mRNA lipophilic nanoparticle (mRNA-LNP) technology, with great success in the treatment of COVID-19. They have been used massively worldwide. One of the major inconveniences of these vaccines is related to pharmaceutical stability issues. Proper transportation, storage, and in-use handling before administration to patients are critical steps since failures can potentially reduce potency. In this research, the in-use stability of Comirnaty™ and Spikevax™ clinical samples was analysed and the results were compared. As changes in the size of the mRNA-LNPs are related to potency, these modifications were analysed by qualitative Dynamic Light Scattering (DLS) as a stability-indicating method for control and stressed vaccine samples. Strong stress factors (accelerated light irradiation, manual shaking, and vortex vibration) and conditions that mimic in-use handling (exposure to natural light and room temperature, repeated cycles of injections, and 24 h storage in syringes) were checked. The morphology of the mRNA-LNPs was analysed by Transmission Electron Microscopy (TEM) to better interpret and support the DLS results. Although the two vaccines are based on the same mRNA-LNP technology, the results demonstrate that they are characterised by very different particle size profiles and behaviours against different handling/stress conditions. 2024-09-23T08:32:43Z 2024-09-23T08:32:43Z 2023-10-25 journal article Hermosilla, J.; Alonso-García, A.; Salmerón-García, A.; Cabeza-Barrera, J.; Medina-Castillo, A.L.; Pérez-Robles, R.; Navas, N. Analysing the In-Use Stability of mRNA-LNP COVID-19 Vaccines Comirnaty™ (Pfizer) and Spikevax™ (Moderna): A Comparative Study of the Particulate. Vaccines 2023, 11, 1635. https://doi.org/10.3390/vaccines11111635 https://hdl.handle.net/10481/94851 10.3390/vaccines11111635 eng http://creativecommons.org/licenses/by/4.0/ open access Atribución 4.0 Internacional MDPI