How do vaccine ingredient lists compare between original COVID-19 mRNA vaccines (2020–2021) and updated bivalent or variant-specific formulations (2022–2024)?
Original mRNA COVID-19 vaccines (Pfizer-BioNTech, Moderna) introduced in late 2020 used lipid nanoparticle-formulated mRNA and a short list of excipients; later updates from 2022–2024 shifted only the...