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The Pfizer-BioNTech COVID-19 Vaccine (Comirnaty) and the Moderna COVID-19 vaccines (Spikevax, mNexspike) are lipid nanoparticle-formulated, nucleoside-modified mRNA vaccines encoding the prefusion spike glycoprotein of SARS-CoV-2, the virus that causes COVID-19. The 2026–2027 mRNA vaccines target the Omicron JN.1-lineage XFG strain. Moderna’s mNexspike was first licensed in 2025 for ages 12 years and older. It is designed to reduce the amount of mRNA required to elicit the same or slightly better immune response compared to Spikevax (10 mcg of mRNA versus 50 mcg of mRNA for an adult dose). CDC states that Spikevax and mNexspike may be used interchangeably when both are age appropriate. Visit the Children’s Hospital of Philadelphia (CHOP) Vaccine Education Center website for more details, including short videos, about how mRNA vaccines work: www.chop.edu/vaccine-education-center/science-history/vaccine-science/how-are-vaccines-made#mrnavaccines.