What is the difference between the original COVID-19 vaccines and the currently recommended vaccines?

The original COVID-19 vaccines all targeted the spike protein of the original SARS-CoV-2 virus. The 2024–2025 formulation vaccines target the spike proteins of more recently circulating strains, known as the Omicron KP.2 (mRNA vaccines) or JN.1 (protein vaccine) strains. The update is intended to boost production of antibodies that protect more effectively against disease caused by currently circulating Omicron subvariants.

The process of updating the strain without changing anything else is similar to the seasonal strain changes made for influenza vaccinations each year; FDA does not require manufacturers to repeat the large-scale clinical trials necessary for the original products before authorizing updated vaccines. Vaccine safety, side effects, and risk of allergic reactions are expected to be comparable to earlier formulations of vaccines of the same brand and dose. As with seasonal influenza vaccines, future COVID-19 vaccines can continue to be updated when needed, as the circulating viruses evolve.