The U.S. Food and Drug Administration (FDA) has issued an Emergency Use Authorization (EUA) for Moderna's COVID-19 vaccine, as expected after an independent panel commissioned by the administration recommended its approval earlier this week. This is the second vaccine now authorized for use in the U.S. under EUA, after the Pfizer -BioNTech vaccine was approved last week.
Moderna's vaccine could begin being administered to Americans by "Monday or Tuesday" next week, according to Dr. Anthony Fauci speaking to NBC's Today show in a new interview. That's in keeping with the timelines between the Pfizer EUA and the first patients actually receiving the vaccine last week.
Like Pfizer's vaccine, Moderna's is an mRNA therapy. That means that it contains no actual virus -- just genetic instructions that tell a person's body to create a specific protein. That protein is more or less identical to the one that SARS-CoV-2, the virus which causes COVID-19, uses to attach to a host's cells and replicate. Moderna's vaccine causes a person to create just the protein, which on its own is harmless, and then their natural defenses via their immune system react to that and develop a method for fighting it off. That defense system is "remembered" by the body, while the vaccine itself naturally dissolves after a brief time, leaving a person with immunity but nothing else.
The Oxford-AstraZeneca vaccine, which has yet to be approved for use in the U.S., uses a weakened and modified common cold virus that doesn't spread in humans to create the spike protein in recipients, resulting in the body generating its own immune response. That's a much more tried-and-tested method for creating a vaccine, but both Moderna and Pfizer's mRNA therapies have shown to be very effective in preliminary data from their large Phase 3 clinical trials.