This animated video explains how Pfizer’s genetic vaccine works against COVID-19.

Pfizer announced Monday that its vaccine may be 90% effective, based on early and incomplete test results. The Food and Drug Administration must still authorize its use, and the Centers for Disease Control and Prevention is in charge of deciding who is first in line for the extremely limited supplies that will first come out.

This situation is constantly changing, but as of now it looks like the earliest vaccine makers will be able to ask for emergency authorization from the FDA is the third week of November, and then it will be some time – maybe several weeks – before the agency allows it. Vaccines will then be available only to a small group of people.

The CDC is in charge of deciding who is first in line for the extremely limited supplies that will available initially, and the states have to follow CDC’s decision. And while vague outlines of prioritization are emerging, the final decision will be customized to each vaccine and announced only when each gets FDA clearance.

If the Pfizer vaccine is approved, Williams said it would be distributed in Missouri from Pfizer’s Chesterfield facility in suburban St. Louis to five regional centers. Williams warned it could be late April or early May before a vaccine is available to everyone who wants it.