After Pfizer and BioNTech received an Emergency Use Authorization (EUA) from the Food and Drug Administration (FDA) for their COVID-19 vaccine on Dec. 11, vaccinations have begun in all 50 states. Front-line workers and the elderly have been prioritized to receive the vaccine first.

In California, seven locations received the first shipments of the Pfizer vaccine, including the University of California, San Francisco (UCSF) and Zuckerberg San Francisco General. As of Jan. 6, 486,087 people in California have received their first dose of either the Pfizer or Moderna vaccine.

Part 1: Storage

Pfizer’s vaccine is transported in thermal shippers which use dry ice to maintain an internal temperature of -70˚C, providing storage for up to 30 days. The vaccine is then transferred to refrigerators at 2-8°C for up to five days and must be diluted in a saline solution before being used within six hours.

Part 2: Efficacy

The vaccine’s high effectiveness comes from its use of messenger RNA (mRNA), which sends instructions to human cells for the production of spike proteins. These proteins, found on the surface of the virus, stimulate the immune system to produce antibodies and prepare it for a severe infection.

Part 3: Response

If infected, the body’s antibodies bind to the viruses’ surface, engulfing it and preventing its spike proteins from attaching to human cells. Immune cells can then find and destroy any potentially infected cells, which contain spike proteins on their surface.

Part 4: Dosage

In order to achieve its full efficacy, the vaccine must be administered in two doses, three weeks apart. The company expects to produce 50 million doses by the end of the year, and according to the Centers for Disease Control and Prevention, as of Jan. 6, over 5.3 million people in the U.S. have received the first dose of the vaccine.