By Sandra Rose  | 

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The Food and Drug Administration (FDA) has authorized a third coronavirus mRNA injection for "immunocompromised" people beginning on Thursday, Aug. 12.

The federal health agency expanded emergency use for Pfizer-BioNTech and Moderna mRNA to administer third "booster" shots to people with compromised or weak immunity.

The shots are authorized for people who received the first two injections and are considered immunocompromised due to cancer treatment, autoimmune disorders, HIV or other conditions that weaken the immune system.

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Americans with weak or compromised immunity are allowed to get a third coronavirus vaccine beginning on Thursday, Aug. 12.
 
ALSO READ: Should You Get a Third Vaccine Shot? The CDC Says Not Yet
 
Previously, health experts at the Centers for Disease Control (CDC) in Atlanta and the World Health Organization (WHO) said third boosters shots were not necessary.

However, Pfizer and Moderna claim third shots are needed because the first 2 injections are "wearing off" and antibody levels are decreasing among the fully vaccinated population.

Neither Pfizer nor Modern vaccines prevent the spread of the virus or prevent the fully vaccinated from contracting the virus.

Pfizer and Moderna have applied to the FDA for full approval of their vaccines.

About 50% of the U.S. population have been fully vaccinated.