CNBC's Anne Rimoin, an epidemiologist, said she agreed with Dr. Anthony Fauci, White House chief medical advisor. He stated that everyone will one day "likely" require a booster shot of Covid-19 vaccines.Rimoin, an epidemiologist at the UCLA School of Public Health, said, "Well, Dr. Fauci is correct."A booster shot will be necessary if we begin to see a decline in the effectiveness of the vaccine in preventing severe diseases and hospitalizations or death. Although we're not yet there, we will need to get there.After a critical panel unanimously approved third doses for Americans with immunocompromised diseases, the Centers for Disease Control and Prevention granted final approval Friday to begin administering Covid-19 booster shot to Moderna and Pfizer vaccine recipients. Following approval by the Food and Drug Administration late Thursday night of booster shots for immunocompromised people, the CDC made the final decision.Rimoin stated to CNBC's "The News With Shepard Smith” that both agencies made an "important" decision regarding the immunocompromised population.Rimoin stated that even though they received the vaccine, their immune system was not strong enough to protect them against the virus. "That is why both the FDA (and the CDC) are recommending that these individuals get an additional dose. Studies have shown that it can improve immunity in around 1/3 to 1/2 the population.The U.S. has 2.7% of its adult population, and 44% of its hospitalized breakthrough infection patients. This is where an individual can get infected even though they have been fully vaccinated.