The Centers for Disease Control and Prevention's Advisory Committee on Immunization Practices convened on Wednesday (September 22) for the first day of a two-day meeting to discuss whether to recommend a third booster shot for Pfizer's COVID-19 vaccine.

Ruth Link-Gelles, who leads the CDC's Vaccine Effectiveness Team, said that she has reviewed multiple studies about the long-term effectiveness of the COVID vaccines and found that the efficacy does wane over time, especially in older Americans.

"For individuals 65 plus, we saw significant declines in VE (vaccine effectiveness) against infection during Delta for the mRNA products," Link-Gelles said during the meeting.

"We also saw declines, particularly for Pfizer, for 65 up, that we're not seeing in younger populations. Finally, there's evidence of waning VE against hospitalization in the Delta period," she added.

Natalie Thornburg, a CDC scientist, told the panel that a decreasing number of antibodies does not necessarily mean that people aren't protected against COVID-19.

"Antibodies decrease over time as we expected, in all age groups, but cellular memory is maintained," she said.

Dr. Sarah Long, a pediatric infectious disease expert at Drexel University College of Medicine, added that researchers must determine the minimum number of antibodies needed to provide protection so they can accurately determine who needs a booster.

The committee stressed that the priority should be getting as many people vaccinated as possible because that is the best way to prevent unnecessary deaths from COVID-19.

"I want to highlight that in September of 2021 in the United States, deaths from COVID-19 are largely vaccine-preventable with the primary series of any of the three vaccines available," Dr. Matthew Daley, a researcher at Kaiser Permanente Colorado, said.

The panel is expected to vote on their decision whether to recommend booster shots on Thursday.

The meeting comes after the Food and Drug Administration's Vaccines, and Related Biological Products Advisory Committee voted against recommending a third booster shot of Pfizer's COVID-19 vaccine for people over the age of 16. The panel did vote in favor of recommending a booster shot for those over the age of 65 and those who have a high risk of severe COVID complications.

The FDA has not made any decisions based on the recommendations of the panel.