CDC, FDA Discuss the Effectiveness of COVID-19 Boosters


A town hall meeting with representatives from the agencies emphasized the effectiveness and likelihood of getting a third dose of the vaccine.

As the COVID-19 conversation shifts, booster shots have moved to the forefront of the conversation.

“There is some very good data to suggest that particularly in the oldest part of the population but running down through into younger individual over time the various vaccines are no longer protecting us against getting COVID-19 the same way they once did,” Peter Marks, MD, PhD, director of the Center for Biologics Evaluation and Research for the FDA, said during a town hall meeting.

Booster shots restore the immunity to what it was previously and what is being used as a “booster” is a third dose in the series of primary doses, he said.

Many adult vaccines, with the possible inclusion of the different versions of the COVID-19 vaccines, tend to follow the same trend of an initial dose, a second dose around the 1-month mark, and a third dose after 6 months, Marks said.

A third dose, or a booster dose, for the COVID-19 vaccines, would not be unheard of.

“The reason why the pandemic occurred is because there was no natural immunity. Nobody was spared this, and to develop that natural immunity, it sometimes takes a couple of doses of tickling your immune system,” Marks said.

It takes the immune system a few times to see bacteria or a virus before it can remember the infection, he said.

With variants of COVID-19 mutating, it becomes even more important to consider a third shot to boost immunity to protect against changing variants.

“The more it replicates, the more chance we have there will be an escape variant that will escape our current vaccines…the more this virus replicates, the more this chance exists,” Marks said. “The variants are going to be here with us until we get this better under control.”

The vaccine only reduces spread by about 60% to 70%, and there is evidence that supports when a population is sufficiently vaccinated that the spread becomes reduced even further, he said.

A booster shot of the Pfizer vaccine has been heavily recommend 6 months after the first dose for those who are aged 65 years and older, those aged 50 to 64 years with underlying medical conditions, and residents in long-term-care settings.

“There is also emerging evidence the shows among health care workers and other frontline workers that vaccine effectiveness against COVID-19 infections is decreasing over time,” Melinda Wharton, MD, associate director for vaccine policy for the National Center for Immunization and Respiratory Disease at the CDC, said during the town hall meeting. “This lower effectiveness is likely due to the combination of decreasing protection as time passes since getting vaccinated, that is waning immunity, as well as the greater infectiousness of the Delta variant.”

The eligibility for a booster shot extends to other groups based on the individual’s benefit and risk, which includes individuals who are aged 18 to 49 years with underlying medical conditions and those in high-risk institutional and occupational settings.

Marks noted that the adverse effects (AEs) of a third dose have been similar to the range of effects as the second dose.

He also mentioned that the most common AEs, fatigue and swollen lymph nodes, might be felt most for a few days after vaccination.

Those at the town hall meeting did not comment about booster shots for those under aged 18 years.

On October 14 and 15, 2021, the FDA will hold an advisory committee meeting about the inclusion of a booster shot for both the Janssen and Moderna vaccines.

The goal is to have a “harmonized approach to boosters for the 3 different vaccines,” Marks said.

Updated: October 8, 2021 at 10:00 am ET

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