On September 23, the Centers for Disease Control and Prevention (CDC) officially recommended a booster shot for Pfizer COVID-19 vaccine series recipients age 65 and older, those between 18 and 64 who are at high risk for severe COVID-19 due to underlying conditions, and those 18-64 with frequent institutional or occupational exposure to the virus. This announcement followed a previous approval of a third dose for immunocompromised individuals who had received either the Moderna or Pfizer COVID-19 vaccine.
So, what exactly is a third dose/booster, and how does it work? Janette Nesheiwat, MD, Medical Director at CityMD, and Eleanora Yeiser, DO, a Summit Health family medicine doctor, answer these and other pressing COVID-19 booster shot questions.
The COVID-19 booster (whether Pfizer or Moderna) shot is exactly the same shot that was given for dose one and dose two. Simply put, "The booster has the same ingredients and works the same way as the first two doses," says Dr. Nesheiwat. “It's similar to other vaccines that require at least two or three doses such as hepatitis B, MMR, and tetanus.”
This does not mean the initial vaccines didn't work. Protection from the original dose naturally decreases over time. “The booster is an additional layer of protection provided at a later time,” Dr. Yeiser says. “It helps boost the immune system’s recognition of the virus,” she adds.
Even with clear guidelines set forth by the CDC, there are many unreliable sources spreading vaccine misinformation and causing confusion over eligibility. At this time, immunocompromised individuals who received the Moderna or Pfizer COVID-19 vaccine series are eligible to receive a third dose to improve protection from infection. These patients should get their third dose 28 days (or later) after their second dose.
Additionally, for those who received the Pfizer/BioNTech COVID-19 vaccine, a booster is recommended 6 months after the second dose if you are 65 and older or at high risk of contracting severe COVID-19 due to underlying medical conditions or due to exposure risk. This includes teachers and grocery store workers. A complete list can be found on the CDC’s website.
If you are eligible based on the criteria set forth by the CDC, you should consider getting the booster. While extensive evidence has shown that all the vaccines—Pfizer, Moderna, and Johnson & Johnson/Janssen— are highly effective in preventing severe disease, even without a booster, antibody levels from vaccination typically do decline over time. Studies show that this waning likely occurs at around the 6-8 month mark, but Dr. Nesheiwat cautions, "This may change as the data that guides our clinical recommendations evolves.”
Dr. Yeiser agrees, emphasizing, "If you had the second Pfizer shot more than six months ago and you are over 65 or at higher risk, I’d recommend getting the booster. But for all others, patience is needed as new information is gathered weekly from research.”
"Data collection regarding safety and efficacy of mixing vaccine brands is limited," says Dr. Yeiser says. "It's best to complete vaccine series and boosters with the same brand, as the CDC advises."
Dr. Nesheiwat concurs, noting that both the FDA and CDC recommend not doing so until they know more about the effects of mixing and matching vaccinations.
Vaccines should only be mixed when there is limited availability and delaying the dose could place someone at increased risk.
There are several COVID-19 vaccination location options people can consider, including state and local vaccine sites and retail pharmacies.
To learn more about current booster eligibility, read our article, FDA Approves the Pfizer/BioNTech Booster for COVID-19 Vaccine: 10 Things to Know.
COVID-19 vaccine information is constantly evolving. Please be sure to check the CDC’s website for the most up-to-date information.