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? Michael Harris, MD, internal medicine physician at Summit Health answers these and other pressing COVID-19 booster shot questions.

What Is a COVID-19 Booster Shot?

The COVID-19 booster 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.

Does This Mean the Initial Vaccines Didn’t Work?

This does not mean the initial vaccines didn’t work. Protection from the original dose naturally decreases over time. The additional dose boosts the immune system’s memory so it can continue to recognize the virus quickly and effectively. “It goes even further, with an increase in antibody response by 5- up to 20-fold, resulting in more significant immunity and effectiveness against the variants that currently exist,” says Dr. Harris. “The hope is that this will be the case with future variants as well.”

Who is Eligible? 

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 your underlying medical conditions or due to your exposure risk. This includes teachers and grocery store workers. A complete list can be found on the CDC’s website.

Should You Get a Booster?

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 this may change as the data that guides clinical recommendations evolves.

“If you had the second Pfizer shot more than 6 months ago and you are over 65 or at higher risk, get the booster. If you do not meet the criteria or had one of the other vaccines, hang tight as further recommendations will be forthcoming,” says Dr. Harris.

Can You Switch Between Authorized Vaccines?

Data collection regarding safety and efficacy of mixing vaccine brands is limited. Therefore, it’s best to complete vaccine series and boosters with the same brand, as the CDC advises. Vaccines should only be mixed when there is limited availability and delaying the dose could place someone at increased risk.

One Shot is Better Than None

If you are currently eligible but have not received the COVID-19 vaccine at all, Summit Health strongly recommends you do so. At this time, Summit Health Oregon is offering the COVID-19 booster to established primary care patients.

To learn more about current booster eligibility, visit our Coronavirus Updates page. You may also get information on vaccination sites on the Deschutes County website.

COVID-19 vaccine information is constantly evolving.

Please be sure to check the CDC’s website for the most up-to-date information.