What is the difference between 3rd doses of the COVID-19 vaccine and booster shots?

While sounding similar, there are significant differences, with third doses being approved for some, while booster shots are not — yet.

Gary Anderson, 80, was the first person to get a third dose of the COVID-19 vaccine in Routt County, when nurse Katie Cole at UCHealth Yampa Valley Medical Center gave him the shot at the end of August.
UCHealth Yampa Valley Medical Center/Courtesy photo

Gary Anderson has had every medical ailment you can name, so when he first heard he might be eligible to get his third dose of the COVID-19 vaccine, he joked he would be first in line.

“I went over to the hospital, and I said, ‘Do I qualify?'” Anderson said. “I told them what I had. … They said, ‘Sit down, you get the shot.'”

Turns out, Anderson, 80, was the first person in Routt County to get his third dose of the vaccine, and he hopes other people with a compromised immune system will roll up their sleeves as well.

Anderson, who lives in the Old Town area of Steamboat, said there are a few residents in his building that are not vaccinated, and he doesn’t understand why. He said they have told him they do not want to live their lives in fear, but Anderson said he’s actually afraid of them.

“I don’t want to get it from them,” Anderson said, adding that being vaccinated has made him feel more comfortable interacting with people if they are vaccinated. “We go out and have family get-togethers if the family has been vaccinated. We got one part of my family that hasn’t, so we don’t go there.”

Anderson was able to get his third dose of the vaccine after the Centers for Disease Control and Prevention approved the additional shot last month for people who are moderately to severely immunocompromised, which is about 3% of the population.

What Anderson did not get is a COVID-19 booster shot, which has not yet been approved for anyone.

The similarity and occasional interchanged uses of these terms has caused confusion for people wanting to have the best protection from the virus and headaches for providers turning away patients who are frustrated when they are unable to get a booster shot.

“The messaging has been complex, but the (CDC’s Advisory Committee on Immunization Practices) has been pretty clear that it’s just the immunocompromised group,” said Routt County Health Educator Jesse Herrgott.

A key Food and Drug Administration advisory panel voted Friday to recommend Pfizer-made booster shots for those 65 or older or those at high risk for the virus. But that same panel overwhelmingly voted against approving boosters for everyone, something The White House had previously announced would start to roll out Sept. 20.

The FDA usually takes that panel’s recommendation but does not have to and is expected to make a recommendation about booster shots later this week.

“Third doses imply that, for whatever reason, you didn’t have a full response to the (vaccine) series,” said Dr. Michelle Barron, senior medical director of infection prevention and control for UCHealth. “A booster implies that you did fine, you got a full response from it, but it’s because of time or for whatever reason, you need your immune system to be reminded about it.”

Essentially, a third dose is given to ensure someone with a weakened immune system gets the same protection two doses offer in most people and will only be needed by a small fraction of the population. Boosters will be more widespread, and even though the FDA panel said “no” to booster shots for everyone right now, Barron said that “no” is not forever.

“Because they said not now doesn’t mean not ever,” Barron said.

While boosters are not approved at this point, this means a small population of people with compromised immune systems will likely end up having four doses of the vaccine, Barron said, though the booster shot is not necessarily the same dose as the initial shots.

For example, someone getting a third dose of the Moderna vaccine would get 100 micrograms. By comparison, Moderna has proposed to the FDA that a booster shot is just half the amount of vaccine.

Those eligible will need to wait at least six months after their last dose of the vaccine before getting a booster shot, once approved. Barron likened trying to get a booster earlier than that to changing the oil in a car before recommended in the manual.

“Is it going to hurt your car? Probably not, but you’re sort of wasting the effort by doing it sooner,” Barron said.

The FDA is expected to authorize Pfizer’s booster, and the CDC’s Vaccine Advisory Committee will meet Wednesday and Thursday to form that agency’s recommendations about booster shots.

Moderna and Pfizer are at different points in getting a booster shot approved, and the FDA is expected to decide on the Pfizer vaccine this week. Still, Moderna and Johnson and Johnson, maker of the one-dose COVID-19 vaccine, are expected to soon present data about booster shots for people who received their vaccine.

When it comes to third doses, Barron said current guidance is to get the same vaccine previously received, unless there is a lack of availability of a particular brand. As for booster brand guidance, more is expected later in the week.

“The risk is that you are going to have a side effect,” Barron said about getting a booster when they are available. “The benefit is that you are probably protected from getting COVID, which is a big deal.”

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