UNC Health Talk

3 Things You Need to Know About COVID-19 Boosters

Editors note: For the latest guidance on boosters, see “Simplifying Boosters: How to Know When to Get One.” 


A much larger swath of the population recently became eligible for COVID-19 vaccine boosters, but you need to meet certain criteria to get this supplemental third shot.

First, you have to have received the second dose of the Pfizer-BioNTech vaccine six months ago or longer. Second, you must be at least one of three things: age 65 or older, age 18 or older and at higher risk for COVID-19 because of a medical condition, or age 18 or older and at high risk of exposure because of where you work or live. (Note: If you are immunocompromised because of circumstances such as cancer treatment or an organ transplant or you are taking immunosuppressing medications, you have been eligible for a booster with the Pfizer or Moderna vaccines since early September.)

“All three vaccines available in the U.S. continue to show high levels of protection against becoming severely ill with COVID-19. However, there are signals that those vaccinated earlier may have increasing vulnerability to being infected with the virus,” says UNC Health infectious diseases specialist David A. Wohl, MD. “A supplemental dose is intended to shore up immunity in those for whom any waning of protection would be most concerning, like older people and those more at risk for severe disease.”

Boosters for older and high-risk adults who received the Moderna and Johnson & Johnson vaccines are soon to come, public health officials say.

“Right now, we have more data on boosting the Pfizer vaccine than the other two. This is unfortunate, but I expect we will hear soon about boosting for those who received Moderna or Johnson & Johnson,” Dr. Wohl says. “Meanwhile, the good news is these vaccines continue to work. Close to 95 percent of those in our ICUs with COVID-19 are unvaccinated.”

For now, younger people in good health who don’t work in a high-risk setting do not need a booster, according to the Food and Drug Administration. That could change as time goes on.

Whether you qualify for a booster now or later, here are three facts to know.

1. Boosters are common for many vaccines.

Your body’s immunity to many viruses, whether acquired naturally or through a vaccine, declines over time.

A booster shot is an additional dose of a vaccine that gives a “boost” to your immunity and provides better protection from disease. Many routine vaccines require more than one shot to maintain immunity. For example, adults should get a Tdap booster every 10 years; that protects against tetanus, diphtheria and pertussis (whooping cough).

“With a booster, the immunity that has already been established by a vaccine is stimulated again,” Dr. Wohl says. “So in a way, the booster serves as a reminder to the immune system’s memory, which can fade over time after vaccination.”

Researchers are still trying to figure out how long COVID-19 vaccines are effective. The FDA decision reflects emerging evidence that efficacy may fade more quickly for older people, and that some immunocompromised people may not mount an adequate initial immune response.

2. Some people can get a COVID-19 booster now, and others can expect to get one eventually.

In early September, boosters were made available to people with significantly compromised immune systems who initially received the Pfizer or Moderna vaccines. The FDA and the Centers for Disease Control and Prevention have provided guidance on who qualifies as being sufficiently immunocompromised, and this includes people who have received a transplant, are undergoing cancer therapy, have advanced or untreated HIV infection, or are taking medications that suppress the immune system.

The latest authorization expands that group significantly to include the following:

  • People who received two doses of either the Pfizer or Moderna vaccines at least one month ago and are moderately to severely immunocompromised. Pfizer recipients must be at least 12 years old, and Moderna recipients must be 18 and older.
  • People who received two doses of the Pfizer vaccine at least six months ago and are:
    • Age 65 or older
    • Ages 18 to 65 and have a medical condition that increases the risk for severe COVID-19, such as diabetes, being overweight, obesity or lung, heart or kidney disease
    • Ages 18 to 65 and work or live in a group setting such as a school, nursing home or shelter, or have a job that requires face-to-face contact with the public

Right now, people who initially received the Johnson & Johnson vaccine are not eligible for a booster. Study data are expected shortly that will help the FDA determine how best to boost immunity in people who received this vaccine. Similarly, for those who initially received the Moderna vaccine and are not immunocompromised, a booster dose has not been authorized by the FDA but should be soon.

“We’re all going to get boosters. Starting with the immunocompromised makes sense and then those whose protection may be waning, such as the people who got vaccinated earliest,” Dr. Wohl says.

3. Everyone should be wearing masks.

Because of the much higher transmissibility of the delta variant, Dr. Wohl says, it’s important for even fully vaccinated people to wear masks indoors when around people who might not be vaccinated and who are outside of their immediate household bubbles.

The CDC is now recommending masking for vaccinated people in regions where COVID-19 has been surging, which is most of the country. The spread of the delta variant among unvaccinated people means that some will pass the virus on to those who are vaccinated. Fortunately, the vast majority of those who are vaccinated and get infected will have no or minimal symptoms.

“Delta is now almost 100 percent of the circulating virus, and each person with delta on average infects five or more other people. This is why it is incredibly important that all of us mask up when we are indoors anywhere outside of our homes, including at stores, school or work,” Dr. Wohl says. “My recommendation to everyone, regardless of your vaccine status, is to wear a mask indoors when you’re outside of your bubble.”

This article was originally published July 30, 2021 and updated September 29, 2021. 


Visit unchealthcare.org/vaccine to schedule a COVID-19 vaccine and for the latest information on the COVID-19 vaccines.