Those who are fully vaccinated but have a weakened immune system can get their third dose of a coronavirus vaccine at CVS and Walgreens starting this weekend.

For a majority of the population, responses to the COVID-19 vaccine have gone well. However, additional action may be needed to fight against the virus for the about 3% of the population who have weakened immune systems.

"A lot of people who are immunocompromised, people who had conditions that did not allow their immune system to respond to the vaccine, came down with breakthrough infections, says Dr. Harish Moorjani, an infectious disease specialist at Phelps Memorial Hospital.

The move comes hours after a Centers for Disease Control and Prevention advisory panel unanimously approved additional doses of vaccines for certain people with compromised immune systems.

Recent studies show many people with immunocompromised systems can have a weak response to the standard vaccine regimen of two shots. Those same studies found a third dose results in a higher response and better protection against the virus for those patients.

Moorjani says that this vaccine booster shot is necessary to help fight back against the pandemic.

“My advice to all immunocompromised people is go ahead and get the booster vaccine,” he says. "It protects people who get the booster shot who are otherwise not protected and can get breakthrough infections. But it also reduces the overall disease burden in the community."

A spokesperson for CVS says the third doses are only for those who received Pfizer or Moderna vaccines. The CDC recommends sticking with the same vaccine you originally received.

Those looking to receive the vaccine can schedule vaccination appointments on both the CVS and Walgreens websites.

Moorjani says people with underlying conditions shouldn't wait.

“If you want to protect your life, if you want to protect your health, go ahead and get this vaccine if you're immunocompromised,” he says.