(WJW) – People who are immunocompromised may be eligible for a fourth dose of the COVID-19 vaccine, reportedly as early as this week.

According to updated recommendations from the Centers for Disease Control and Prevention, people who have a weakened immune system should get an additional primary shot if they received a Pfizer-BioNTech or Moderna vaccine.

“After completing the primary series, some moderately or severely immunocompromised people should get an additional primary shot,” the CDC stated, adding that anyone eligible for an additional primary shot should get it first before getting a booster.

That means the fourth shot is actually considered the booster, for which some could be eligible now.

According to the CDC, the additional primary dose is intended to improve a person’s response to their primary vaccine series. In contrast, a booster shot would be given when the vaccine primary series is completed “to enhance or restore protection against COVID-19 that may have decreased over time,” the agency said.

The CDC endorsed a third dose of the Pfizer and Moderna shots on Aug. 13 as part of the primary immunization, not a booster, The New York Times reported.

As of last week, the booster is now recommended five months after the third primary shot. The CDC’s previous guidance — announced in October — was six months before getting the booster.

It hasn’t been recommended yet for the Johnson & Johnson’s Janssen single shot.

According to the CDC, people are considered moderately or severely immunocompromised if they are receiving cancer treatment, an organ transplant, a stem cell transplant, advanced or untreated HIV infection, or moderate or severe primary immunodeficiency.

Several media outlets, including The New York Times, are reporting some can get the shot as early as this week. Ultimately, patients should talk with their health care providers about what’s right for them.