Colorado’s vaccine providers should begin giving a third dose of the Moderna and Pfizer vaccines to some immunocompromised residents, the state health department said Friday night after the federal government endorsed the move.

The Centers for Disease Control and Prevention announced Friday it was supporting a booster dose to moderately and severely immunocompromised Americans, after another federal agency approved the expansion of the vaccines’ approval.

In a statement, CDC director Rochelle P. Walensky said research shows three concerning trends related to people with poor immune systems: They do not always build the same level of immunity as others; fully vaccinated, immunocompromised people “have accounted for a large proportion” of (COVID-19) hospitalizations” among vaccinated people; and they are more likely to spread the virus once infected.

“At a time when the Delta variant is surging, an additional vaccine dose for some people with weakened immune systems could help prevent serious and possibly life-threatening COVID-19 cases within this population,” she wrote, referring to the COVID-19 strand that accounts for nearly every new case in Colorado.

Coloradans and other Americans who aren’t immunocompromised “are adequately protected and do not need an additional dose of COVID-19 (vaccine) at this time,” said Janet Woodcock, the acting commissioner of the Food and Drug Administration.

The new dose should be administered at least four weeks after the latter of the first two doses is completed, the state health department said, and the third jab should be the same vaccine — Moderna or Pfizer — that the patient received for their first two inoculations.

According to the CDC, those who qualify for the third dose include people receiving tumor or blood cancer treatment; those who received an organ transplant and accompanying treatment to suppress the immune system; residents who received a stem cell treatment within the past two years; those who are taking medicine to suppress the immune system for other conditions; those with conditions that lead to moderate or severe primary immunodeficiency; and “advanced or untreated HIV” patients.

About 7 million adults in the U.S. are immunocompromised, including people with cancer, HIV and those on certain medications such as chemotherapy and high-dose corticosteroids. It’s unclear what other conditions besides solid organ transplant recipients make someone eligible for a third dose.

A nonpeer-reviewed study posted in June found that among a group of healthy people, 98% produced antibodies after vaccination, while only 37% of organ transplant patients, 55% of blood cancer patients, 82% of solid tumor cancer patients and 84% of those with autoimmune disorders developed the protective proteins.

In its own release sent Friday night, the state Department of Public Health and Environment said the state has “enough vaccine inventory” to support the third-dose regimen. The vaccination rate in Colorado is well above 70%, but uptake has dwindled consistently since the spring.

“We want to make sure Coloradans most at-risk of severe outcomes have the best protection they can against the deadly COVID-19 virus,” said Diana Herrero, deputy director of the disease control and public health response for the state health department. “Administering an additional dose of the vaccine for these Coloradans will help us increase their protection and prevent more severe illness, hospitalization, and death.”

Those Coloradans who qualify for a third dose “should be able to access them immediately at enrolled state and federal vaccine providers.” The department also recommends immunocompromised residents wear masks, maintain distance from others, and avoid crows and poorly ventilated areas.

For people who have received the single-dose Johnson & Johnson vaccine, there is no additional dose yet. Nearly 231,000 Coloradans have received that vaccine.

“There is not enough data at this time to determine whether immunocompromised people who received the Johnson & Johnson’s Janssen COVID-19 vaccine also have an improved antibody response following an additional dose of the same vaccine,” the CDC wrote on its website.

Vaccine manufacturers have said healthier people who received Moderna and Pfizer will eventually need a third shot to boost immunity, but federal officials are still gathering data. But the expansion of third doses to everyone vaccinated with the two-jab regimen is inevitable, said Anthony Fauci, the White House’s chief medical advisor.

“What we’re doing, literally, on a weekly and monthly basis is following cohorts of patients to determine if, when and whom should get it,” Fauci told the “Today Show” on Thursday “But right now at this moment, other than the immunocompromised, we’re not going to be giving boosters to people, but we will be following them very carefully and if they do need it, we’ll be ready to give it to them.”

The Associated Press contributed to this report.