Immunocompromised Americans who had a 3rd COVID-19 shot can now get a 4th, CDC says

• Many immunocompromised Americans became eligible for a fourth COVID-19 shot on Tuesday.
• The fourth dose can be any FDA-authorized shot, given six months after the third, the CDC said.

Most fully-vaccinated immunocompromised people in the US can now get a fourth COVID-19 shot after their third under new guidance from the Centers for Disease Control and Prevention (CDC).

Adults in the US with moderately or severely weakened immune systems who had vaccines from Pfizer-BioNTech or Moderna can now get a fourth dose six months after their third dose, the CDC said on Tuesday.

The fourth dose can be any COVID-19 vaccine authorized by the Food and Drug Administration (FDA), a list comprising Pfizer, Moderna, and Johnson & Johnson vaccines, the CDC said. For Moderna, the fourth dose should be halved, it said.

Immunocompromised people that received Johnson & Johnson's single-dose vaccine should get a second dose of an approved vaccine at least two weeks later, but not a third or fourth shot, per CDC guidance.

It's the first time that the CDC has recommended fourth doses for anyone.

The guidance doesn't apply to Americans at high risk of COVID-19 who have normal immune systems - these people are eligible for a third shot, a booster, at six months after they're fully vaccinated.

Roughly 3% of the US population is moderately or severely immunosuppressed and at risk of severe COVID-19, according to the CDC. These people often produce worse immune responses to vaccines than those who aren't immunocompromised, the CDC has previously said.

People that take steroids or drugs for transplants, and those with certain health conditions such as cancer and untreated HIV, would fit this criteria, according to the CDC.

In its latest guidance, the CDC said that a patient's clinical team was "best positioned to determine the appropriate timing of vaccination."

The CDC reiterated that immunocompromised people initially vaccinated with Pfizer or Moderna's shots should get a third dose at least 28 days after the second. The usual dose of Moderna's vaccine can be used, it said.