The U.S. Centers for Disease Control and Prevention (CDC) on Tuesday updated its booster shot recommended waiting period for people who completed their primary COVID-19 vaccination series for the Pfizer (PFE  )-BioNTech (BNTX  ) vaccine to five months, a month sooner than its previous guidance.

The federal agency's decision followed the U.S. Food and Drug Administration's (FDA) approval of the shorter time period between the primary vaccine series and a booster shot. Individuals who received the Moderna (MRNA  ) vaccine must still wait at least six months after their second dose before getting a booster, while recipients of the Johnson & Johnson (JNJ  ) vaccine only need to wait at least two months.

The CDC is also now recommending that children ages 5 to 11 who have moderate to severely compromised immune systems to receive a booster dose as part of their primary vaccination series of the Pfizer vaccine 28 days after their second dose, following the FDA's approval. Pfizer is the only recommended and authorized vaccine for children in that age group at this time.

"All we have done throughout the pandemic, we will continue to update our recommendations to ensure the best possible protection for the American people," said CDC Director Dr. Rochelle Walensky in a press statement. "Following the FDA's authorizations, today's recommendations ensure people are able to get a boost of protection in the face of Omicron and increasing cases across the country, and ensure that the most vulnerable children can get an additional dose to optimize protection against COVID-19."

The FDA concluded in its authorization earlier this week that children ages 5 to 11 who have undergone organ transplants or have conditions that compromise their immune system at a similar level may not produce enough COVID-neutralizing antibodies with only two shots compared to healthier children. A third shot added to their vaccine series would give these children the maximum benefit of vaccination, the agency said.

Both the FDA and CDC do not recommend a third dose for children between the ages of 5 and 11 with normal immune systems at this time.