U.S. health officials are working to give a third COVID-19 shot as a booster for certain Americans with compromised immune systems who may be at greater risk from the Delta variant, White House chief medical advisor Dr. Anthony Fauci said Thursday.

The strategy, which will be administered by the Centers for Disease Control and Prevention, will give booster shots to people age 65 or older and people who are immunocompromised. More information on how this strategy will be administered is expected to be released by early September.

"It is extremely important for us to move to get those individuals their boosters and we are now working on that," Fauci said on a press call.

Fauci said rising cases resulting from the spread of the contagious Delta variant in the U.S. can be turned around with additional vaccinations.

He added that immunocompromised people may not be sufficiently protected by their existing COVID-19 vaccinations.

This move comes in direct opposition to the World Health Organization’s latest call: a moratorium on COVID-19 booster shots until at least the end of September to address the vaccine supply shortage in poor countries.

“I understand the concern of all Governments to protect their people from the Delta variant, but we cannot accept countries that have already used most of the global supply of vaccines using even more of it, while the world’s most vulnerable people remain unprotected,” Tedros Adhanom Gebreyesus, head of the World Health Organization, said in a statement.

There are growing concerns in the U.S. as Delta variant cases rise. The U.S. has seen an increase in hospitalizations and deaths by roughly 40%.

About half of the U.S., or 165 million people, have been fully vaccinated.