Anthony Fauci, the U.S.’s top infectious-disease doctor, said Covid-19 vaccine booster shots should be given “reasonably soon” to people with weakened immune systems.

“We need to look at them in a different light,” Fauci said on CNN’s “Fareed Zakaria GPS” on Sunday. “We would certainly be boosting those people before we boost the general population that’s been vaccinated, and we should be doing that reasonably soon.”

Fauci spoke as debate grows over “breakthrough” infections among fully vaccinated people and whether approval should be given for booster shots. On Sunday, Israel, the first nation to roll out booster shots widely, said it had given more than 420,000 third shots to people 60 and over.

Fauci said most people who have compromised immune systems, including those with organ transplants or who are on chemotherapy, “never did get an adequate response” from their Covid-19 vaccination.

When asked if other groups should get booster shots, Fauci said the U.S. Centers for Disease Control and Prevention is ready to give such recommendations “as soon as” they see clear evidence to do so from the data.

The CDC has been tracking the level of durability of protection for the elderly, those in nursing homes and young people, month by month, he said. “As soon as they see that level of durability of protection goes down, then you will see the recommendation to vaccinate those individuals.”

Health officials don’t take breakthrough infections “lightly,” Fauci said. The delta variant, which is more contagious and is fueling the surge of U.S. cases to more than 100,000 a day, will produce “more” breakthrough cases.

He said the variant presents the additional problem that vaccinated people can also transmit the virus to someone else. That has led to the CDC revising its mask guidelines recently.

But, he stressed: “The vaccines are still doing what you originally want them to do -- to keep you out of the hospital to prevent you from getting seriously ill.”

A full approval from the Food and Drug Administration on the Covid-19 vaccines could arrive “within the next few weeks,” Fauci said on NBC’s “Meet the Press.” “I hope it’s within the month of August.”

Vaccines in the U.S. have so far been given under emergency-use approval -- a reason some people give for refusing to be vaccinated.