CDC extends interval between COVID vaccine doses for exceptional cases

Patients can space out the two doses of the coronavirus vaccine by up to six weeks if it’s "not feasible" to follow the shorter recommended window, according to updated guidance from the Centers for Disease and Control and Prevention.

Driving the news: With the prospect of vaccine shortages and a low likelihood that supply will expand before April, the latest changes could provide a path to vaccinate more Americans — a top priority for President Biden.

What they're saying: “What the CDC is saying, sometimes, the situation is stressed where it’s very difficult to be exactly on time,” Biden's chief medical adviser Anthony Fauci told CNN. “So we’re saying, you can probably do it six weeks later, namely, two additional weeks."

• "Quite frankly, immunologically, I don’t think that’s going to make a big difference," Fauci added.
• The CDC's “intention is not to suggest people do anything different, but provide clinicians with flexibility for exceptional circumstances," agency spokesperson Kristen Nordlund told the New York Times.

Details: The CDC recommends getting the second dose three weeks after the first for the Pfizer-BioNTech vaccine, and suggests a four-week window between the two doses of Moderna's vaccine.

• The two doses should be administered as close to that recommended schedule as possible, the CDC says.
• Of note: There is “limited data on efficacy” of the vaccines beyond that interval, according to the new guidance, but if the second dose is administered later “there is no need to restart the series.”
• The updated guidance also says "every effort should be made to determine which vaccine product was received as the first dose, in order to ensure completion of the vaccine series with the same product."
• "In exceptional situations in which the first-dose vaccine product cannot be determined or is no longer available," any available mRNA vaccine can be used for the second dose, the guidance adds.

The big picture: The U.S. failed to meet its goal of vaccinating 20 million people by the end of December.

• In his first days in office, Biden promised an aggressive campaign to ramp up vaccine production, aiming to deliver 100 million vaccinations in 100 days.
• The new president's "wartime" coronavirus strategy includes invoking the Defense Production Act to increase vaccine supply.
• Fauci has said the U.S. could achieve herd immunity by fall if Biden's vaccine rollout goes as planned.

Go deeper: The most vulnerable Americans aren't getting enough vaccine information