The Centers for Disease Control and Prevention (CDC) has updated its interim guidance on coronavirus vaccine administration to state that the first and second doses of approved jabs can be given up to six weeks apart. 

The CDC, however, continues to state that the second dose should not be given earlier than the recommended window of three to four weeks depending on which vaccine is given.

The agency published the changes without fanfare on Thursday. 

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"The second dose should be administered as close to the recommended interval as possible," the CDC stated. "However, if it is not feasible to adhere to the recommended interval, the second dose of Pfizer-BioNTech and Moderna COVID-19 vaccines may be scheduled for administration up to 6 weeks (42) days after the first dose. There are currently limited data on the efficacy of mRNA COVID-19 vaccines administered beyond this window. If the second dose is administered beyond these intervals, there is no need to restart the series."

The update comes amid a shortage in vaccine supply that has seen thousands of canceled appointments nationwide. Governors have raised concerns about available doses particularly after the Trump administration advised against reserving second doses.

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However, despite concerns of vaccine shortage, the CDC warns that the vaccines are not interchangeable, and should not be used as such.

"However, these mRNA COVID-19 vaccines are not interchangeable with each other or with other COVID-19 vaccine products," the update stated. "The safety and efficacy of a mixed-product series have not been evaluated. Both doses of the series should be completed with the same product."

The update also included guidance for patients who have a history of dermal fillers after instances of facial swelling occurred following vaccination. 

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"This appears to be temporary and can resolve with medical treatment, including corticosteroid therapy," the agency said, of the swelling. "MRNA COVID-19 vaccines may be administered to persons who have received injectable dermal fillers who have no contraindications to vacciantion."