White House chief medical advisor Dr. Anthony Fauci said Tuesday that safety and efficacy data could be available within the next two weeks on pairing a primary regimen of Covid vaccines from one manufacturer with boosters from another.

Though the Centers for Disease and Prevention authorized Pfizer’s booster for seniors and the medically vulnerable on Friday, only recipients of Pfizer’s first two doses are eligible for their third shot. But the National Institutes of Health are on the verge of concluding trials that mixed boosters and initial doses from Pfizer, Moderna and Johnson & Johnson, Fauci said at a White House Covid briefing.

Fauci stated that the FDA must approve all mix-and match trials. While you shouldn’t try to outdo the FDA, at least the FDA has the data.

Data on Johnson & Johnson’s “mix-and-match study” could be ready within a week, while Pfizer’s trial might be completed by mid-October. Fauci said that data from Moderna’s mixed-and-match studies are available.

Pfizer and Moderna’s vaccines employ mRNA technology to combat Covid, while J&J’s uses an adenovirus to bolster the body’s immune response. Mixing and matching vaccines or boosters may give vaccine recipients more flexibility when choosing a third shot that will strengthen their waning immunity.

Fauci’s comments came just days after NIH Director Dr. Francis Collins said the agency was still reviewing the results of combining initial doses and boosters from separate vaccine makers. Collins added that Moderna and J&J were weeks away from the CDC and FDA evaluating their boosters.

The NIH announced the start of its mix-and-match vaccine trials on June 1, which included roughly 150 adults who were vaccinated with either Pfizer, Moderna or J&J. Three to four months following their first vaccine, participants received a third dose.