FAYETTEVILLE, Ark. (KNWA/KFTA) — Many Arkansans are now eligible to get the Pfizer booster shot, but those who got Moderna or the Jansen vaccine must wait a little longer. One of the country’s preeminent doctors said the wait shouldn’t be too long.

Dr. Francis Collins is the Director of the National Institutes of Health (Maryland). He said people who got non-Pfizer vaccines cannot “mix” shots, meaning they can’t get the Pfizer booster. Collins said he got the Moderna vaccine, too, but for people who got the Pfizer vaccine at least half a year ago, Collins said to get a booster when possible.

“It’s coming, be a little patient,” Collins said. “Meanwhile, we’re not recommending that you mix and match. You kind of stay with the one you went to the dance with. If you started with Pfizer right now, stick with Pfizer.”