(CBS Denver) – Both Pfizer and Moderna say it’s likely everyone will need booster shots within 12 months of the second doses of their vaccines. CBS Denver Medical Editor Dr. Dave Hnida says that’s because it’s starting to become clear that COVID immunity does “tend to wane a little bit” over time after being fully vaccinated.

Vail Health Hospital pharmacy technician Rob Brown practices measuring the exact dosage for a mock Covid-19 vaccine in the sterile compounding room in the pharmacy on Dec. 8, 2020 in Vail. (credit: Helen H. Richardson/MediaNews Group/The Denver Post via Getty Images)

“We’ve been kind of wondering about this for quite some time, and it does look like this is going to wind up being the case,” Hnida said during his weekly question & answer session on CBSN Denver.

Hnida was asked about whether the COVID vaccine will wind up being somewhat like the annual flu shot.

“Variants are a big thing when it comes to COVID, and they’re a big thing when it comes to influenza. That’s why we get a different influenza vaccine every year, in other words different booster shots,” he said. “So we may wind up seeing a deal … where we get an extra vaccination, or on the other hand we may wind up having to have an annual event just like with the flu vaccine.”

Hnida was then asked whether people will always need to stick with the same vaccine maker they started with. If you get Pfizer the first time around, do you need to get to Pfizer for your booster shot?

“Considering the fact that these are new vaccines that may very well be the case — we just may want to play it safe and stable. If you got Pfizer before we’ll give you the booster with Pfizer,” Hnida said. “On the other hand, there is this thing in immunity and vaccinations where we actually find that with certain diseases, you can actually get better immunity with different types of vaccines.”

Hnida said different vaccines can give a patient what’s called a “stacked immunity” and he says it would not surprise him if mixing and matching vaccines becomes a recommended method down the line.