WATERLOO -- The Region of Waterloo announced it will be ready to administer third doses of the COVID-19 vaccine to residents who are 50 years of age and older starting Dec. 13.

On Thursday, the province expanded booster eligibility to include the 50 and older age group 168 days after receiving their second shot. Previously, third doses had only been available for residents aged 70 and older, along with other high-risk demographics.

Kelly Grindrod, associate professor at the University of Waterloo School of Pharmacy said the booster shot will promote longer immunity, especially with the newly identified variants of concern, such as the Omicron strain.

"It's really about having longer and stronger protection," Grindrod told CTV News. "There is some weaning immunity and [the 50 and older age group] do need that third dose."

The shot will be available in many vaccination clinics across the region, but Grindrod recommends residents who are 50 and older book appointments at local pharmacies while larger clinics pivot to child vaccinations.

"We're focusing mostly on kids doses in the larger clinics like The Boardwalk and Pinebush. We're going to see a lot of the third doses mostly being done at pharmacies," Grindrod told CTV News. "As we get especially through this initial rush of the first kids [aged] five to 11 who are getting their vaccine, we're going to see a lot more availability of vaccine spots around the region, both in pharmacies and public health clinics."

Grindrod acknowledged Thursday’s eligibility announcement regarding the booster shot can cause confusion among residents.

"You're doing first doses, you're doing second doses, now you're doing a range of third doses,” Grindrod said. "People are coming in not quite sure when their eligible, if they're eligible, what they're getting."

Grindrod emphasized that residents will only by able to receive their booster shot no sooner than 168 days after getting their second dose and booking an appointment too early will make it more difficult for eligible candidates to get their third jab.

"It's an appointment spot that can't be used, it can often mean a wasted dose because it was a dose that was ready for the person that they didn't end up needing, and people who are eligible can have a hard time making appointments because it appears there are no appointments," Grindrod said.

Eligible residents can determine how soon they can receive their third dose on the Vaccine Hunters Canada website.

Vaccine appointments can be made on the Region of Waterloo website.