(Bloomberg) -- Chile will start to vaccinate residents with a third dose against coronavirus next week in a campaign that mixes shots from different providers, as the government seeks to protect the population from the delta variant.

Starting on Aug. 11, people 55 and older who received two doses of Sinovac Biotech Ltd.’s vaccine earlier this year will start to receive an AstraZeneca shot, health undersecretary Paula Daza said in a press conference Thursday.

In September, the population under the age of 55 that’s already been inoculated with the China-made vaccine will receive a booster from Pfizer-BioNTech. Meanwhile, children as young as three will be eligible for their first vaccines once health authorities have granted approval, Health Minister Enrique Paris said without specifying dates.

Read more: Covid Shots for Chilean Children Under 12 Seen Within Weeks

Chile is reinforcing a vaccination campaign that’s delivered two doses to about 65% of its population. Virus case counts and hospitalizations have plunged since early June, allowing for the roll-back in restrictions. Still, recent studies show the Sinovac shot loses some efficacy over time, and officials are concerned about the delta variant that’s caused major outbreaks from the U.S. to Asia.

This week, Sinovac announced plans to open a vaccine plant in Chile that will also serve other countries in Latin America.

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