A clinical trial to mix and match Covid-19 vaccines will start in Korea to test whether it can prevent Covid-19 more effectively, the local health authorities said on Thursday.

Lee Yoo-kyung, a senior health official in charge of vaccination analysis, said studies of mixing Covid-19 vaccines in Spain, the U.K., Italy, Russia, and China and results would come out soon.

In Korea, the Korea National Institute of Health (KNIH) will conduct the dose mixing trial, giving a Pfizer dose to those who received the first dose of the AstraZeneca vaccine, Lee said.

About 400 to 500 people inoculated with the AZ vaccine will get a dose of the Pfizer vaccine, she added.

“This study will be used to find ways to increase the safety and effectiveness of Covid-19 vaccination,” Lee said.

However, military service members aged 30 or younger given the first dose of the AZ jab will get the second dose of the AZ vaccine, not a different vaccine, the health authorities said.