PHNOM PENH (REUTERS) - Cambodia will begin offering a booster shot against Covid-19, switching between the AstraZeneca and Chinese Covid-19 vaccines in an effort to fight the spread of the coronavirus in the South-east Asian country.

Prime Minister Hun Sen, launching the vaccination campaign for those aged 12 to 17, said on Sunday (Aug 1) that the third dose will be offered to between 500,000 and one million front-line workers as a priority.

"People who have already been vaccinated with Sinopharm and Sinovac should be given AstraZeneca as the third booster dose," he said in a speech which was broadcast on social media.

"For Cambodians who have been vaccinated with AstraZeneca, Sinovac should be given as the third dose," he added.

Mr Hun Sen also said the country will purchase more AstraZeneca vaccines through the global Covax vaccine-sharing scheme for the booster shots and the recent United States-funded Johnson & Johnson vaccines will be used to vaccinate indigenous peoples in north-eastern Cambodia.

Cambodia launched a lockdown in eight provinces bordering Thailand on Thursday last week in a bid to prevent the spread of the Delta variant of the coronavirus.

The World Health Organization (WHO) said this week that the Delta variant has been detected in migrants returning from Thailand through land borders and is now in the local community.

"We are racing against new variants. We must act today, and we must act fast to have no regrets tomorrow," said Dr Li Ailan, WHO Representative to Cambodia, in a statement on Saturday.

Cambodia managed to largely contain the virus for most of 2020, but an outbreak detected in late February has driven up total cases to 77,919, with 1,420 deaths.