But in the case of limited supply, the Pfizer vaccine can be given as the second dose for those who have received the AstraZeneca vaccine for their first jab, with the consent of the people to be vaccinated, the MOH said in its latest guidelines.

But the mixing could slightly increase the reaction after one gets vaccinated, warned the ministry, adding that the spacing between the two doses should be 8-12 weeks.

The MOH advised against using the Moderna vaccine or other vaccines for the second shot for those who have received the AstraZeneca vaccine in their first jab.

It emphasised that those given the first shot of the Sinopharm, Pfizer and Moderna vaccines must be given the booster shot of the same type, with the spacing as recommended by their manufacturers.

As of August 3 morning, Vietnam had administered nearly 7 million doses of COVID-19 vaccine, with 6.2 million people having received one dose and 700,000 being fully vaccinated.

In another development, Vietnam will begin clinical trials of a COVID-19 vaccine developed by the US company Arcturus Therapeutics, whose manufacturing rights have been secured by VinBioCare, a subsidiary of VinGroup.

Phase I is scheduled to begin on August 8 when the mRNA vaccine will be administered to 100 volunteers at the Hanoi Medical University. Phase II will be conducted on 300 volunteers and Phase III will involve 20,600 volunteers.

VinBioCare is planning to build a plant to manufacture this vaccine at the Hoa Lac High-Tech Park on the outskirts of Hanoi.