The move is the first publicly announced mix-and-match of a Chinese vaccine and a Western-developed shot, as a new preliminary Thai study raised doubts about the longer-term protection of the two-dose course Sinovacvaccine.
“This is to improve protection against the Delta variant and build a high level of immunity against the disease,” Health Minister Anutin Charnvirakul told reporters, adding that the second dose of AstraZeneca would come three or four weeks after the first Sinovac shot.
There have been no studies specifically on mixing Sinovac and AstraZeneca released, but a growing number of countries are looking at mix-and-match of different vaccines or giving a third booster dose amid concerns new and more contagious variants may escape approved vaccines.
Thailand now plans to give booster shots of imported mRNA vaccine to its frontline workers – who were given imported Sinovac before the locally manufactured AstraZeneca vaccine was available in June. Indonesia is considering similar boosters.
On Monday, a preliminary Thai study of 700 medical workers indicated that Sinovac’s protection rate as measured by antibody level ranged between 60% and 70% for the first 60 days after the second dose, but the rate steadily went down over time and appeared to halve every 40 days.
Thailand on Monday implemented its toughest coronavirus restrictions in more than a year in Bangkok and surrounding provinces, amid a fast-rising wave of the highly transmissible Alpha and Delta variants, with cases rising to nearly 10,000 per day and record deaths.
According to Reuters