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 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 Sinovac vaccine.
"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.
The announcement came a day after Thailand's health ministry said
618 medical workers out of 677,348 personnel who received two doses
of the Sinovac vaccine became infected from April to July. One nurse
died.
Neighbouring Indonesia has also reported breakthrough infections
among medical and frontline workers who are fully inoculated with
the Sinovac vaccine.
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.
"From our research, if our medical staff received two doses of
Sinovac ... they should definitely get a third booster shot," Sira
Nanthapisal, a researcher at Thammasat University's Faculty of
Medicine, told Reuters. The researchers have yet to release their
full study data.
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 "They can do that either
between AstraZeneca or Pfizer when it arrives,
and we will continue to monitor their
antibodies," Sira said.
An AstraZeneca representative declined to
comment on Thailand's decision, saying only that
vaccination policy is a matter for each country
to decide.
Sinovac did not respond to requests for comment
on Monday.
Last month, Sinovac spokesman Liu Peicheng told
Reuters preliminary results from blood samples
of the vaccinated showed a three-fold reduction
in neutralizing effect against the Delta variant
and suggested a third Sinovac shot could elicit
more durable antibody reaction.
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.
The measures, initially for two weeks, include
widespread suspensions by airlines and bus
firms, a curfew, mall closures and a five-person
limit on gatherings.
The vast majority among the total 345,027 cases
and 2,791 fatalities have been since April after
nearly a year of largely controlling the virus,
but there has been a slow start to its mass
vaccination rollout that only began last month.
(Writing by Kay Johnson. Editing by Martin
Petty)
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