Last checked at 
* Thailand used Sinovac vaccine for frontliners
* AstraZeneca vaccine available since June
* Delta variant on increase in Thailand
* New curbs imposed around capital
(Adds comments from a Thai researcher, Sinovac, AstraZeneca)
By Panarat Thepgumpanat and Panu Wongcha-um
BANGKOK, July 12 (Reuters) - Thailand will use AstraZeneca
Plc's COVID-19 vaccine as a second dose for those who
received Sinovac's shot as their first dose in a bid to
increase protection, it said on Monday.
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.
"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)
