According to Reuters, 618 Thai healthcare workers who received two doses of the Sinovac vaccine, from April to July, have been infected with Covid-19, the country's health ministry stated on July 11.
In addition, a 30-year-old nurse has died, the Bangkok Post reported, while another is in critical condition.
Thailand has changed its vaccine policy after this was reported. Instead of two Sinovac shots, people will now receive the AstraZeneca vaccine after their first Sinovac shot.
Vaccinated with Sinovac
Thus far, 677,348 Thai healthcare workers, which is most of the country's medical staff, have received two doses of Sinovac, since February.
Thailand only began receiving doses of the Oxford-AstraZeneca vaccine in June.
It is expecting 1.5 million doses of the Pfizer-BioNTech vaccine later this month, along with an additional 20 million shots that will arrive after October.
Thai medical expert claims Sinovac is less effective against Delta variant
Thai PBS World further reported that two doses of Sinovac could boost neutralising antibodies to 80 per cent to 90 per cent.
These were the findings of a joint study by the chief of Chulalongkorn University's Centre for Emerging Infectious Diseases, Thiravat Hemachudha, with a virologist at Thailand's National Center for Genetic Engineering and Biotechnology (BIOTECH) and the Central Chest Institute of Thailand .
The study also found that while Sinovac could provide protection against the Alpha variant, the vaccine allegedly could not "fend off" the Delta variant. According to Reuters, there is a lack of "detailed data" on Sinovac's effectiveness against the Delta variant for peer review.
Nikkei Asia reported that within Bangkok, more than half of the infections are from the Delta variant.
Hemachudha was also quoted by the Bangkok Post as stating that Sinovac was at its most effective against Covid-19 for up to 30 days after the second dose.
However, immunity against Covid-19 drops to 30 per cent to 40 per cent beyond that point, he added.
As such, Hemachudha has called for the government to urgently provide a booster shot to medical workers involving a different vaccine.
Booster shot should be from Oxford-AstraZeneca or a mRNA vaccine
In comparison, two doses of the AstraZeneca vaccine conferred neutralising antibodies of over 90 per cent, against the Delta variant, the study further found.
Hemachudha also highlighted the finding that two doses of Sinovac, plus a booster dose of AstraZeneca, could prevent the Delta infection better than two doses of Sinovac.
However, this is still less effective than two doses of AstraZeneca.
The BBC reported on July 12 that Thailand has changed its vaccine policy.
Instead of two Sinovac shots, people will now receive the AstraZeneca vaccine after their first Sinovac shot.
Health workers already fully vaccinated with Sinovac will also receive a third booster dose. This can be either the AstraZeneca vaccine, or an mRNA vaccine like Pfizer-BioNTech.
This third dose will be given three to four weeks after their second Sinovac jab, said the country's National Infectious Disease Committee on Monday.
Top photo Thiravat Hemachudha Facebook