Recent studies from Thailand, Indonesia and Chile have affirmed the efficacy of a COVID-19 vaccine produced by China's Sinovac Biotech.

A new study conducted by Thailand's Chulalongkorn University showed that 99.49 percent of Thai recipients of the vaccine, known as CoronaVac, had developed antibody responses four weeks after their second shots, the Bangkok Post reported.

Three weeks after the first shot, around 66 percent of the recipients had developed immune responses, according to the Center of Excellence in Clinical Virology of the Faculty of Medicine at the university.

"Two doses of CoronaVac were immunogenic in vaccinated volunteers," said Yong Poovorawan, head of the center, noting that the result is consistent with the preliminary findings previously reported in medical journal The Lancet Infectious Diseases last year, which found that the Chinese vaccine can induce a quick immune response.

The Chinese embassy in Thailand said China donated a new batch of 500,000 doses of Sinovac's vaccine to Thailand on Monday. Since the first batch of Chinese vaccines arrived on Feb 24, China has provided 4.5 million doses of China-made vaccines to Thailand.

An additional 1.5 million doses are expected to arrive in Bangkok soon, according to the embassy.

Tang Zhimin, director of China ASEAN Studies at the Panyapiwat Institute of Management in Bangkok, said the supply from China is "substantial and timely" for the ambitious vaccination plan proposed by the Thai government.

"Thailand was the first ASEAN country to import Sinovac jabs on a commercial basis," Tang told China Daily. "The support from China to Thailand during the pandemic contributes to bilateral ties."

Earlier, a study by the Indonesian Health Ministry showed that CoronaVac had effectively reduced the risk of COVID-19 symptoms in medical workers by 94 percent.

The study, from Jan 13 to March 18, involved 128,290 medical workers who were not infected with COVID-19, according to the research team's head Pandji Dhewantara. The study's conclusion was made after those medical workers received their second dose.

The study also concluded that the Sinovac vaccine was 96 percent effective in protecting medical workers from hospitalization resulting from COVID-19 infection, and 98 percent effective in preventing deaths from the virus.

In Santiago, Chile's Health Ministry said an updated study showed CoronaVac is 65.3 percent efficacious in preventing COVID-19.

Despite the COVID-19 variants in circulation, Rafael Araos, an adviser to the Undersecretariat of Public Health, said on Monday that "the vaccine is performing adequately".

The vaccine's efficacy in preventing hospitalization rose to 87 percent; in preventing admission to an intensive care unit, to 90.3 percent; and in preventing deaths caused by COVID-19, to 86 percent, Araos said.

Xinhua contributed to this report. Leonardus Jegho is a freelance journalist for China Daily.