BANGKOK (NYTIMES) - Thailand said on Monday (July 12) that healthcare workers who had received the coronavirus vaccine made by Sinovac of China would also be inoculated with the Oxford-AstraZeneca or Pfizer-BioNTech shots to give them greater protection as concerns grow about more transmissible variants as well as about the waning immunity provided by Sinovac.
Mr Anutin Charnvirakul, Thailand's health minister, said people vaccinated with one dose of Sinovac should be given the AstraZeneca shot as the second dose three to four weeks later. Those who have already received both shots of the Sinovac vaccine, he said, should receive a booster shot "right away".
"This will build immunity against the virus to a high level more quickly," Mr Anutin said at a news conference.
Thailand is the latest foreign government to indicate doubts about the immunity provided by the Sinovac vaccine.
Last Friday, Indonesia said it would offer the Moderna vaccine as a booster to healthcare workers who had received two doses of the Sinovac shot.
Both countries are facing their most serious coronavirus outbreaks of the pandemic, driven by the highly contagious Delta variant that was first detected in India.
On Sunday, Thailand reported a record 9,418 new coronavirus infections, a day after it reported a record 91 coronavirus-related deaths.
For at least two weeks starting on Monday, the capital, Bangkok, and surrounding provinces will be under tight restrictions aimed at curbing the spread of the virus, including a curfew and a five-person limit on gatherings.
Most medical workers in Thailand were inoculated with the Sinovac vaccine after it was approved in February, with the AstraZeneca vaccine becoming available only recently.
Trial results have shown that the Sinovac shot is at least 51 per cent effective at preventing symptomatic disease, above the threshold set by the World Health Organisation, and even more effective at preventing hospitalisation and death.
But several countries that were among the earliest recipients of the Sinovac vaccine have reported that their healthcare workers have fallen ill with Covid-19 despite being fully vaccinated.
On Sunday, the Thai Health Ministry said that out of the 677,348 medical personnel who had received two doses of Sinovac, 618 had become infected, citing data from April to July. One nurse has died, and another medical worker is in critical condition.
"Breakthrough infections" - infections that happen even in individuals who are fully vaccinated - can happen with any vaccine. But governments are especially concerned when it happens to healthcare workers, especially at a time when their hospitals are already under strain.
On Sunday, Dr Thiravat Hemachudha, a specialist in clinical, virological and immunological studies at Chulalongkorn University in Bangkok, said that a study of people who had received two doses of the Sinovac vaccine showed that their level of antibodies, at 70 per cent, was "barely efficacious" against the Alpha variant first detected in Britain or against the Delta variant.
Dr Thiravat said it was imperative that the Thai government gave front-line medical workers booster shots because they faced higher risks of infection. Thailand is producing the AstraZeneca shots locally, the only country in South-east Asia to do so. It does not have any Pfizer vaccines on hand but expects to receive a donation of 1.5 million doses from the United States this month.
While studies suggest that most Covid-19 vaccines are effective against the Delta variant, which the WHO says is likely to become the dominant form of the virus worldwide in the coming months, less is known about the Sinovac vaccine.
One of China's top public health researchers, Dr Zhong Nanshan, has said that a study of 160 people infected with the Delta variant in the southern city of Guangzhou showed that China's vaccines, developed by Sinovac and another company, Sinopharm, were 69 per cent effective in preventing infection among close contacts, according to Xinhua, the state-run news agency. Sinovac has not provided any data.