More than 350 doctors and medical workers have caught Covid-19 in Indonesia despite being vaccinated with Sinovac and dozens have been hospitalised, officials said, as concerns grow about the efficacy of some vaccines against more infectious variants.

"Most of the workers were asymptomatic and self-isolating at home," said Badai Ismoyo, head of the health office in the district of Kudus in central Java, but dozens were in hospital with high fevers and declining oxygen saturation levels.

Kudus, which has about 5,000 healthcare workers, is battling an outbreak believed to be driven by the more transmissible Delta variant which has pushed up its bed occupancy rates above 90 per cent.

Designated as a priority group, healthcare workers were among the first to be vaccinated when inoculations began in January. Almost all have received the Covid-19 vaccine developed by Chinese biopharmaceutical company Sinovac, the Indonesian Medical Association (IDI) says.