JAKARTA - A study has shown that Sinovac's Covid-19 vaccine CoronaVac is 85 per cent effective against symptomatic illness and 92 per cent against hospitalisation among older people in Jakarta, the Indonesian government said on Friday (Aug 6) night.

The China-made vaccine is 95 per cent effective in preventing deaths, a chart from the Indonesian health ministry showed.

The effectiveness against symptomatic illness is reduced to 35 per cent if only the first jab is given.

The figures are based on a study involving 86,936 Jakarta residents aged 60 and above between March and April this year.

Vaccine effectiveness refers to the performance of a vaccine in a population under a real-world situation, while vaccine efficacy refers to the performance of a vaccine in a controlled clinical trial situation, according to the World Bank.

The study also revealed that chances of a vaccinated older person dying of Covid-19 are up to 15 times less than someone who is not vaccinated.

A separate study by the health ministry on 25,374 medical workers in the capital between January and March this year showed that CoronaVac was 96 per cent effective against hospitalisation, 94 per cent against infection and 100 per cent in preventing deaths.

Jakarta's figures on CoronaVac's effectiveness were higher than those reported by Chile, where it was found to be 58.5 per cent effective in preventing symptomatic illness among 8.6 millions of Chileans who received the shots between February and July, Reuters reported.

The vaccine was 86 per cent effective against hospitalisation, and 86 per cent effective in preventing deaths between February and July, Reuters cited health official Rafael Araos in a press conference on Tuesday.

Indonesia aims to inoculate 214 million people - or about three-quarters of the population, including those aged between 12 and 18 - by the end of this year. So far, about 20 million have received both shots.

President Joko Widodo has said that Indonesia is conducting a three-pronged approach in combating the Covid-19 wave: boosting vaccination; imposing strict health protocols; and ramping up testing and tracing.

"Firstly, we speed up vaccination especially in the regions with high mobility and economic activities... Testing and tracing would be followed by isolation and treatment," Mr Widodo said on Monday, when he announced an extension of a partial lockdown for a week, mainly in parts of Java - including Jakarta - and Bali.

He pledged that the country would set up more centralised quarantine facilities and guaranteed the availability of medicine and oxygen supplies.

The lockdown that began on July 3 covers parts of Java and Bali, and 15 other cities and regencies in places such as Sumatra and Sulawesi.

It has led to the suspension of most activities and closure of non-essential public places, including malls, places of worship and parks.