China's Sinovac vaccine may be better than previously thought: It was 94% effective at preventing symptomatic COVID-19 in a real-world study, Indonesian officials said

• Sinovac's COVID-19 vaccine was an estimated 98% effective at preventing death in Indonesian health workers.
• It was also 96% effective at preventing hospitalization, Indonesian officials said.
• The data suggests the vaccine may be more effective than previously thought.

The two-dose COVID-19 vaccine developed by Chinese biotech Sinovac is highly effective at preventing hospitalization and death, Indonesian health officials said Wednesday.

The vaccine, called Coronavac, was an estimated 98% effective at preventing death and 96% effective at preventing hospitalization, Pandji Dhewantara, an Indonesian health ministry official, said in a press briefing.

The stats were based on 128,000 health workers who received the shot in Jakarta, the capital of Indonesia, and were monitored between January and March.

Dhewantara said that 94% of workers hadn't caught symptomatic COVID-19, and protection kicked in 7 days after the second dose.

The study compared vaccinated people with non-vaccinated people to estimate the effectiveness of the shot.

The results haven't been published in a medical journal or scrutinized by experts.

The vaccine costs about $30 per dose, according to Chinese state media, and can be stored at normal fridge temperatures, which could make it a useful option for low- and middle-income countries struggling to secure vaccines. As of April 12, more than 180 million CoronaVac doses have been sent to 30 low-and-middle income countries, including Brazil, Chile, and the Philippines.

About 22.5 million COVID-19 vaccine doses have been given in Indonesia, with just under 5% of Indonesians receiving at least one dose, mostly from Sinovac, according to Oxford University's Our World in Data.

Better than trials?

Indonesia's results could mean that Coronavac works better in real-life than expected.

Late-stage trial results from Brazil released April 12 of more than 12,000 health workers showed that the shot was 50.7% effective against symptomatic COVID-19. The numbers in the Brazil trial weren't large enough to draw conclusions about its effectiveness against severe COVID-19.

Sinovac said that it required more information about Indonesia's study to be able to comment on the results, per Bloomberg.

Helen Petousis-Harris, a vaccinologist at the University of Auckland, told Bloomberg that trials can fail to predict the overall impact of vaccines, something that can only be seen in the real world after widespread use.

"Reducing the bulk of disease is not only essential to save lives but also to reduce the chances of problematic variants appearing," she said.

Other possible reasons for the disparity between results include that the median age of the Indonesian study was 31, whereas the Brazilian trial included people over 60 - about 5% of participants.

In Turkey, CoronaVac was 83.5% effective at preventing symptomatic COVID-19 in a study of more than 10,000 participants aged between 19 and 59.

There were also a relatively low number of new cases in Indonesia during the study period. Between January and March, there were between 18 to 47 daily new coronavirus cases per million people in Indonesia, according to Our World in Data. For comparison, the number of daily new infections in the US during the same period was between 193 and 758 cases per million.

The Brazilian trial was conducted when cases were surging.

Yin Weidong, Sinovac CEO, told Bloomberg in a previous interview that real world results and scientific data from clinical trials would allow the world to judge the vaccine.

"We encourage our partners and governments in countries where our vaccine is being used to release such data as soon as possible," he said.