HONG KONG (BLOOMBERG) - Young children who received two doses of China's Sinovac Biotech Ltd vaccine gained "modest" defences against Omicron infections and higher protection against developing severe cases of Covid-19, a study in Chile showed.
Researchers, who tracked about 490,000 children ages 3 to 5 years, estimated the Sinovac shot has effectiveness rates of 38 per cent against Covid-19, 65 per cent against hospitalisation, and 69 per cent against an infection severe enough to require admission to an intensive care unit.
The study took place during the Omicron outbreak in Chile between December and February and was conducted by researchers, mostly working for local universities as well as the country's health ministry.
The results, which were uploaded as a preprint on Research Square, have not undergone peer review yet offer insights into how the vaccine fares against the more-transmissible variant.
They also shed some light on the efficacy of Covid-19 vaccines in children, as the spread of Omicron led to more paediatric hospital admissions.
The rates of protection are substantially lower than recent preliminary estimates of the effectiveness of two doses of the Sinovac vaccine in children 6 to 16 years, when the Delta variant was predominant.
In that study, the estimated effectiveness was 75 per cent against Covid-19, 91 per cent for the prevention of hospitalisation, and 94 per cent against admission to an ICU.
Earlier lab studies from across the world have shown that Omicron significantly dented the effectiveness of various vaccines, including the more potent messenger RNA shots.
Research from Hong Kong has found a booster dose of an mRNA vaccine can improve the protective levels of antibodies against omicron, while a third Sinovac shot cannot.
Sinovac's inactivated shot is one of the world's most widely used Covid inoculations, with over 260 million doses administered as of mid-March.
The vaccine has also been approved for use among children as young as three in 14 jurisdictions, ranging from mainland China and Hong Kong to Thailand and Brazil, according to the company.
