(Bloomberg) -- Young children who received two doses of China’s Sinovac Biotech Ltd. vaccine gained “modest” defenses against omicron infections and higher protection against developing severe cases of Covid-19, a study in Chile showed.

Researchers, who observed about 490,000 children ages 3 to 5 years, estimated the Sinovac shot has effectiveness rates of 38% against Covid-19, 65% against hospitalization, and 69% 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. It also sheds some light on the efficacy of Covid-19 vaccines in children, as the spread of omicron led to more pediatric 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 in those children was 75% against Covid-19, 91% for the prevention of hospitalization, and 94% 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.


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