No antibody-dependent enhancement effect was observed during phase III clinical trials and mass inoculation of Sinovac Biotech's COVID-19 vaccine CoronaVac, Liu Peicheng, spokesman for Sinovac Biotech, said in a news briefing on Sunday.

ADE is a phenomenon in which a vaccine's mechanism to trigger an immune response also has the potential to amplify the infection, causing the disease to worsen instead of protecting the subject. This effect is observed in vaccines against some viruses, most notably in the dengue virus.

Liu said nearly 130 million doses of CoronaVac have been administered around the globe and there are no reports of ADE. Late-stage clinical trials of the vaccine were conducted in several countries, including Brazil, Indonesia, Turkey and Chile, and no instance of ADE was ever reported.