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“You don’t choose the target with inactivated vaccines, you just throw in all these different antigens,” explains Jorge Kalil, a physician and immunologist at the University of São Paulo Medical School, Brazil.Ībout 2.4 billion doses of the Chinese vaccines have been administered in China, but almost 1 billion doses have gone to 110 other countries (see 'Biggest takers for China's vaccines'). By contrast, mRNA and viral-vector vaccines target the response to the spike protein, which is what the virus uses to enter human cells. Researchers say this type of vaccine seems to be less potent because it triggers an immune response against many viral proteins. This was on a par with the 63% efficacy reported for the University of Oxford–AstraZeneca’s viral-vector vaccine at the time of its WHO listing, but lower than the 90% and higher efficacies of the mRNA vaccines developed by Pfizer–BioNTech and Moderna.īoth the Chinese vaccines are inactivated vaccines, which use killed SARS-CoV-2 virus. In mid-2021, the World Health Organization (WHO) approved the shots for emergency use, on the basis of limited clinical-trial data suggesting that CoronaVac was 51% and Sinopharm 79% effective at preventing symptomatic disease. Not far behind is the vaccine developed in Beijing by state-owned Sinopharm (see 'The race to vaccinate'). Inactivated vaccinesĬoronaVac, produced by Beijing-based company Sinovac, is the world’s most widely used COVID-19 vaccine.