GUANGZHOU, China

Inactivated COVID-19 vaccines developed by China curbed the spread of the Delta variant during a May outbreak in Guangzhou city in south China, a study has shown.

Led by reputed Chinese epidemiologist Zhong Nanshan, researchers from the Guangzhou Center for Disease Control and Prevention found that two shots of the vaccines provided an efficacy of 59 per cent against COVID-19 caused by the Delta variant, 70.2 per cent against moderate forms of the disease, and 100 per cent against severe cases.

Meanwhile, with an efficacy of 13.8 per cent, single-dose vaccination did not provide sufficient protection.

Due to effective containment of the epidemic, testing vaccine efficacy has been challenging in the Chinese mainland. A real-world setting in the study has offered an opportunity to determine the effectiveness of two existing inactivated vaccines against the Delta strain, said the researchers.

The study collected data from 628 participants, including 153 confirmed COVID-19 cases caused by the Delta variant and 475 close contacts of the confirmed cases.

The 153 confirmed cases were diagnosed between May 18 and June 20. Among them, six had severe COVID-19, and 10 had critical COVID-19. There were no deaths during the study period.

Among the vaccinated cases, 61.3 per cent accepted two shots of the CoronaVac vaccine developed by Sinovac Life Sciences Co, Ltd, based in Beijing, and 27.5 per cent accepted two shots of the Sinopharm vaccine. Another 10.4 per cent received a mix of vaccines from both companies, and 0.8 per cent had missing information on the vaccination type.

According to the research paper, the protective effect of the two-dose vaccination against the Delta strain reached 72.5 per cent among the study participants aged 40 to 59 years. The vaccine efficacy was also higher in females.

There were no severe and critical cases or deaths among the vaccinated study participants. None of the 16 severe or critical cases were vaccinated. The paper speculated that the inactivated vaccines could prevent severe COVID-19.