China has reported 53 new symptomatic and 29 asymptomatic coronavirus cases as the authorities vowed to control the country’s month-long outbreak . The symptomatic cases included 24 that were locally transmitted – 18 in the eastern province of Jiangsu , five in Henan and one in Hunan – while 29 were from abroad. Of the 29 asymptomatic cases recorded on Saturday, 22 were from abroad and all of the seven locally transmitted infections were in Henan, the National Health Commission (NHC) said on Sunday. Kan Quancheng, director of Henan’s health commission, has pledged to contain the outbreak in the province “by the end of August”. The virus was first found there in a hospital in Zhengzhou. “[We have the] confidence and determination to fight this tough battle well, to control the outbreak as quickly as possible, to ensure that the outbreak is well controlled by the end of August, and to provide protection for economic and social development,” Kan said on Saturday, according to local media. The number of new infections has declined steadily in recent days , but the latest outbreak in China, which the authorities said was driven by the Delta variant , has again caused disruption to the world’s second-largest economy, forcing the closure of restaurants and entertainment venues and the cancellation of high-profile trade events. The authorities have since launched investigations into possible dereliction of duty among local government officials in Henan and Jiangsu provinces, where the latest infections have been centred. The Henan government said it was investigating Yucheng county over its “poor control” over the outbreak and suspected under-reporting of new infections, while 12 officials from Yangzhou in Jiangsu have been reprimanded for “inadequate performance of responsibilities” to control the outbreak. The 12 included including Zhao Guoxiang, the secretary of the Yangzhou health commission’s Communist Party committee. Xinjiang , in the far west, reported three asymptomatic cases on Sunday, which will be included in the national total released on Monday. The three cases were found during regular testing in the city of Alashankou, on the border with Kazakhstan, and 74 people identified as close contacts had been quarantined, local media reported. Meanwhile, there have been questions over whether Chinese vaccines are effective against the Delta variant. Gao Qiang, general manager of Sinovac Life Sciences, said that the level of protective antibodies that company’s vaccine produced against the Delta variant was roughly a sixth to a quarter of that for previous strains, but it could still make an “impact” in protecting those receiving it. “Judging from the recent situation in Guangdong, Nanjing and other places, the completion of two doses of vaccination can significantly reduce the risk of contracting severe illness [when] infected with the Delta strain,” Gao said in a Q&A published by Shanghai-based ThePaper.cn. Gao also said Sinovac had completed studies of a booster shot, and planned to submit clinical application materials for vaccines protecting against Delta variant strains in the third quarter of this year. “The third dose of vaccination is still as safe as the first and second doses,” Gao said. “At the same time, the level of neutralising antibodies can be rapidly increased within a week.” Separately, the Chinese medical products regulator has approved local trials for combined use of the Sinovac vaccine and a DNA vaccine developed by American biotech company Inovio, in the hope of achieving a stronger immune response. China had fully vaccinated more than 777 million people against Covid-19 as of Thursday, according to the NHC, with more than 1.8 billion doses having been given in total.