More than 80,000 people in Shanghai have taken COVID-19 booster shots with different vaccines as sporadic community infections reappeared in the city.



Shanghai has officially launched the vaccination method, known as sequential immunization, which is said to be more effective at improving protection against the coronavirus disease.



People over 18 years old who are fully vaccinated with one of the three inactivated vaccines produced by Sinopharm and Sinovac Biotech can get a protein subunit COVID-19 vaccine made by Anhui Zhifei Longcom Biopharmaceutical or a viral vector vaccine from CanSino Biologics.



"Residents can choose either a different or the same vaccines for the booster shot," said Sun Xiaodong, deputy director of the Shanghai Center for Disease Control and Prevention.



The antibody levels of sequential immunization in the COVID-19 booster shots will rise four times to that of the three inactivated vaccines. The method is also more effective against the more transmissible Omicron variant of the coronavirus, according to studies.



A total of 88,600 people in Shanghai have chosen the sequential immunization as COVID-19 booster shot, Sun revealed.



He encouraged eligible seniors to take the COVID-19 vaccines or the booster shot as soon as possible.



More than four million residents over the age of 60 have received two jabs of COVID-19 vaccines. Among them, 2.6 million, or 45 percent of the city's total elderly population, have taken the booster shot, Sun told the city's COVID-19 press briefing on Monday.



Since the city restored its COVID-19 vaccination services in June, local authorities have set up temporary vaccination sites for some 145,000 people as well as vaccination vehicles for another 20,000. Medical staff have also provided door-to-door vaccination services for 8,000 seniors at local nursing homes, Sun pointed out.



Meanwhile, Shanghai designated its second high-risk area for COVID-19 along with a medium-risk area on Monday after another community infection was reported.



The 22-year-old woman, a confirmed COVID-19 case with mild condition, tested positive at a local fever clinic. She lives at the Shanggang No. 2 Community in the Pudong New Area, which has become a high-risk area, according to China's newly-updated COVID-19 control protocol.



More than 3,800 residents in the high-risk community will undergo a weeklong home quarantine with multiple polymerase chain reaction (PCR) tests.



A skin treatment center in Xintiandi, where she had been to in the last two weeks, was elevated to medium risk, Zhao Dandan, deputy director of the Shanghai Health Commission, said.



According to epidemiological investigation, she had also been to the Movie Hotel in Huangpu District and a KTV in Putuo District. These places have been quarantined and disinfected. Some 3,700 related people are under nucleic acid screening, including 125 close contacts of the patient.



There are currently two high-risk areas in Pudong and Putuo, respectively, along with five medium-risk areas in Jing'an, Fengxian, Putuo, Baoshan and Huangpu.



Other areas in the subdistricts or towns with high- or medium-risk areas have been defined as low-risk areas, according to the 9th edition of the protocol. People from low-risk areas must have a 48-hour PCR test report to leave Shanghai.



Community infections reappeared in Shanghai on both Sunday and Monday after the city had reported zero community cases for almost a week.



"The recent new infections had been to enclosed crowded sites where cluster infections are likely to happen," Zhao explained.



He called for enhancing precautionary measures such as health monitoring of employees, PCR report and health code checks as well as more frequent disinfection and ventilation.



Residents are urged to actively take COVID-19 vaccines, while obeying stipulations, including venue code scanning, temperature checks and epidemiological investigation, Zhao insisted.