The immunity of public health workers: observation from two waves SARS-CoV-2 Omicron variant endemic in Guangdong province, ChinaHuan Zhang1#, Lina Yi1#, Huifang Lin1#, Lirong Zou1, Pingping Zhou1, Chumin Liang1, Lilian Zeng1, Xue Zhuang1, Zhe Liu1, Jing Lu1, Jianfeng He1, Baisheng Li1*, Jiufeng Sun1,2,3,4,5*，Runyu Yuan1*.1Guangdong Workstation for Emerging Infectious Disease Control and Prevention, Guangdong Provincial Key Laboratory of Pathogen Detection for Emerging Infectious Disease Response, Guangdong Provincial Center for Disease Control and Prevention, Guangzhou 511430, China.

Background Global COVID-19 vaccination programs effectively contain the fast spread of the SARS-CoV-2. Characteristic the immunity status of returned populations will favor for understanding the achievement of herd immunity and long-term management of COVID-19 in China. Methods Returning travellers were recruited from 7 quarantine stations in Guangzhou, China. The immunity statuses of participants were determined through Competitive ELISA, Micro-Neutralization Assay and Enzyme-Linked FluoroSpot Assay. Results A total of 272 subjects were involved in questionnaire survey, in which 235 (86.4%) were returning ex-patriot Chinese and 37 (13.6%) were foreigners. Blood and throat swabs specimens were collected from each of 108 returning ex-patriot Chinese. The neutralizing antibody against SARS-CoV-2 was detected in ~90% of returning ex-patriot Chinese, either in the primary or the homologous and heterologous booster vaccination group. The serum NAb titers of them were significantly decreased against SARS-CoV-2 Omicron BA.5, BF.7, BQ.1 and XBB.1 compare with prototype virus. However, memory T cell responses including specific IFN-γ and IL-2 were no differences in either group. Smoking, drinking, SARS-CoV-2 infection, COVID-19 vaccination, and the time interval between last vaccination and the sampling were independent influencing factors for NAb titers against prototype SARS-CoV-2 and variants of concerns. The dose of vaccination was the unique common influencing factor for Omicron variants. Conclusions The herd immunity was established in returning ex-patriot Chinese who exposure to the complicated infection and vaccination circumstance. Domestic residents will benefit from booster of COVID-19 vaccines either in homologous and heterologous vaccination after re-opening of China, as well as breakthrough infection.