Safety of primary immunization using inactivated SARS-CoV-2 vaccine (CoronaVac®) among population aged 3 years and older in a large-scale use: A multi-center open-label study in China.

Objective: To evaluate the safety of primary immunization using CoronaVac® among population aged 3 years and above in a large-scale use.

Method: A multi-center open-label study was carried out in 11 provinces of China. Individuals aged 3 years and older who had no history of COVID-19 vaccination or had received only one dose of CoronaVac® were enrolled in this study. Adults and elderly with or without underlying medical conditions(UMCs) were also recruited. Eligible participants received one or two doses of CoronaVac® with an interval of 28 days. Demographic information, vaccination and the occurrence of adverse events were recorded by participants or guardians using data collection system designed for this study. All adverse events occurred within 6 months after the second dose of vaccination were collected. The incidence of adverse events that cannot be ruled out as being caused by the vaccine were calculated to assess the safety of CoronaVac®. This study is registered with ClinicalTrials. Gov (NCT04911790 and NCT04992208).

Results: A total of 162,691 participants have been included in this study and 89.50 % had finished primary immunization. Among adults and elderly, people with UMCs accounted for 25.85 %, with the top five disease being hypertension, diabetes, chronic gastritis, coronary heart disease(CHD) and kidney stone. The overall incidence of adverse reactions (ARs) within 6 months after the second vaccination was 2.70 %, with incidence for children and adolescents, adults, and elderly being 2.03 %, 3.46 %, and 1.90 %, respectively. Most ARs were mild (grade 1). Pain at the injection sites, fatigue, induration/swelling, and headache were the most common symptoms, occurring in 1.64 %, 0.46 %, 0.31 % and 0.24 %, respectively. No serious adverse events related to vaccines were reported. No adverse events of special interest (AESIs) were identified. For children and adolescents, children aged 3-5 years had the highest incidence of ARs of 3.29 %. The incidence of ARs among those aged 18 years and older with and without UMCs were 2.81 % and 2.99 %, respectively, with no statistical significance between two groups(P = 0.089). And people with coronary heart disease had higher AR incidence compared to those with other UMCs, but the most common symptoms was pain at the injection site.

Conclusion: CoronaVac® is safe in a large-scale use and shows well-tolerance for children and adolescents and people with underlying medical conditions. Further studies need to be conducted to explore the relation of ARs incidence to age or different kinds of UMCs.