1. School of Mathematics and Statistics, Fuzhou University, Fuzhou 350116, China
2. Fujian Provincial Center for Disease Control and Prevention, Fuzhou 350012, China
3. Key Laboratory of Operations Research and Control of Universities in Fujian, Fuzhou University, Fuzhou 350116, China
4. Center for Applied Mathematics of Fujian Province, Fuzhou University, Fuzhou 350116, China
5. Complex Models Research Center, Shanxi University, Taiyuan 030006, China
6. Department of Mathematics and Statistics, University of Strathclyde, Glasgow G1 1XH, UK
7. Public Health School, Fujian Medical University, Fuzhou 350122, China