[Technical guidelines for seasonal influenza vaccination in China (2023-2024)].

Influenza is an acute respiratory infectious disease that is caused by the influenza virus, which seriously affects human health. The influenza virus has frequent antigenic drifts that can facilitate escape from pre-existing population immunity and lead to the rapid spread and annual seasonal epidemics. Influenza outbreaks occur in crowded settings, such as schools, kindergartens, and nursing homes. Seasonal influenza epidemics can cause 3-5 million severe cases and 290 000-650 000 respiratory disease-related deaths worldwide every year. Pregnant women, infants, adults aged 60 years and older, and individuals with comorbidities or underlying medical conditions are at the highest risk of severe illness and death from influenza. China has experienced a influenza epidemic season dominated by A (H1N1) pdm09 subtype from mid-February to the end of April 2023, and the intensity was slightly higher than the epidemic year before the COVID-19. We may face the risk of interaction or co-circulation of respiratory infectious diseases such as COVID-19 and influenza during the coming season. Annual influenza vaccination is an effective way to prevent influenza, reduce influenza-related severe illness and death, and reduce the harm caused by influenza-related diseases and the use of medical resources. The currently approved influenza vaccines in China include trivalent inactivated influenza vaccine (IIV3), quadrivalent inactivated influenza vaccine (IIV4), and trivalent live attenuated influenza vaccine (LAIV3). IIV3 and IIV4 are produced as a split virus vaccine and subunit vaccine; LAIV3 is a live, attenuated virus vaccine. The influenza vaccine is a non-immunization program vaccine, which means that residents are voluntarily vaccinated. China CDC has issued "Technical guidelines for seasonal influenza vaccination in China" every year from 2018 to 2022. Over the past year, new research evidence has been published at home and abroad, and new influenza vaccines have been approved for marketing in China. To better guide the prevention and control of influenza and vaccination in China, the National Immunization Advisory Committee (NIAC) Technical Working Group (TWG), Influenza Vaccination TWG updated and revised the 2022-2023 technical guidelines with the latest research progress into the "Technical guidelines for seasonal influenza vaccination in China (2023-2024)." The new version has updated five key areas: (1) new research evidence－especially research conducted in China-has been added, including new estimates of the burden of influenza disease, assessments of influenza vaccine effectiveness and safety, and analyses of the cost-effectiveness of influenza vaccination; (2) policies and measures for influenza prevention and control were issued by the National Health Commission of the People's Republic of China and National Disease Control and Prevention Administrationy over the past year; (3) influenza vaccines approved for marketing in China this year; (4) composition of trivalent and quadrivalent influenza vaccines for the 2023-2024 northern hemisphere influenza season; and (5) recommendations for influenza vaccination during the 2023-2024 influenza season. The 2023-2024 guidelines recommend that all people aged 6 months and above who have no contraindications should get the influenza vaccination. For adults aged ≥18 years, co-administration of inactivated SARS-CoV-2 and influenza vaccines in separate arms is acceptable regarding immunogenicity and reactogenicity. For people under 18 years of age, there should be at least 14 days between influenza vaccination and COVID-19 vaccination. The guidelines express no preference for influenza vaccine type or manufacturer-any approved, age-appropriate influenza vaccines can be used. Combining the influenza epidemic tendency and the prevention and control strategy of multiple diseases, the technical guidelines recommend priority vaccination of the following high-risk groups during the upcoming 2023-2024 influenza season to minimize harm from influenza: (1) healthcare workers, including clinical doctors and nurses, public health professionals, and quarantine professionals; (2) adults ≥60 years of age; (3) individuals with comorbidities; (4) people living in nursing homes or welfare homes and staff who take care of vulnerable, at-risk individuals; (5) pregnant women; (6) children 6-59 months of age; (7) family members and caregivers of infants under 6 months of age; and (8) people who work in nursery institutions, primary and secondary schools, and supervision places. Children 6 months to 8 years of age who receive inactivated influenza vaccine for the first time should receive two doses, with an inter-dose interval of 4 or more weeks. Children who previously received the influenza vaccine and anyone aged 9 years or older need only one dose. LAIV is recommended only for a single dose regardless of the previous influenza vaccination. Vaccination should begin as soon as influenza vaccines become available, and preferably should be completed before the onset of the local influenza season. Repeated influenza vaccination during a single influenza season is not recommended. Vaccination clinics should provide immunization services throughout the epidemic season. Pregnant women can receive inactivated influenza vaccine at any stage of pregnancy. These guidelines are intended for use by staff of CDCs, healthcare workers, maternity and child care institutions and immunization clinic staff members who work on influenza control and prevention. The guidelines will be updated periodically as new evidence becomes available.