[Technical guidelines for seasonal influenza vaccination in China (2021-2022)].

Influenza is a respiratory infectious disease that can seriously affect human health. Influenza virus has frequent antigenic drifts that can facilitate escape from pre-existing population immunity and lead to rapid and widespread transmission. Seasonal influenza is characterized by annual epidemics and outbreaks in places of public gathering such as schools, kindergartens, and nursing homes. According to the World Health Organization (WHO), seasonal influenza causes 3 to 5 million severe cases and 290 000 to 650 000 deaths globally each year. Pregnant women, young children, the elderly, and persons with chronic medical conditions are at highest risk for severe illness and death from influenza virus infection. With the ongoing COVID-19 pandemic, SARS-CoV-2 may co-circulate with influenza and other respiratory viruses in the upcoming winter-spring influenza season. Seasonal influenza vaccination is the most effective way to prevent influenza virus infection and complications from influenza. China has several licensed influenza vaccines - trivalent inactivated influenza vaccines (IIV3), which include split-virus influenza vaccine and subunit vaccine; quadrivalent split-virus inactivated influenza vaccine (IIV4); and trivalent live attenuated influenza vaccine (LAIV3). With the exception of a few major cities, influenza vaccine is a non-program vaccine, which means that influenza vaccination is not included in China's Expanded Program on Immunization, and recipients must pay for influenza vaccine and its administration. China CDC has issued "Technical Guidelines for Seasonal Influenza Vaccination in China" every year from 2018 to 2020. This past year, there have been scientific and programmatic advances in prevention and control of seasonal influenza. To strengthen technical guidance for prevention and control of influenza and facilitate operational research on influenza vaccination, the National Immunization Advisory Committee (NIAC) Influenza Vaccination Technical Working Group (TWG) updated the 2020-2021 technical guidelines into the "Technical Guidelines for Seasonal Influenza Vaccination in China (2021-2022)." The new version has updates in five key areas: (1) new research evidence, especially from studies in China, on disease burden, vaccine effectiveness, vaccine-avoidable disease burden, vaccine safety monitoring, and cost-effectiveness and cost-benefit analyses, (2) policies and measures for influenza prevention and control that were issued by National Health Commission (NHC) in the past year, (3) licensure of a new seasonal influenza vaccine in time for the 2021-2022 season, (4) composition of the northern hemisphere trivalent and quadrivalent influenza vaccines for the 2021-2022 season, and (5) recommendations for influenza vaccination during the 2021-2022 influenza season. The recommendations specify that immunization clinics should provide influenza vaccine to all persons aged 6 months and above who are willing to be vaccinated and do not have contraindications; the interval between receipt of influenza vaccine and COVID-19 vaccine should at least 14 days; and there is no preference for one influenza vaccine over another for persons for whom more than one licensed, recommended, and appropriate vaccine is available. Considering the global COVID-19 pandemic and the need to decrease risk of influenza virus infection and minimize potential impact on COVID-19 prevention and control, we recommend the following target population priorities in preparation for the 2021-2022 influenza season: (1) healthcare workers, including clinical doctors and nurses, public health professionals, and quarantine professionals, (2) volunteers and staff who provide service and support for large events, (3) people living in nursing homes or welfare homes and staff who take care of vulnerable, at-risk individuals, (4) people who work in high population density settings, including teachers and students in kindergartens, primary, and secondary schools and prisoners and prison staff, and (5) people with high risk of complications from influenza, including adults ≥60 years of age, children 6-59 months of age, persons with certain chronic conditions, family members and caregivers of infants <6 months of age, and pregnant women and women who plan to become pregnant during the influenza season. Children 6 months through 8 years of age who have never received influenza vaccine or who have received only one lifetime dose require 2 doses of influenza vaccine that are administered at least 4 weeks apart. This recommendation applies to both IIV and LAIV. If children received 2 doses of influenza vaccine in the 2020-2021 influenza season or received more than 2 doses of influenza vaccine in prior influenza seasons, 1 dose of influenza vaccine is recommended. People more than 9 years old require only 1 dose of influenza vaccine. People should receive influenza vaccination by the end of October, and influenza vaccine should be offered as soon as it is available. For people unable to be vaccinated before the end of October, influenza vaccine will continue to be offered throughout the season. Influenza vaccine is recommended for pregnant women during any trimester of pregnancy. These guidelines are intended for use by staff of CDCs at all levels who work on influenza control and prevention; immunization clinic staff members; healthcare workers from departments of pediatrics, internal medicine, and infectious diseases; and staff of maternity and child care institutions at all levels. The guidelines will be periodically updated as new evidence becomes available.