Global burden of respiratory infections associated with seasonal influenza in children under 5 years in 2018: a systematic review and modelling study
Xin Wang, You Li, Katherine L. O’Brien, Shabir A. Madhi, Marc‐Alain Widdowson, Peter Byass, Saad B. Omer, Qalab Abbas, Asad Ali, Alberta Amu, Eduardo Azziz‐Baumgartner, Quique Bassat, W. Abdullah Brooks, Sandra S. Chaves, Alexandria Chung, Cheryl Cohen, Marcela Echavarría, Rodrigo Fasce, Ángela Gentile, Aubree Gordon, Michelle J. Groome, Terho Heikkinen, Siddhivinayak Hirve, Jorge Jara, Mark A. Katz, Najwa Khuri‐Bulos, Anand Krishnan, Oscar de León, Marilla Lucero, John P. McCracken, Ainara Mira‐Iglesias, Jennifer C. Moïsi, Patrick K. Munywoki, Ourohiré Millogo, Fernando P. Polack, Manveer Rahi, Zeba Rasmussen, Barbara Rath, Samir K. Saha, Eric A. F. Simões, Viviana Sotomayor, Somsak Thamthitiwat, Florette K. Treurnicht, Marylene Wamukoya, Lay‐Myint Yoshida, Heather J. Zar, Harry Campbell, Harish Nair, Harish Nair, Harry Campbell, Xin Wang, You Li, Alexandria Chung, Manveer Rahi, Qalab Abbas, Asad Ali, Zulfiqar A Bhutta, Bushra Saeed, Sajid Soofi, Mohammad Tahir Yousafzai, Anita K. M. Zaidi, Alberta Amu, Elizabeth Awini, Eduardo Azziz‐Baumgartner, Henry C. Baggett, Sandra S. Chaves, Nong Shang, Stephanie J. Schrag, Marc‐Alain Widdowson, Stefano Tempia, Quique Bassat, Miguel Lanaspa, Sozinho Acácio, W. Abdullah Brooks, Amanda J. Driscoll, Maria Deloria Knoll, Katherine L. O’Brien, Christine Prosperi, Abdullah H Baqui, Luke C. Mullany, Peter Byass, Cheryl Cohen, Anne von Gottberg, Orienka Hellferscee, Florette K. Treurnicht, Sibongile Walaza, Doli Goswami, Mustafizur Rahman, Nicholas E. Connor, Shams El Arifeen, Marcela Echavarría, Débora Natalia Marcone, Noelia Reyes, Andrea Gutiérrez, Iván Rodríguez, Olga López, David Gomez Ortiz, Nathaly González, Ángela Gentile, María Del Valle Juárez
Abstract
BACKGROUND: Seasonal influenza virus is a common cause of acute lower respiratory infection (ALRI) in young children. In 2008, we estimated that 20 million influenza-virus-associated ALRI and 1 million influenza-virus-associated severe ALRI occurred in children under 5 years globally. Despite this substantial burden, only a few low-income and middle-income countries have adopted routine influenza vaccination policies for children and, where present, these have achieved only low or unknown levels of vaccine uptake. Moreover, the influenza burden might have changed due to the emergence and circulation of influenza A/H1N1pdm09. We aimed to incorporate new data to update estimates of the global number of cases, hospital admissions, and mortality from influenza-virus-associated respiratory infections in children under 5 years in 2018. METHODS: We estimated the regional and global burden of influenza-associated respiratory infections in children under 5 years from a systematic review of 100 studies published between Jan 1, 1995, and Dec 31, 2018, and a further 57 high-quality unpublished studies. We adapted the Newcastle-Ottawa Scale to assess the risk of bias. We estimated incidence and hospitalisation rates of influenza-virus-associated respiratory infections by severity, case ascertainment, region, and age. We estimated in-hospital deaths from influenza virus ALRI by combining hospital admissions and in-hospital case-fatality ratios of influenza virus ALRI. We estimated the upper bound of influenza virus-associated ALRI deaths based on the number of in-hospital deaths, US paediatric influenza-associated death data, and population-based childhood all-cause pneumonia mortality data in six sites in low-income and lower-middle-income countries. FINDINGS: In 2018, among children under 5 years globally, there were an estimated 109·5 million influenza virus episodes (uncertainty range [UR] 63·1-190·6), 10·1 million influenza-virus-associated ALRI cases (6·8-15·1); 870 000 influenza-virus-associated ALRI hospital admissions (543 000-1 415 000), 15 300 in-hospital deaths (5800-43 800), and up to 34 800 (13 200-97 200) overall influenza-virus-associated ALRI deaths. Influenza virus accounted for 7% of ALRI cases, 5% of ALRI hospital admissions, and 4% of ALRI deaths in children under 5 years. About 23% of the hospital admissions and 36% of the in-hospital deaths were in infants under 6 months. About 82% of the in-hospital deaths occurred in low-income and lower-middle-income countries. INTERPRETATION: A large proportion of the influenza-associated burden occurs among young infants and in low-income and lower middle-income countries. Our findings provide new and important evidence for maternal and paediatric influenza immunisation, and should inform future immunisation policy particularly in low-income and middle-income countries. FUNDING: WHO; Bill & Melinda Gates Foundation.