Interim Estimates of 2019-20 Seasonal Influenza Vaccine Effectiveness - United States, February 2020

• Published in: MMWR. Morbidity and mortality weekly report 2020-02, Vol.69 (7), p.177-182
• Main Authors: Dawood, Fatimah S, Chung, Jessie R, Kim, Sara S, Zimmerman, Richard K, Nowalk, Mary Patricia, Jackson, Michael L, Jackson, Lisa A, Monto, Arnold S, Martin, Emily T, Belongia, Edward A, McLean, Huong Q, Gaglani, Manjusha, Dunnigan, Kayan, Foust, Angie, Sessions, Wendy, DaSilva, Juliana, Le, Shoshona, Stark, Thomas, Kondor, Rebecca J, Barnes, John R, Wentworth, David E, Brammer, Lynnette, Fry, Alicia M, Patel, Manish M, Flannery, Brendan
• Format: Article
• Language: English
• Subjects: Adolescent; Adult; Aged; Child; Child, Preschool; Diseases; Female; Full Report; Humans; Infant; Influenza; Influenza A Virus, H1N1 Subtype - isolation & purification; Influenza A Virus, H3N2 Subtype - isolation & purification; Influenza B virus - isolation & purification; Influenza vaccines; Influenza Vaccines - administration & dosage; Influenza Vaccines - immunology; Influenza, Human - epidemiology; Influenza, Human - prevention & control; Influenza, Human - virology; Male; Medical research; Medical schools; Middle Aged; Population Surveillance; Respiratory tract diseases; Seasons; United States - epidemiology; Vaccination; Vaccines; Young Adult
• ISSN: 0149-2195; 1545-861X
• DOI: 10.15585/mmwr.mm6907a1

During the 2019-20 influenza season, influenza-like illness (ILI)* activity first exceeded the national baseline during the week ending November 9, 2019, signaling the earliest start to the influenza season since the 2009 influenza A(H1N1) pandemic. Activity remains elevated as of mid-February 2020. In the United States, annual vaccination against seasonal influenza is recommended for all persons aged ≥6 months (1). During each influenza season, CDC estimates seasonal influenza vaccine effectiveness in preventing laboratory-confirmed influenza associated with medically attended acute respiratory illness (ARI). This interim report used data from 4,112 children and adults enrolled in the U.S. Influenza Vaccine Effectiveness Network (U.S. Flu VE Network) during October 23, 2019-January 25, 2020. Overall, vaccine effectiveness (VE) against any influenza virus associated with medically attended ARI was 45% (95% confidence interval [CI] = 36%-53%). VE was estimated to be 50% (95% CI = 39%-59%) against influenza B/Victoria viruses and 37% (95% CI = 19%-52%) against influenza A(H1N1)pdm09, indicating that vaccine has significantly reduced medical visits associated with influenza so far this season. Notably, vaccination provided substantial protection (VE = 55%; 95% CI = 42%-65%) among children and adolescents aged 6 months-17 years. Interim VE estimates are consistent with those from previous seasons, ranging from 40%-60% when influenza vaccines were antigenically matched to circulating viruses. CDC recommends that health care providers continue to administer influenza vaccine to persons aged ≥6 months because influenza activity is ongoing, and the vaccine can still prevent illness, hospitalization, and death associated with currently circulating influenza viruses as well as other influenza viruses that might circulate later in the season.