Effects of Influenza Vaccination in the United States During the 2017–2018 Influenza Season
Authors: Rolfes Melissa A , Flannery Brendan , Chung Jessie R , O’Halloran Alissa , Garg Shikha , Belongia Edward A , Gaglani Manjusha , Zimmerman Richard K , Jackson Michael L , Monto Arnold S , Alden Nisha B , Anderson Evan , Bennett Nancy M , Billing Laurie , Eckel Seth , Kirley Pam Daily , Lynfield Ruth , Monroe Maya L , Spencer Melanie , Spina Nancy , Talbot H Keipp , Thomas Ann , Torres Salina M , Yousey-Hindes Kimberly , Singleton James A , Patel Manish , Reed Carrie , Fry Alicia M ,   US Influenza Vaccine Effectiveness (Flu VE) Network, the Influenza Hospitalization Surveillance Network, and the Assessment Branch, Immunization Services Division, Centers for Disease Control and Prevention, McLean Huong Q , King Jennifer P , Nowalk Mary Patricia , Balasubramani G K , Bear Todd M , Hickey Robert , Williams John V , Reis Evelyn C , Moehling Krissy K , Eng Heather , Jackson Lisa A , Smith Michael , Raiyani Chandni , Clipper Lydia , Murthy Kempapura , Chen Wencong , Reis Michael , Petrie Joshua G , Malosh Ryan E , McSpadden E J , Segaloff Hannah E , Cheng Caroline K , Truscon Rachel , Johnson Emileigh , Lamerato Lois E , Rosenblum Bret , Ford Samantha , Johnson Monika , Raviotta Jonathan M , Sax Terrie , Steele Jonathan , Susick Michael , Chabra Rina , Garofolo Edward , Iozzi Philip , Kevish Barbara , Middleton Donald B , Urbanski Leonard , Ponder Teresa , Crumbaker Todd , Iosefo Iosefo , Sleeth Patricia , Gandy Virginia , Bounds Kelsey , Kylberg Mary , Rao Arundhati , Fader Robert , Walker Kimberley , Volz Marcus , Ray Jeremy , Price Deborah , Thomas Jennifer , Wehbe-Janek Hania , Beeram Madhava , Boyd John , Walkowiak Jamie , Probe Robert , Couchman Glen , Motakef Shahin , Arroliga Alejandro , Kaniclides Anne , Bouldin Emerson , Baker Christoph , Berke Kimberly , Smith Mackenzie , Rajesh Niharika , Alleman Elizabeth , Bauer Sarah , Groesbeck Michelle , Brundidge Kristyn , Hafeez Neha , Jackson Jayla , Anastasia Ian , Kadoo Gabriel , Petnic Sarah , Ryan Alison , Maslar Amber , Meek James , Chen Rona , Stephens Samantha , Thomas Stepy , Segler Suzanne , Openo Kyle , Fawcett Emily , Farley Monica , Martin Andrew , Ryan Patricia , Sunkel Robert , Lutich Taylor , Perlmutter Rebecca , Grace Brittany , Blood Timothy , Zerrlaut Cindy , McMahon Melissa , Strain Anna , Christensen Jamie , Angeles Kathy , Butler Lisa , Khanlian Sarah , Mansmann Robert , McMullen Chelsea , Pradhan Eva , Manzi Katarina , Felsen Christina , Gaitan Maria , Long Krista , Fisher Nicholas , Hawley Emily , O’Shaughnessy Rory , Scott Magdalena , Crawford Courtney , Schaffner William , Markus Tiffanie , Leib Karen , Dyer Katie , Santibanez Tammy , Zhai Yusheng , Lu Pengjun , Srivastav Anup , Hung Mei-Chuan 
Published: January 2019

Abstract

Background
The severity of the 2017–2018 influenza season in the United States was high, with influenza A(H3N2) viruses predominating. Here, we report influenza vaccine effectiveness (VE) and estimate the number of vaccine-prevented influenza-associated illnesses, medical visits, hospitalizations, and deaths for the 2017–2018 influenza season.

Methods
We used national age-specific estimates of 2017–2018 influenza vaccine coverage and disease burden. We estimated VE against medically attended reverse-transcription polymerase chain reaction–confirmed influenza virus infection in the ambulatory setting using a test-negative design. We used a compartmental model to estimate numbers of influenza-associated outcomes prevented by vaccination.

Results
The VE against outpatient, medically attended, laboratory-confirmed influenza was 38% (95% confidence interval [CI], 31%–43%), including 22% (95% CI, 12%–31%) against influenza A(H3N2), 62% (95% CI, 50%–71%) against influenza A(H1N1)pdm09, and 50% (95% CI, 41%–57%) against influenza B. We estimated that influenza vaccination prevented 7.1 million (95% CrI, 5.4 million–9.3 million) illnesses, 3.7 million (95% CrI, 2.8 million–4.9 million) medical visits, 109 000 (95% CrI, 39 000–231 000) hospitalizations, and 8000 (95% credible interval [CrI], 1100–21 000) deaths. Vaccination prevented 10% of expected hospitalizations overall and 41% among young children (6 months–4 years).

Conclusions
Despite 38% VE, influenza vaccination reduced a substantial burden of influenza-associated illness, medical visits, hospitalizations, and deaths in the United States during the 2017–2018 season. Our results demonstrate the benefit of current influenza vaccination and the need for improved vaccines.