Comparison of the incidence and risk factors of COVID-19 and influenza associated acute respiratory illnesses: Results of the SHIVERS-II, III, IV prospective community cohort study
Authors: Huang Q Sue , Wood Tim , Aminisani Nayyereh , Kvalsvig Amanda , Baker Michael G , Nghiem Nhung , Seeds Ruth , Jennings Tineke , Jelley Lauren , Tan Chor Ee , O’Neill Meaghan , Utekar Srushti , Geoghegan Jemma L , Winter David , Turner Nikki , Dowell Tony , Balm Michelle , Grant Cameron C , Nesdale Annette , Dobinson Hazel C , Daniells Karen , McIntyre Peter , Widdowson Marc-Alain , Thomas Paul G , Webby Richard J ,   the SHIVERS investigation team, Bocacao Judy , Bird Bryden , Johnston Helen , Slater Tegan , Ahmad Farjana , Sam Mai Ahn , Glampe Elaisa , Davey Garbriella , Rensburg Megan , Cueto Jort , Caballero Ernest , John Joshma , Penghulan Emmanuel , Cairns Bree , Aizupuru Sasha , Ryan Helen , Thoms Leonora , Emmerton Leigh , Ammundsen Donna-Maree , Bennington Karen , Dineen Fiona , Sullivan Adele , Stamm Olivia , Currin Danielle , Raphael Akeena , Kawakami Pam , Ryan Mary , Marull Maritza , Bradshaw Amy , Berquist Klarysse , Gebbie Clare , England Ryan , Yugovich Olivia , Subbaraj Manogna , Suresh Meghna , Danielewicz Jessica , Patel Dhanisha , Min Jason , Forsythe Bethany , Harbison Sally-Ann , Kerr Laura , Lin Susan , Robson Beth , Scholes Paula , Talalima Sarah , Boyle Rachel 
Published: February 2025

Abstract

Background
While severe outcomes among hospitalised patients with COVID-19 and influenza are well described, comparative studies on community transmission and milder illnesses associated with COVID-19 and influenza are lacking.

Methods
We compared incidence, risk/protective factors, and clinical features among prospective community cohort participants with PCR-confirmed COVID-19-associated and influenza-associated acute respiratory illnesses (ARI) from 7-February to 2-October 2022 in Wellington, New Zealand.

Findings
The crude COVID-19-associated ARI incidence was 59/100 person-years (PY). The adjusted cumulative incidence for COVID-19 [77/100-PY;95%CI,75-80] was 4.5 times higher than for influenza [17/100-PY;95%CI,15-19]. The proportion of children (0-17 years) with COVID-19 of all COVID-19 cases was substantial but smaller than those of influenza [402/1229 (33%) vs 173/255 (68%), p&lt;0.0001]. The highest incidence of COVID-19 was among adolescents (12-17 years) [109/100-PY;95%CI,97-119] and non-Māori/Pacific [83/100-PY;95%CI,80-86] whereas the highest influenza incidence was among children (1-4 years) [49/100-PY;95%CI,40-58] and Māori [35/100-PY;95%CI,28-43].
Adolescents (12-17 years) had 2.5 times higher peak COVID-19 incidence (5.9/100) than adults ≥18 years (2.4/100). Adolescents with two doses of the COVID-19 vaccines had 75% greater risk of COVID-19 infection [hazard ratio:1.75,95%CI,1.40-2.20] compared to adults with three doses.
Vaccination, age, ethnicity, and household size were independent protective/risk factors for COVID-19 or influenza.
Participants with COVID-19, compared with influenza, were less likely to access healthcare or experience febrile/severe illnesses, but more likely to report sore throat, headache, myalgia, and taste/smell loss.

Interpretation
As the world transitions to COVID-19 endemicity, estimating disease burdens in community settings becomes important to understand complete disease pyramids, risk factors and clinical progression for informing countermeasures.