Learnings from the Australian first few X household transmission project for COVID-19

Adrian J Marcato; Andrew J Black; Camelia R Walker; Dylan Morris; Niamh Meagher; David J Price; Jodie McVernon; Australian FFX Household Transmission Project Group

doi:10.1016/j.lanwpc.2022.100573

Learnings from the Australian first few X household transmission project for COVID-19

Lancet Reg Health West Pac. 2022 Nov:28:100573. doi: 10.1016/j.lanwpc.2022.100573. Epub 2022 Sep 5.

Authors

Affiliations

¹ Department of Infectious Diseases, The University of Melbourne, at the Peter Doherty Institute for Infection and Immunity, Melbourne, Australia.
² School of Mathematical Sciences, The University of Adelaide, Adelaide, Australia.
³ School of Mathematics & Statistics, The University of Melbourne, Melbourne, Australia.
⁴ Centre for Epidemiology & Biostatistics, Melbourne School of Population & Global Health, The University of Melbourne.
⁵ Murdoch Children's Research Institute, Melbourne, Australia.

Abstract

Background: First Few "X" (FFX) studies provide a platform to collect the required epidemiological, clinical and virological data to help address emerging information needs about the COVID-19 pandemic.

Methods: We adapted the WHO FFX protocol for COVID-19 to understand severity and household transmission dynamics in the early stages of the pandemic in Australia. Implementation strategies were developed for participating sites; all household members were followed for 14 days from case identification. Household contacts completed symptom diaries and had multiple respiratory swabs taken irrespective of symptoms. We modelled the spread of COVID-19 within households using a susceptible-exposed-infectious-recovered-type model, and calculated the household secondary attack rate and key epidemiological parameters.

Findings: 96 households with 101 cases and 286 household contacts were recruited into the study between April-October 2020. Forty household contacts tested positive for SARS-CoV-2 in the study follow-up period. Our model estimated the household secondary attack rate to be 15% (95% CI 8-25%), which scaled up with increasing household size. Our findings suggest children were less infectious than their adult counterparts but were also more susceptible to infection.

Interpretation: Our study provides important baseline data characterising the transmission of early SARS-CoV-2 strains from children and adults in Australia, against which properties of variants of concern can be benchmarked. We encountered many challenges with respect to logistics, ethics, governance and data management. Continued efforts to invest in preparedness research will help to test, refine and further develop Australian FFX study protocols in advance of future outbreaks.

Funding: Australian Government Department of Health.

Keywords: COVID-19; Epidemiology; Household transmission; Infectious disease; Public health; SARS-CoV-2.