Transmission of SARS‐CoV‐2 in standardised first few X cases and household transmission investigations: A systematic review and meta‐analysis

Abstract

We aimed to estimate the household secondary infection attack rate (hSAR) of SARS‐CoV‐2 in investigations aligned with the WHO Unity Studies Household Transmission Investigations (HHTI) protocol. We conducted a systematic review and meta‐analysis according to PRISMA 2020 guidelines. We searched Medline, Embase, Web of Science, Scopus and medRxiv/bioRxiv for “Unity‐aligned” First Few X cases (FFX) and HHTIs published 1 December 2019 to 26 July 2021. Standardised early results were shared by WHO Unity Studies collaborators (to 1 October 2021). We used a bespoke tool to assess investigation methodological quality. Values for hSAR and 95% confidence intervals (CIs) were extracted or calculated from crude data. Heterogeneity was assessed by visually inspecting overlap of CIs on forest plots and quantified in meta‐analyses. Of 9988 records retrieved, 80 articles (64 from databases; 16 provided by Unity Studies collaborators) were retained in the systematic review; 62 were included in the primary meta‐analysis. hSAR point estimates ranged from 2% to 90% (95% prediction interval: 3%–71%; I2 = 99.7%); I2 values remained >99% in subgroup analyses, indicating high, unexplained heterogeneity and leading to a decision not to report pooled hSAR estimates. FFX and HHTI remain critical epidemiological tools for early and ongoing characterisation of novel infectious pathogens. The large, unexplained variance in hSAR estimates emphasises the need to further support standardisation in planning, conduct and analysis, and for clear and comprehensive reporting of FFX and HHTIs in time and place, to guide evidence‐based pandemic preparedness and response efforts for SARS‐CoV‐2, influenza and future novel respiratory viruses.

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

“…32,33 It can be difficult to make direct comparisons between studies that are conducted in different countries and settings due to the unique features of local epidemics and adaptations required for implementation. 34 Studies should be interpreted in light of the local epidemiology and context−considerations should be made for the surveillance and contact tracing capacity, local incidence of COVID-19 cases during study implementation, predominant circulating SARS-CoV-2 variant, the timing and duration of the study, and study design including case ascertainment strategies and specimen sampling methods. Characteristics of individuals affected by COVID-19 and recruited into the study such as socioeconomic status, occupation and size of recruited households may also be significantly different across these studies, and therefore may influence aggregate outcomes.…”

Estimating Asymptomatic and Symptomatic Transmission of the COVID‐19 First Few Cases in Selenge Province, Mongolia

“…Despite robust individual case interviews and contact‐tracing records, missing data was the main challenge in this study. In the future, developing more country‐specific preplanned FFX to improve pandemic preparedness tailors public health and social measures around the evidence generated [ 34 ]. The local data collection capacity should also be modernized to assure data quality.…”

Transmissibility and severity of COVID‐19 in a humanitarian setting: First few X investigation of cases and contacts in Juba, South Sudan, 2020

“…Despite this, higher SAR estimates were also observed in other African countries, including Madagascar (SAR 29.6%; 95% CI: 23.0%, 36.9%) 25 and Ethiopia (SAR 45.2%; 95% CI: 38.6%, 52.1%) 26 . A recent meta‐analysis highlighted the substantial heterogeneity in SAR estimates obtained from FFX investigations across the globe 27 . This heterogeneity may be attributed to differences in culture, pandemic activity or implementation of FFX protocols throughout the COVID‐19 pandemic and highlights the need for further standardisation of the FFX investigation protocol 27 …”

“…A recent meta‐analysis highlighted the substantial heterogeneity in SAR estimates obtained from FFX investigations across the globe 27 . This heterogeneity may be attributed to differences in culture, pandemic activity or implementation of FFX protocols throughout the COVID‐19 pandemic and highlights the need for further standardisation of the FFX investigation protocol 27 …”