SARS-CoV-2 infections in migrants and the role of household overcrowding: A causal mediation analysis of Virus Watch data
Authors: Boukari Yamina , Beale Sarah , Nguyen Vincent Grigori , Fong Wing Lam Erica , Burns Rachel , Yavlinsky Alexei , Hoskins Susan , Lewis Kate Marie , Geismar Cyril , Navaratnam Annalan M D , Braithwaite Isobel , Byrne Thomas E , Oskrochi Youssof , Tweed Sam , Kovar Jana , Patel Parth , Hayward Andrew C , Aldridge Robert W 
Published: December 2022

AbstractBackgroundMigrants are over-represented in severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infections globally; however, evidence is limited for migrants in England and Wales. Household overcrowding is a risk factor for SARS-CoV-2 infection, with migrants more likely to live in overcrowded households than UK-born individuals. We aimed to estimate the total effect of migration status on SARS-CoV-2 infection and to what extent household overcrowding mediated this effect.MethodsWe included a sub-cohort of individuals from the Virus Watch prospective cohort study during the second SARS-CoV-2 wave (1st September 2020–30th April 2021) who were aged ≥18 years, self-reported the number of rooms in their household and had no evidence of SARS-CoV-2 infection pre-September 2020. We estimated total, indirect and direct effects using Buis’ logistic decomposition regression controlling for age, sex, ethnicity, clinical vulnerability, occupation, income and whether they lived with children.ResultsIn total, 23,478 individuals were included. 9.07% (187/2,062) of migrants had evidence of infection during the study period versus 6.27% (1,342/21,416) of UK-born individuals. Migrants had 22% higher odds of infection during the second wave (total effect; OR:1.22, 95%CI:1.01–1.47). Household overcrowding accounted for approximately 32% of these increased odds (indirect effect, OR:1.07, 95%CI:1.03–1.12; proportion accounted for: indirect effect[7]/total effect[22]=0.32).ConclusionMigrants had higher odds of SARS-CoV-2 infection during the second wave compared with UK-born individuals and household overcrowding explained 32% of these increased odds. Policy interventions to reduce household overcrowding for migrants are needed as part of efforts to tackle health inequalities during the pandemic and beyond.Key messagesWhat is already known on this topicMigrants in England and Wales may be at greater risk of exposure to SARS-CoV-2 due to unique risk factors, including over-representation in front-line jobs, an increased likelihood of living in multigenerational households and difficulties in accessing primary care. Research shows that migrants in high-income countries have been disproportionally infected with SARS-CoV-2. It is likely that, due to their pre-existing vulnerabilities, this is similarly the case for migrants in England and Wales; however, quantitative evidence addressing this is lacking.What this study addsWe investigated the effect of being a migrant on SARS-CoV-2 infection during the second wave of the pandemic in a cohort in England and Wales. We also determined the proportion of the effect mediated by household overcrowding after controlling for age, sex, ethnicity, clinical vulnerability, occupation, income and the presence of children in the household. Migrants had 22% higher odds of being infected with SARS-CoV-2 than their UK-born counterparts, and household overcrowding accounted for approximately 32% of these increased odds.How this study might affect research, practice or policyOur findings highlight the role of household overcrowding in the disproportionate impact of SARS-CoV-2 infections on migrants. They also demonstrate the urgent need for policy interventions that improve housing conditions as part of efforts to reduce health inequalities. Further research investigating other causes of migrants’ over-representation in infection cases is also needed to inform further targeted policy interventions.