Transmission of SARS-CoV-2 into and within immigrant households. Nation-wide registry-study from Norway

Background: Minority ethnic groups and immigrants have been hit disproportionally hard by COVID-19 in many developed countries, including Norway. Most transmissions of SARS-CoV-2 occur in households. Methods: Using individual-level registry data of all Norwegian residents we compared infections across all multi-person households. A household with at least one member born abroad was defined as an immigrant household. For the subset of households where at least one person tested positive for SARS-CoV-2 from August 1st 2020 to May 1st 2021, we calculated secondary attack rates (SARs) as the percent of other household members testing positive within 14 days after the first household member tested positive. Logistic regression model was used to adjust for sex, age, household composition and geography. Results: Among all multi-person households in Norway (n=1 421 642), immigrant households (n=341 604) comprised more members on average (3.2) than households with only Norwegian-born members (2.8). The share of immigrant households where at least one member had been tested, was 56% (vs 49% in the households with only Norwegian-born members), and the share where at least one member was infected was 3.7% (vs 1.4% in households with only Norwegian-born members). Secondary attack rates were higher in immigrant (32%) than Norwegian-born households (20%). Results differed considerably by country of birth, with secondary attack rates particularly high in households from Syria, Iraq, Turkey, and Pakistan, also after adjustment for sex, age, household composition and geography. Conclusion: SARS-CoV-2 is more frequently introduced into multi-person immigrant households than into households with only Norwegian-born members, and transmission within the household occurs more frequently in immigrant households. The results are likely related to living conditions, family composition or differences in social interaction, emphasizing the need to prevent introduction of SARS-CoV-2 into these vulnerable households.