Abstract
Historically SARS-CoV-2 secondary attack rates (SAR) have been based on PCR positivity on screening symptomatic contacts, this misses transmission events and identifies only symptomatic contacts who are PCR positive at the time of sampling. We used serology to detect the relative transmissibility of Alpha Variant of Concern (VOC) to non-VOC SARS-CoV-2 to calculate household secondary attack rates. We identified index patients diagnosed with Alpha and non-VOC SARS-CoV-2 across two London Hospitals between November 2020 and January 2021 during a prolonged and well adhered national lockdown. We completed a household seroprevalence survey and found that 61.8% of non-VOC exposed household contacts were seropositive compared to 82.1% of Alpha exposed household contacts. The odds of infection doubled with exposure to an index diagnosed with Alpha. There was evidence of transmission events in almost all households. Our data strongly support that estimates of SAR should include serological data to improve accuracy and understanding.
Key Messages Secondary attack rates (SAR) in SARS-CoV-2 were previously calculated using PCR positive samples only, it is more accurate to use a household transmission model and screen contacts using serology, as done in this study. SAR should include serological data to improve accuracy and understanding. All households in this study had transmission events. SAR were 61.8% in non-VOC SARS-CoV-2 exposed household contacts compared to 82.1% in Alpha SARS-CoV-2 exposed household contacts.
Competing Interest Statement
The authors have declared no competing interest.
Funding Statement
This research was funded by the LSHTM COVID-19 response fund Grant number DONAT15914 and performed independently to any intervention by this funder.
Author Declarations
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The details of the IRB/oversight body that provided approval or exemption for the research described are given below:
The ethics committees of LSHTM (LEO ref:25265), the NHS Health Research authority (IRAS ref:295376), and local hospital review committees gave full ethical approval for this work.
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Data Availability
All anonymised data produced in the present study are available upon reasonable request to the authors