Household Transmission of SARS-CoV-2: A Prospective Longitudinal Study Showing Higher Viral Load and Increased Transmissibility of the Alpha Variant Compared to Previous Strains
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Abstract
We studied the secondary attack rate (SAR), risk factors, and precautionary practices of household transmission in a prospective, longitudinal study. We further compared transmission between the Alpha (B.1.1.7) variant and non-Variant of Concern (non-VOC) viruses. From May 2020 throughout April 2021, we recruited 70 confirmed COVID-19 cases with 146 household contacts. Participants donated biological samples eight times over 6 weeks and answered questionnaires. SARS-CoV-2 infection was detected by real-time RT-PCR. Whole genome sequencing and droplet digital PCR were used to establish virus variant and viral load. SARS-CoV-2 transmission occurred in 60% of the households, and the overall SAR for household contacts was 50%. The SAR was significantly higher for the Alpha variant (78%) compared with non-VOC viruses (43%) and was associated with a higher viral load. SAR was higher in household contacts aged ≥40 years (69%) than in younger contacts (40–47%), and for contacts of primary cases with loss of taste/smell. Children had lower viral loads and were more often asymptomatic than adults. Sleeping separately from the primary case reduced the risk of transmission. In conclusion, we found substantial household transmission, particularly for the Alpha variant. Precautionary practices seem to reduce SAR, but preventing household transmission may become difficult with more contagious variants, depending on vaccine use and effectiveness.
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SciScore for 10.1101/2021.08.15.21261478: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Ethics Consent: Households willing to participate were visited at home, and written informed consent was obtained from the participants and/or their guardians before study inclusion.
IRB: The study was approved by the Regional Ethics Committee in Norway (#118354).Sex as a biological variable not detected. Randomization To account for dependencies within households, a mixed-effect logistic regression model with a household-level random intercept was used to study the associations between potential risk factors for transmission and of infection among the household contacts. Blinding not detected. Power Analysis not detected. Table 2: Resources
Software and Algorithms Sentences Resources All analyses were … SciScore for 10.1101/2021.08.15.21261478: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Ethics Consent: Households willing to participate were visited at home, and written informed consent was obtained from the participants and/or their guardians before study inclusion.
IRB: The study was approved by the Regional Ethics Committee in Norway (#118354).Sex as a biological variable not detected. Randomization To account for dependencies within households, a mixed-effect logistic regression model with a household-level random intercept was used to study the associations between potential risk factors for transmission and of infection among the household contacts. Blinding not detected. Power Analysis not detected. Table 2: Resources
Software and Algorithms Sentences Resources All analyses were performed in STATA/SE 15.0 (StataCorp. StataCorpsuggested: (Stata, RRID:SCR_012763)Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).
Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:The present study has several limitations. First, we did not design the study to evaluate differences in SAR between the Alpha variant and other non-VOC variants. Thus, the data presented regarding this difference is observational, as the dominance of the variants differed during the study period. We can therefore not exclude that climate, people’s behavior, or other factors, could have influenced our results. Quarantine and isolation guidelines were similar throughout the whole study period, thus we assume that this has not significantly influenced our results. Second, our sample size was small, which complicated the comparison between factors associated with the Alpha variant and other variants. Third, the age span of participants was limited, with few elderly individuals and mostly adult primary cases, although this may reflect the demographics in the study area. In conclusion, in this prospective longitudinal household study, we found an overall secondary attack rate for household contacts of 49.6%. The SAR was even higher for the Alpha variant, indicating a very high level of household transmission for this VOC. Implementation of precautionary measures in households after SARS-CoV-2 has been detected seem to reduce household transmission, but with more transmissible variants emerging, preventing transmission within a household will become increasingly difficult. Our results emphasize the role of households in the transmission of SARS-CoV-2 in the Norwegian population and...
Results from TrialIdentifier: No clinical trial numbers were referenced.
Results from Barzooka: We did not find any issues relating to the usage of bar graphs.
Results from JetFighter: We did not find any issues relating to colormaps.
Results from rtransparent:- Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
- Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
- No protocol registration statement was detected.
Results from scite Reference Check: We found no unreliable references.
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