Increased household transmission and immune escape of the SARS-CoV-2 Omicron compared to Delta variants

  1. Neda Jalali
  2. Hilde K. Brustad
  3. Arnoldo Frigessi
  4. Emily A. MacDonald
  5. Hinta Meijerink
  6. Siri L. Feruglio
  7. Karin M. Nygård
  8. Gunnar Rø
  9. Elisabeth H. Madslien
  10. Birgitte Freiesleben de Blasio

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Abstract

Understanding the epidemic growth of the novel SARS-CoV-2 Omicron variant is critical for public health. We compared the ten-day secondary attack rate (SAR) of the Omicron and Delta variants in households using Norwegian contact tracing data, December 2021 - January 2022. Omicron SAR was higher than Delta, with a relative risk (RR) of 1.41 (95% CI 1.27-1.56). We observed increased susceptibility to Omicron infection in household contacts compared to Delta, independent of contacts’ vaccination status. Among three-dose vaccinated contacts, the mean SAR was lower for both variants. We found increased Omicron transmissibility from primary cases to contacts in all vaccination groups, except 1-dose vaccinated, compared to Delta. Omicron SAR of three-dose vaccinated primary cases was high, 46% vs 11 % for Delta. In conclusion, three-dose vaccinated primary cases with Omicron infection can efficiently spread in households, while three-dose vaccinated contacts have a lower risk of being infected by Delta and Omicron.

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  1. Version published to 10.1038/s41467-022-33233-9
  2. Version published to 10.21203/rs.3.rs-1370541/v1 on Research Square
  3. ScreenIT

    SciScore for 10.1101/2022.02.07.22270437: (What is this?)

    Please note, not all rigor criteria are appropriate for all manuscripts.

    Table 1: Rigor

    Ethicsnot detected.
    Sex as a biological variablenot detected.
    Randomizationnot detected.
    Blindingnot detected.
    Power Analysisnot detected.

    Table 2: Resources

    Software and Algorithms
    SentencesResources
    Statistical analyses were performed with Rstudio 1.3.1056.
    Rstudio
    suggested: (RStudio, RRID:SCR_000432)

    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 SAR estimates were generally higher in our study, which could be due to various reasons such as differences in the testing regimes or discrepancies in the capacity and procedures for registering household contacts; see Supplementary S4 for study limitations. In this study, we have used contact tracing data, and this may give higher estimates of SAR than registry-based studies, since the exposure is identified through personal interviews. Furthermore, since the included children <16 years were mostly unvaccinated or partially vaccinated, this could contribute to the overall higher household SAR for both Delta and Omicron observed in our study. The overall difference in SAR between the strains was surprisingly small, given the rapid takeover of Omicron from Delta in Norway. This finding may be due to the study setting, as household exposure is often prolonged and repeated. Unfortunately, inclusion of non-household contacts was not possible due to variations in contact tracing practices during the study period and between localities. Similar to Lyngse et al., we found no significant difference in the SAR in households with Omicron and Delta among unvaccinated or partially vaccinated, suggesting that intrinsic transmissibility is not particularly higher in the Omicron variant compared to Delta. This finding contradicts early assumptions that the Omicron is fundamentally more transmissible than Delta [15]. As expected, vaccination with two and three doss seemed to give lower p...

    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.

    About SciScore

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  4. Version published to 10.1101/2022.02.07.22270437 on medRxiv