Household transmission of SARS-CoV-2 Omicron variant of concern subvariants BA.1 and BA.2 in Denmark
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Abstract
SARS coronavirus 2 (SARS-CoV-2) continues to evolve and new variants emerge. Using nationwide Danish data, we estimate the transmission dynamics of SARS-CoV-2 Omicron subvariants BA.1 and BA.2 within households. Among 22,678 primary cases, we identified 17,319 secondary infections among 50,588 household contacts during a 1–7 day follow-up. The secondary attack rate (SAR) was 29% and 39% in households infected with Omicron BA.1 and BA.2, respectively. BA.2 was associated with increased susceptibility of infection for unvaccinated household contacts (Odds Ratio (OR) 1.99; 95%–CI 1.72-2.31), fully vaccinated contacts (OR 2.26; 95%–CI 1.95–2.62) and booster-vaccinated contacts (OR 2.65; 95%–CI 2.29–3.08), compared to BA.1. We also found increased infectiousness from unvaccinated primary cases infected with BA.2 compared to BA.1 (OR 2.47; 95%–CI 2.15–2.84), but not for fully vaccinated (OR 0.66; 95%–CI 0.57–0.78) or booster-vaccinated primary cases (OR 0.69; 95%–CI 0.59–0.82). Omicron BA.2 is inherently more transmissible than BA.1. Its immune-evasive properties also reduce the protective effect of vaccination against infection, but do not increase infectiousness of breakthrough infections from vaccinated individuals.
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Bernd Salzberger
Review 2: "Transmission of SARS-CoV-2 Omicron VOC subvariants BA.1 and BA.2: Evidence from Danish Households"
This preprint compares infectivity rates of the BA.1 and BA.2 COVID-19 subvariants within the fully vaccinated, boosted, and unvaccinated populations. Reviewers deem this study as strong and reliable with minor limitations in methodology and the transmissibility context.
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Marko Djordjevic
Review 1: "Transmission of SARS-CoV-2 Omicron VOC subvariants BA.1 and BA.2: Evidence from Danish Households"
This preprint compares infectivity rates of the BA.1 and BA.2 COVID-19 subvariants within the fully vaccinated, boosted, and unvaccinated populations. Reviewers deem this study as strong and reliable with minor limitations in methodology and the transmissibility context.
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Strength of evidence
Reviewers: Marko Djordjevic (University of Belgrade) | 📗📗📗📗◻️
Bernd Salzberger (University Hospital Regensburg) | 📘📘📘📘📘 -
SciScore for 10.1101/2022.01.28.22270044: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Ethics not detected. Sex as a biological variable not detected. Randomization not detected. Blinding not detected. Power Analysis not detected. Table 2: Resources
Software and Algorithms Sentences Resources A primary case was defined as the first individual in a household testing positive with an RT-PCR test within the study period and being identified with the Omicron VOC BA.1 or BA.2 by WGS. WGSsuggested: NoneResults 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:Some limitations apply to this …
SciScore for 10.1101/2022.01.28.22270044: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Ethics not detected. Sex as a biological variable not detected. Randomization not detected. Blinding not detected. Power Analysis not detected. Table 2: Resources
Software and Algorithms Sentences Resources A primary case was defined as the first individual in a household testing positive with an RT-PCR test within the study period and being identified with the Omicron VOC BA.1 or BA.2 by WGS. WGSsuggested: NoneResults 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:Some limitations apply to this study. The study period runs over Christmas 2021 and New Year’s Eve 2021/22, which are public holidays in Denmark. Despite government advice to limit social activity, it is likely that there has been considerable social mixing with family and friends outside the households during this period. Social mixing over the holidays in conjunction with the high incidence levels in Denmark during this period likely means that some secondary cases in this study are actually misclassified co-primary cases, i.e. infections picked up outside the household and testing positive after each other. However, this potential bias would be applicable to both subvariants. Moreover, our estimates were robust when only including primary cases from 5-11 January 2022 (appendix Table 12, model II) and when only including secondary cases found on day 2-7 or 3-7 (appendix Table 13, model VII and VIII). The present household study showed a transmission advantage of Omicron BA.2 over BA.1. Although vaccinations, in particular booster vaccinations, did protect against infection, the 2.45 (fully vaccinated) and 2.99 (booster vaccinated) fold higher odds of infection in BA.2 households indicate that BA.2 as a phenotype represents a further step in immune evasion in the Omicron lineage. However, it is likely that this change came with an evolutionary cost for BA.2. To our surprise, we found a decreased transmissibility of BA.2 relative to BA.1 among fully vaccinated and booster vac...
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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