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Preprint: SARS-CoV-2 Omicron VOC Transmission in Danish Households

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  • Preprint: SARS-CoV-2 Omicron VOC Transmission in Danish Households

    Preprint: SARS-CoV-2 Omicron VOC Transmission in Danish Households

    Omicron's Record Surge - Credit Our World In Data


    Six weeks ago, nobody had ever heard of the Omicron variant, but in a little over a month it has become the dominant COVID strain in the United States, much of Europe, and threatens to conquer the world in early 2022.

    According to the New York Times, more than 580,000 cases were reported in the United States over the past 24 hours - more than doubling the heights reached during last winter's epidemic wave - and even this is likely an undercount.

    While there is some evidence to suggest that Omicron may be milder - at least in vaccinated individuals - the sheer volume of cases over the next few weeks threatens healthcare delivery systems (see Maryland: Multiple Hospitals Activate Crisis Standards of Care, and society in general.

    No matter how difficult things may get in the weeks ahead, we have to count ourselves lucky that the first wave of COVID in early 2020 - before anyone had any immunity - wasn't as aggressive as Omicron appears to be now.

    But immunity, either through previous infection or vaccination, against Omicron isn't as robust as we saw against Delta. Transmission of Omicron is remarkably high, even among those who are fully vaccinated, but there is evidence to suggest that vaccination still reduces your odds of infection.

    We've a new preprint, from researchers in Denmark, that attempts to quantify the effects of vaccination (including booster shots) on the household transmission of Omicron. First the SSI Summary, followed by a link and the abstract to the preprint.

    I'll have a brief postscript after the break.

    Vaccination protects against infection in households shows new study

    Researchers from the University of Copenhagen, Statistics Denmark, DTU and the Statens Serum Institut have investigated how much the omicron variant is contagious in relation to the delta variant in Danish households. The new study takes into account a number of factors including vaccination.
    Last edited December 31, 2021
    Ever since the omicron variant appeared in November, researchers have been working to find out how contagious it is compared to other covid-19 variants.

    Now comes a new Danish study with part of the answer. Researchers from the University of Copenhagen, Statistics Denmark, DTU and the Statens Serum Institut (SSI) have investigated how much the omicron variant is contagious in relation to the delta variant in Danish households.

    The results indicate that the rapid spread of the omicron variant is largely due to its ability to evade immunity built up by vaccination.

    Read the pre-print version of the new studio here.

    Higher infection among unvaccinated

    The study also looked at the effect of vaccination in relation to household infection. In general, there was a higher transmission for unvaccinated individuals and a lower transmission for booster-vaccinated individuals compared to fully vaccinated individuals. This applied regardless of the variant with which the household was infected.

    Transmission is here an overall estimate of transmission from an infected vaccinated and a vaccinated "recipient" of the infection.

    And higher infection in "omikron households"

    When comparing households infected with the omicron variant and households infected with the delta variant, there was a significantly higher transmission depending on vaccination status.

    11,937 households surveyed

    The study included 11,937 households (of which 2,225 with omicron infection) and 27,874 household members.

    A total of 6,397 household members were tested positive within 1-7 days after the first person in the household was tested positive. The calculated attack rate was 31% and 21% in omicron- and delta-variant-infected households, respectively.

    Read more

    The study has just been published as a working paper (not yet peer-reviewed) and is available on a pre-print server:

    SARS-CoV-2 Omicron VOC Transmission in Danish Households

    Frederik Plesner Lyngse, Laust Hvas Mortensen, Matthew J. Denwood, Lasse Engbo Christiansen, Camilla Holten Møller, VRobert Leo Skov,Katja Spiess, Anders Fomsgaard, Ria Lassauniere, Morten Rasmussen, ProfileMarc Stegger, Claus Nielsen, Raphael Niklaus Sieber, Arieh Sierra Cohen, Frederik Trier Møller, Maria Overvad, Kåre Mølbak, Tyra Grove Krause, Carsten Thure Kirkeby


    The Omicron variant of concern (VOC) is a rapidly spreading variant of SARS-CoV-2 that is likely to overtake the previously dominant Delta VOC in many countries by the end of 2021. We estimated the transmission dynamics following the spread of Omicron VOC within Danish households during December 2021.

    We used data from Danish registers to estimate the household secondary attack rate (SAR). Among 11,937 households (2,225 with the Omicron VOC), we identified 6,397 secondary infections during a 1-7 day follow-up period. The SAR was 31\% and 21\% in households with the Omicron and Delta VOC, respectively.

    We found an increased transmission for unvaccinated individuals, and a reduced transmission for booster-vaccinated individuals, compared to fully vaccinated individuals.

    Comparing households infected with the Omicron to Delta VOC, we found an 1.17 (95\%-CI: 0.99-1.38) times higher SAR for unvaccinated, 2.61 times (95\%-CI: 2.34-2.90) higher for fully vaccinated and 3.66 (95\%-CI: 2.65-5.05) times higher for booster-vaccinated individuals, demonstrating strong evidence of immune evasiveness of the Omicron VOC. Our findings confirm that the rapid spread of the Omicron VOC primarily can be ascribed to the immune evasiveness rather than an inherent increase in the basic transmissibility.

    (Continue . . . . )

    Due to the finding that transmission of Omicron was only marginally higher among the unvaccinated than it was Delta, these researchers suggest the rapid spread of Omicron is due mostly to reduced protection from prior immunity (via vaccines and/or previous infection) compared to the Delta variant.

    This does not say (as some on the internet will undoubtedly misconstrue), that the vaccinated are more likely to be infected, or to spread Omicron, than the unvaccinated.

    Instead the authors conclude:

    Our results show that the Omicron VOC is generally 2.7-3.7 times more infectious than the Delta VOC among vaccinated individuals (Table 3). This observation is in line with data from (18), which estimated that 19% of Omicron VOC primary cases in households in the UK resulted in at least one other infection within the household, compared to only 8.3% of those associated with the Delta VOC.

    Furthermore, we show that fully vaccinated and booster-vaccinated individuals are generally less susceptible to infection compared to unvaccinated individuals (Table 2). We also show that booster-vaccinated individuals generally had a reduced transmissibility (OR: 0.72, CI: 0.56-0.92), and that unvaccinated individuals had a higher transmissibility (OR: 1.41, CI: 1.27-1.57), compared to fully vaccinated individuals.

    (Continue . . . )

    While vaccination against COVID is no guarantee you won't catch, or pass on, Omicron - it does lower your odds of infection - and likely reduces your risk of experiencing severe illness, or death.

    Perhaps not as much as we had initially hoped from a COVID vaccine, but it is still far better than it might have been.
    All medical discussions are for educational purposes. I am not a doctor, just a retired paramedic. Nothing I post should be construed as specific medical advice. If you have a medical problem, see your physician.

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