Covid19-Sources

Table 4. Infection risk probability [%] results for any one individual in a group of 20 people (with and without universal FFP2 masking) after 8 hours of exposure on the coldest day (12th of January, left) and the warmest day (30th of June, right) of the academic year.ScenariosCold day risk (12th January) [%]Warm day risk (30th June) [%]Without masksWith masksWithout masksWith masks1. BC10027100272. MPIC-MEV 10 ℓ/s(p)4744743. MPIC-MEV 20 ℓ/s(p)3023024. AHU-HRV 10 ℓ/s(p)5755755. AHU-HRV 20 ℓ/s(p)3733836. NV-T4237277. NV-P595595 As might be expected, the results (Table 4) show the highest risk of infection occurs in scenario 1 as there is no active ventilation.

SARS-CoV-2 induces long-term alterations in Mac phenotypeTo explore long-term SARS-CoV-2 effects on innate immunity, we infected 25 cynomolgus macaques with wild-type (hereafter WTM, n = 15), Omicron BA.1 (n = 6) and Omicron BA.2 (n = 4) variants (hereafter OM), along with six noninfected macaques as controls (HC; Fig. 1a and Extended Data Table 1). Viral RNA loads peaked in nasal and tracheal swabs at day 3 postinfection (p.i.) in WTM and OM (7.9 × 108 and 2.78 × 107 copies per ml, respectively; Fig. 1a). Viral RNA was higher in the nasal swabs from WTM than OM (Extended Data Fig. 1a). By day 21, all macaques tested negative for SARS-CoV-2 RNA in nasal and tracheal swabs and remained negative by this readout up to 18 months p.i. (Fig. 1a). Immune responses were assessed at a median of 221 d p.i, with the analysis potentially extending to day 479 (Supplementary Table 1). Plasma immunoglobulin G (IgG) and IgA reactivities against spike and receptor-binding domain (RBD) were comparable in WTM and OM (Fig. 1b and Extended Data Fig. 1b). Inflammatory cytokines (interleukin (IL)-6, IL-18, IL-23, CXCL10) were higher in WTM and OM at 221 d.p.i. compared to HC (Extended Data Fig. 1c), suggesting lasting inflammation.

Overall seroprevalence was 53% (95% confidence interval (CI) 48–58%) among household contacts. The estimated household secondary attack rate is 34% (95% CI 5–75%). Mask wearing by the index case is associated with the household transmission risk reduction by 67% (adjusted odds ratio = 0.33 with 95% CI: 0.09–0.75) and not sharing bedroom with the index case is associated with the risk reduction of household transmission by 78% (adjusted odds ratio = 0.22 with 95% CI 0.10–0.41). The estimated distribution of household secondary attack rates is highly heterogeneous across index cases, with 30% of index cases being the source for 80% of secondary cases.

Conclusion Overall, prior infection was associated with a significant slightly elevated risk of severe disease. This effect varied month to month. As the pandemic proceeded, the effect of prior infection tended to evolve from generally protective during the pre-Omicron era to unprotective during the Omicron era. This points to the need for continued strategies to avert and minimize the harms of COVID-19, rather than relying upon immunity acquired through previous infection.