RESUMO
BackgroundWe evaluated measures to protect healthcare workers (HCWs) in Vancouver, Canada, where variants of concern (VOC) went from <1% in February 2021 to >92% in mid-May. Canada has amongst the longest periods between vaccine doses worldwide, despite Vancouver having the highest P.1 variant rate outside Brazil. MethodsWith surveillance data since the pandemic began, we tracked laboratory-confirmed SARS-CoV-2 infections, positivity rates, and vaccine uptake in all 25,558 HCWs in Vancouver Coastal Health, by occupation and subsector, and compared to the general population. We employed Cox regression modelling adjusted for age and calendar-time to calculate vaccine effectiveness (VE) against SARS-CoV-2 in fully vaccinated ([≥] 7 days post-second dose), partially vaccinated (14 days post vaccine) and unvaccinated HCWs; we also compared with unvaccinated community members of the same age-range. FindingsOnly 3.3% of our HCWs became infected, mirroring community rates, with peak positivity of 9.1%, compared to 11.8% in the community. As vaccine coverage increased, SARS-CoV-2 infections declined significantly in HCWs, despite a surge with predominantly VOC; unvaccinated HCWs had an infection rate of 1.3/10,000 person-days compared to 0.89 for HCWs post first dose, and 0.30 for fully vaccinated HCWs. VE compared to unvaccinated HCWs was 37.2% (95% CI: 16.6-52.7%) 14 days post-first dose, 79.2% (CI: 64.6-87.8%) 7 days post-second dose; one dose provided significant protection against infection until at least day 42. Compared with community infection rates, VE after one dose was 54.7% (CI: 44.8-62.9%); and 84.8% (CI: 75.2-90.7%) when fully vaccinated. InterpretationPredominantly droplet-contact precautions, with N95s required for aerosol generating medical procedures and available as needed according to point-of-care risk assessment, has been a highly effective approach to preventing occupational infection in HCWs, with one dose of mRNA vaccination further reducing infection risk despite VOC and transmissibility concerns. Delaying second doses to allow more widespread vaccination against severe disease, with strict public health, occupational health and infection control measures, has been effective in protecting the healthcare workforce.
RESUMO
BackgroundThe aim of this prospective cohort study was to determine the burden of SARS-CoV-2 in air and on surfaces in rooms of patients hospitalized with COVID-19, and to identify patient characteristics associated with SARS-CoV-2 environmental contamination. MethodsNasopharyngeal swabs, surface, and air samples were collected from the rooms of 78 inpatients with COVID-19 at six acute care hospitals in Toronto from March to May 2020. Samples were tested for SARS-CoV-2 viral RNA and cultured to determine potential infectivity. Whole viral genomes were sequenced from nasopharyngeal and surface samples. Association between patient factors and detection of SARS-CoV-2 RNA in surface samples were investigated using a mixed-effects logistic regression model. FindingsSARS-CoV-2 RNA was detected from surfaces (125/474 samples; 42/78 patients) and air (3/146 samples; 3/45 patients) in COVID-19 patient rooms; 17% (6/36) of surface samples from three patients yielded viable virus. Viral sequences from nasopharyngeal and surface samples clustered by patient. Multivariable analysis indicated hypoxia at admission, a PCR-positive nasopharyngeal swab with a cycle threshold of [≤]30 on or after surface sampling date, higher Charlson co-morbidity score, and shorter time from onset of illness to sample date were significantly associated with detection of SARS-CoV-2 RNA in surface samples. InterpretationThe infrequent recovery of infectious SARS-CoV-2 virus from the environment suggests that the risk to healthcare workers from air and near-patient surfaces in acute care hospital wards is likely limited. Surface contamination was greater when patients were earlier in their course of illness and in those with hypoxia, multiple co-morbidities, and higher SARS-CoV-2 RNA concentration in NP swabs. Our results suggest that air and surfaces may pose limited risk a few days after admission to acute care hospitals.