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1.
Preprint en Inglés | medRxiv | ID: ppmedrxiv-22276824

RESUMEN

BackgroundWe estimated the protection against the Omicron BA.2 variant associated with prior primary infection (PI) due to pre-Omicron or Omicron BA.1 virus, with and without mRNA vaccination. MethodsA test-negative case-control study was conducted among healthcare workers (HCWs) tested for SARS-CoV-2 in Quebec, Canada, between March 27 and June 4, 2022, when BA.2 predominated and was presumptively diagnosed. Logistic regression models compared the likelihood of BA.2 reinfection (second positive test [≥]30 days after PI) among HCWs with history of PI and none to three doses of mRNA vaccine versus infection-naive, unvaccinated HCWs. FindingsAmong 37,732 presumed BA.2 cases, 2,521 (6.7%) and 659 (1.7%) were reinfections following pre-Omicron or BA.1 PI, respectively. Among 73,507 controls, 7,360 (10.0%) and 12,315 (16.8%) had a pre-Omicron or BA.1 PI, respectively. Pre-Omicron PI was associated with 38% (95%CI:19-53) reduction in BA.2 infection risk, with higher BA.2 protection among those also vaccinated with one (56%), two (69%) or three (70%) vaccine doses. Omicron BA.1 PI was associated with greater protection against BA.2 (72%; 95%CI:65-78), higher among two-dose vaccinated at 96% (95%CI:95-96) but not improved with a third dose (96%; 95%CI:95-97). Hybrid Omicron BA.1 PI plus two or three dose vaccine-induced protection persisted for five months post-infection. InterpretationTwice-vaccinated individuals who experienced BA.1 infection were subsequently well-protected for a prolonged period against BA.2 reinfection and derived no meaningful added benefit against BA.2 from a third dose of mRNA vaccine.

2.
Preprint en Inglés | medRxiv | ID: ppmedrxiv-22274455

RESUMEN

ImportanceOmicron is phylogenetically- and antigenically-distinct from earlier SARS-CoV-2 variants and the original vaccine strain. Protection conferred by prior SARS-CoV-2 infection against Omicron re-infection, and the added value of vaccination, require quantification. ObjectiveTo estimate protection against Omicron re-infection and hospitalization conferred by prior heterologous SARS-CoV-2 (non-Omicron) infection and/or up to three doses of (ancestral, Wuhan-like) mRNA vaccine. DesignTest-negative study between December 26 (epi-week 52), 2021 and March 12 (epi-week 10), 2022. SettingPopulation-based, province of Quebec, Canada ParticipantsCommunity-dwelling [≥]12-year-olds tested for SARS-CoV-2. ExposuresPrior laboratory-confirmed infection with/without mRNA vaccination. OutcomesLaboratory-confirmed SARS-CoV-2 re-infection and hospitalization, presumed Omicron by genomic surveillance. The odds of prior non-Omicron infection with/without vaccination were compared among Omicron cases/hospitalizations versus test-negative controls (single randomly-selected per individual). Adjusted odds ratios controlled for age, sex, testing-indication and epi-week. Analyses were stratified by severity and time since last non-Omicron infection or vaccine dose. ResultsWithout vaccination, prior non-Omicron infection reduced the Omicron re-infection risk by 44% (95%CI:38-48), decreasing from 66% (95%CI:57-73) at 3-5 months to 35% (95%CI:21-47) at 9-11 months post-infection and <30% thereafter. The more severe the prior infection, the greater the risk reduction: 8% (95%CI:17-28), 43% (95%CI:37-49) and 68% (95%CI:51-80) for prior asymptomatic, symptomatic ambulatory or hospitalized infections. mRNA vaccine effectiveness against Omicron infection was consistently significantly higher among previously-infected vs. non-infected individuals at 65% (95%CI:63-67) vs. 20% (95%CI:16-24) for one-dose; 68% (95%CI:67-70) vs. 42% (95%CI:41-44) for two doses; and 83% (95%CI:81-84) vs. 73% (95%CI:72-73) for three doses. Infection-induced protection against Omicron hospitalization was 81% (95%CI: 66-89) increasing to 86% (95%CI:77-99) with one, 94% (95%CI:91-96) with two and 97%(95%CI:94-99) with three mRNA vaccine doses. Two-dose effectiveness against hospitalization among previously-infected individuals did not wane across 11 months and did not significantly differ from three-dose effectiveness despite longer follow-up (median 158 and 27 days, respectively). Conclusions and relevancePrior heterologous SARS-CoV-2 infection provided substantial and sustained protection against Omicron hospitalization, greatest among those also vaccinated. In the context of program goals to prevent severe outcomes and preserve healthcare system capacity, >2 doses of ancestral Wuhan-like vaccine may be of marginal incremental value to previously-infected individuals.

3.
Preprint en Inglés | medRxiv | ID: ppmedrxiv-22272057

RESUMEN

ImportanceMost adults with COVID-19 do not require hospitalization, but the subsequent risk of post-COVID condition, including associated psychological and cognitive dysfunction, remains poorly understood among non-hospitalized versus hospitalized cases. ObjectiveTo assess the prevalence and duration of post-COVID condition, including physical, psychological and cognitive symptoms. DesignCase series and case-control study between December 2020 and May 2021 SettingHealthcare workers in Quebec, Canada ParticipantsEligible cases were symptomatic healthcare workers with PCR-confirmed COVID-19 between July 2020 and May 2021. Among 17,717 contacted cases, 6061 (34%) participated. A random sample of symptomatic healthcare workers with negative PCR result between November 2020 and May 2021 served as controls. Among 11,498 contacted controls, 4390 (38%) participated. ExposuresIn multivariable models, sociodemographic and clinical characteristics, as well as vaccine history, were evaluated as potential risk factors. Prevalence ratios compared self-reported cognitive dysfunctions (difficulty concentrating; difficulty organizing oneself; forgetfulness; loss of necessary items) among cases with post-COVID condition to controls, adjusting for psychological distress and fatigue. OutcomesPost-COVID condition was defined by symptoms persisting [≥]4 weeks or [≥]12 weeks after COVID-19 onset. ResultsFour-week and 12-week post-COVID condition prevalences of 46% (2,746/5,943) and 40% (653/1,746), respectively, were observed among non-hospitalized cases and 76% (90/118) and 68% (27/37), respectively, among hospitalized cases. Hospitalization, female sex and age were associated with higher risk. A substantial proportion of non-hospitalized cases with 4-week post-COVID condition often or very often reported cognitive dysfunction, including concentration (33%) or organizing (23%) difficulties, forgetfulness (20%) and loss of necessary items (10%), with no decline at 12 weeks. All four aspects of cognitive dysfunction were 2.2 to 3.0 times more prevalent among cases with post-COVID condition than in controls, but also independently associated with psychological distress and fatigue. Conclusions and relevancePost-COVID condition may be a frequent sequela of ambulatory COVID-19 in working-age adults, with important effects on cognition. With so many healthcare workers infected since the beginning of the COVID-19 pandemic, the ongoing implications for quality healthcare delivery could be profound should cognitive dysfunction and other severe post-COVID symptoms persist in a professionally-disabling way over the longer term. Key pointsO_ST_ABSQuestionC_ST_ABSHow common and long-lasting are the physical, psychological and cognitive effects of post-COVID condition in healthcare workers, both hospitalized and non-hospitalized? FindingsThe prevalence of post-COVID condition was 46% at 4 weeks and 40% at 12 weeks among non-hospitalized cases and 76% and 68% among hospitalized cases. One third of non-hospitalized healthcare workers with post-COVID condition reported cognitive impairment, which was independently associated with persistent physical symptoms, but also psychological distress and fatigue. MeaningPersistent cognitive and other professionally-disabling sequelae of COVID-19 in essential workers could have critical implications for quality healthcare delivery during and after the pandemic.

4.
Preprint en Inglés | medRxiv | ID: ppmedrxiv-21265397

RESUMEN

BackgroundThe Canadian COVID-19 immunization strategy deferred second doses and allowed mixed schedules. We compared two-dose vaccine effectiveness (VE) by vaccine type (mRNA and/or ChAdOx1), interval between doses, and time since second dose in two of Canadas larger provinces. MethodsTwo-dose VE against infections and hospitalizations due to SARS-CoV-2, including variants of concern, was assessed between May 30 and October 2, 2021 using test-negative designs separately conducted among community-dwelling adults [≥]18-years-old in British Columbia (BC) and Quebec, Canada. FindingsIn both provinces, two doses of homologous or heterologous SARS-CoV-2 vaccines were associated with [~]95% reduction in the risk of hospitalization. VE exceeded 90% against SARS-CoV-2 infection when at least one dose was an mRNA vaccine, but was lower at [~]70% when both doses were ChAdOx1. Estimates were similar by age group (including adults [≥]70-years-old) and for Delta-variant outcomes. VE was significantly higher against both infection and hospitalization with longer 7-8-week vs. manufacturer-specified 3-4-week interval between doses. Two-dose mRNA VE was maintained against hospitalization for the 5-7-month monitoring period and while showing some decline against infection, remained [≥]80%. InterpretationTwo doses of mRNA and/or ChAdOx1 vaccines gave excellent protection against hospitalization, with no sign of decline by 5-7 months post-vaccination. A 7-8-week interval between doses improved VE and may be optimal in most circumstances. Findings indicate prolonged two-dose protection and support the use of mixed schedules and longer intervals between doses, with global health, equity and access implications in the context of recent third-dose proposals.

5.
Preprint en Inglés | medRxiv | ID: ppmedrxiv-21265175

RESUMEN

ObjectiveWe aimed to measure the prevalence of psychological distress among Quebec healthcare workers (HCWs) during the second and third pandemic waves and to assess the effect of psychosocial risk factors (PSRs) on work-related psychological distress among SARS-CoV-2 infected (cases) and non-infected (controls) HCWs. MethodsA self-administered survey was used to measure validated indicators of psychological distress (K6 scale) and PSR (questions based on Karasek and Siegrist models, value conflicts and work-life balance). Adjusted robust Poisson models were used to estimate prevalence ratios. Results4068 cases and 4152 controls completed the survey. Prevalence of high work-related psychological distress was 42%; it was associated with PSRs (mainly work-life balance, value conflicts and high psychological demands) but not with SARS-CoV-2 infection. ConclusionPrimary prevention measures targeting PSRs are needed to reduce mental health risks of HCWs.

6.
Preprint en Inglés | medRxiv | ID: ppmedrxiv-21260445

RESUMEN

IntroductionIn Canada, first and second doses of mRNA vaccines against SARS-CoV-2 were uniquely spaced 16 weeks apart, but the duration of single-dose protection remains uncertain. We estimated one- and two-dose mRNA vaccine effectiveness (VE) among healthcare workers (HCWs) in Quebec, Canada including protection against varying outcome severity, variants of concern (VOC), and the stability of single-dose protection out to 16 weeks post-vaccination. MethodsA test-negative design compared vaccination among SARS-CoV-2 test-positive and weekly-matched (10:1), randomly-sampled, test-negative HCWs using linked surveillance and immunization databases. Vaccine status was defined by one dose [≥]14 days or two doses [≥]7 days before illness onset or specimen collection. Adjusted VE was estimated by conditional logistic regression. ResultsPrimary analysis included 5,316 cases and 53,160 controls. Single-dose VE was 70% (95%CI: 68-73) against SARS-CoV-2 infection, 73% (95%CI: 71-75) against COVID-19 illness and 97% (95%CI: 92-99) against associated hospitalization. Two-dose VE was 86% (95%CI: 81-90) and 93% (95%CI: 89-95), respectively, with no associated hospitalizations. VE was higher for non-VOC than VOC (73% Alpha) among single-dose (77%, 95%CI: 73-81 versus 63%, 95%CI: 57-67) but not two-dose recipients (87%, 95%CI: 57-96 versus 94%, 95%CI: 89-96). Across 16 weeks, no decline in single-dose VE was observed with appropriate stratification based upon prioritized vaccination determined by higher versus lower likelihood of direct patient contact. ConclusionOne mRNA vaccine dose provided substantial and sustained protection to HCWs extending at least four months post-vaccination. In circumstances of vaccine shortage, delaying the second dose may be a pertinent public health strategy to consider.

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