In interim 2025/26 analyses, the Canadian Sentinel Practitioner Surveillance Network estimates influenza vaccine reduced the risk of medically-attended acute respiratory illness due to predominant influenza A(H3N2) viruses, including antigenically distinct subclade K, by about 40% relative to unvaccinated individuals. Vaccine effectiveness was about 30% against A(H1N1)pdm09, with insufficient case numbers for interim influenza B estimation. Meaningful protection against subclade K, despite substantial vaccine mismatch, is interpreted in the context of immuno-epidemiological considerations, including potential viral glycosylation, imprinting, and pre-immunity effects.

The Canadian Sentinel Practitioner Surveillance Network (SPSN) reports interim 2024/25 vaccine effectiveness (VE) against acute respiratory illness due to laboratory-confirmed influenza during a delayed season of predominant A(H1N1)pdm09 and lower A(H3N2) co-circulation. Through mid-January, the risk of outpatient illness due to influenza A is reduced by about half among vaccinated vs unvaccinated individuals. Adjusted VE is 53% (95% CI: 36-65) against A(H1N1) pdm09, comprised of clades 5a.2a and 5a.2a.1, and 54% (95% CI: 29-70) against A(H3N2), virtually all clade 2a.3a.1.

BackgroundTetanus and diphtheria (Td) antibody titers can be measured to assess for seroprotection from immunization, though this is not routinely indicated. There are limited population level data on the utilization of these tests and their results.MethodsThis is a population level retrospective study based on laboratory data collected from patients who underwent Td antibody testing. Td IgG titer requests from May 1, 2023, to December 31, 2024, were extracted from the provincial health information system of Alberta, Canada. Td anti-toxin test requests, geometric mean titers, and vaccination status of patients who underwent testing were analyzed. Individuals with multiple tests were assessed for changes in antibody levels, and the proportion of tested individuals who were vaccinated within the past 10 years was calculated. Geometric mean titers were interpreted in relation to established thresholds for long-term protective immunity.ResultsA total of 2,550 patients underwent testing for tetanus (n = 2,349) and diphtheria (n = 2,093) anti-toxin antibody levels. Geometric mean titers varied widely across physician specialties, with pediatrics and Immunology showing higher proportions of recent vaccinations and higher geometric mean titers, while general practice and nephrology had lower values. Nearly 40% of diphtheria test orders in patients immunized within the past 10 years were requested by general practice (n = 336). In contrast, less than 20% of tests were ordered by nephrology (n = 153), pediatrics (n = 95), and pharmacy (n = 12).ConclusionOver half the tests were requested by general practice. Our study highlighted variability in vaccination patterns and immune responses across specialties. While antibody testing is useful for assessing protection, a considerable number of tests were performed in individuals likely to be protected by recent vaccination, pointing to inefficiencies and unnecessary healthcare spending. These findings underscore the importance of aligning test ordering practices with immunization history to optimize resource use, avoid redundant testing, support diagnostic stewardship, and inform more cost-effective public health strategies.

ABSTRACT Introduction The COVID-19 pandemic demonstrated the need for comprehensive, cost-effective surveillance systems integrating multiple data streams. This study directly compares SARS-CoV-2 genomic data from wastewater-based surveillance (WBS) and clinical diagnostic testing (CDT) to evaluate lineage diversity, detection timing, and persistence patterns that could inform integrated surveillance strategies. Methods We analyzed SARS-CoV-2 genomic data from Alberta, Canada (July 2022 to March 2025), encompassing 13 municipal wastewater treatment plants covering 80% of the provincial population and clinical samples from provincial diagnostic testing. Clinical samples (n=28,610) and wastewater samples (n=1,685) were sequenced using a tiled amplicon approach. We compared lineage richness over time, lead time for first detection using collection dates and explored four additional wastewater metrics: abundance at first detection, peak abundance, time to peak abundance, and total time detected. The comparison grouped lineages into those found only in WBS and those that were seen in both WBS and CDT. Results Of the 2,586 unique lineages identified over the study period, 1,588 (61.1%) appeared exclusively in WBS, 42 (1.6%) only in CDT, and 956 (36.9%) in both systems. WBS consistently demonstrated higher monthly lineage richness (95-660 lineages) compared to CDT (23-160 lineages). While WBS detected lineages an average of almost 12 days earlier than CDT, the most frequent pattern showed CDT detection first by 8 days, indicating substantial variability. Lineages detected in both systems showed significantly higher initial relative abundance, peak relative abundance, longer persistence, and delayed time to peak compared to WBS-only lineages (all p<0.0001). Conclusions WBS and CDT provide complementary surveillance capabilities with distinct strengths. Rather than relying on first detection as an early warning metric, integrated surveillance should prioritize concordance patterns and abundance metrics that indicate lineages with sustainable transmission potential. These findings support developing surveillance frameworks that strategically combine population-level WBS monitoring with case-linked CDT data for more effective public health response. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This work was funded by the Public Health Agency of Canada Integral Genomics Innovation Grants and the Public Health Agency of Canada Wastewater Surveillance Fund. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: This study was reviewed and approved by the Conjoint Health Research Ethics Board at the University of Calgary (Ethics ID: REB21-0877_REN4). All consensus sequences from CDT are available through GISAID and the Canadian VirusSeq portal. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All clinical data in the present study are available through GISAID and the Canadian VirusSeq portal

Background:Solid organ transplant recipients with resolved hepatitis B virus (HBV) infection are at risk for reactivation; however, most of the studies have focused on kidney transplant recipients and have short to intermediate term follow-up. Risk factors for reactivation are also uncertain, with some studies suggesting surface antibody (anti-HBs) may be protective. Methods:This retrospective single-center study aimed to assess the risk of HBV reactivation (HBVr) in lung transplant recipients with prior HBV infection as well as the value of anti-HBs titers in predicting HBVr. Surface antigen (HBsAg) negative, core antibody (anti-hepatitis B core (HBc)) positive adult lung and heart-lung solid organ transplant recipients from 2005 to 2019 were included. The primary outcome was HBVr after transplant, defined as seroreversion to HBsAg positivity. The secondary outcome compared anti-HBs titers at transplant and at post-transplant month 12. Results:The cohort included 38 lung and heart-lung recipients with anti-HBc positive, HBsAg negative pretransplant serology. Reactivation occurred in 3 of 38 (8%) at 49, 69, and 94 months post transplant. Two (5% of cohort) subjects died as a consequence of HBVr. Two of the 3 HBVr patients had anti-HBs titers >10 IU/ml at transplant and 1 had anti-HBs >100 IU/ml at time of HBV reactivation. We did not find a statistically significant decrease in anti-HBs titers 1 year after transplant in subjects with baseline anti-HBs >10 IU/ml. Conclusions:The prolonged time to reactivation highlights the lifelong risk. The 8% rate of reactivation and 5% mortality support a preferred strategy of indefinite HBV antiviral prophylaxis over monitoring in anti-HBc positive lung recipients.

BACKGROUND:The unprecedented COVID-19 pandemic has highlighted the strategic value of wastewater-based surveillance (WBS) of SARS-CoV-2. This multisite 28-month-long study focused on WBS for older residents in 12 long-term care facilities (LTCFs) in Edmonton (AB, Canada) by assessing relationships between COVID-19, WBS, and serostatus during the pandemic. METHODS:Wastewater samples collected two to three times per week were tested for SARS-CoV-2 using RT-quantitative PCR. The serostatus of antibodies was examined using immunoassays. The data of clinical COVID-19 outbreaks based on extensive testing were obtained from local public health officials. Analyses included calculating correlations between 7-day rolling averages for WBS and COVID-19 cases and investigating whether WBS led or lagged confirmed outbreaks using a multinomial test. FINDINGS:Wastewater results correlated well with clinical COVID-19 infections and outbreaks at participating LTCFs. 1058 (36·0%) of 2936 collected wastewater samples were SARS-CoV-2 positive, compared with 1247 people (resident n=671, staff n=572, and unknown n=4) reporting positive test results of 21 673 clinical samples assessed (5·8%). WBS led clinical testing in 32 (60·4%) confirmed outbreaks, which was significantly different from WBS lagged (12 outbreaks [22·6%, 95% CI 11·3-33·7]). Non-detection of WBS SARS-CoV-2 served as a negative predictor for outbreaks. WBS results attested protective immunity in vaccinated individuals before the omicron wave. A parallel increase in the proportions of positive WBS SARS-CoV-2 and anti-nucleocapsid antibodies underlined that omicron was an immunity-evading variant despite high seropositivity of neutralising antibodies after multiple doses of vaccine. INTERPRETATION:Implementation of WBS could enable targeted clinical investigations and improve cost-effectiveness of COVID-19 outbreak management in LTCFs. WBS and serostatus provided informed dynamic changes of infections and immunity. Critical evidence was that LTCF WBS is an effective early warning system to support rapid public health outbreak management and protect vulnerable older populations. FUNDING:Canadian Immunity Task Force for COVID-19 and Alberta Health.

Timely and precise influenza vaccine effectiveness (VE) estimates are needed to guide public health messaging and impact vaccine uptake immediately. Using routinely collected laboratory, vaccination and health administrative data from Alberta, Canada, we estimated influenza VE against infection for the 2023/24 season on a near real-time basis, to late December, at 61% (95% CI: 58-64) against influenza A(H1N1), 49% (95% CI: 28-63) against influenza A(H3N2) and 75% (95% CI: 58-85) against influenza B.

The Canadian Sentinel Practitioner Surveillance Network reports mid-season 2023/24 influenza vaccine effectiveness (VE) of 63% (95% CI: 51–72) against influenza A(H1N1)pdm09, lower for clade 5a.2a.1 (56%; 95% CI: 33–71) than clade 5a.2a (67%; 95% CI: 48–80), and lowest against influenza A(H3N2) (40%; 95% CI: 5–61). The Omicron XBB.1.5 vaccine protected comparably well, with VE of 47% (95% CI: 21–65) against medically attended COVID-19, higher among people reporting a prior confirmed SARS-CoV-2 infection at 67% (95% CI: 28–85).

Wastewater-based surveillance is a valuable approach for monitoring COVID-19 at community level. Monitoring SARS-CoV-2 variants of concern (VOC) in wastewater has become increasingly relevant when clinical testing capacity and case-based surveillance are limited. In this study, we ascertained the turnover of six VOC in Alberta wastewater from May 2020 to May 2022. Wastewater samples from nine wastewater treatment plants across Alberta were analysed using VOC-specific RT-qPCR assays. The performance of the RT-qPCR assays in identifying VOC in wastewater was evaluated against next generation sequencing. The relative abundance of each VOC in wastewater was compared to positivity rate in COVID-19 testing. VOC-specific RT-qPCR assays performed comparatively well against next generation sequencing; concordance rates ranged from 89% to 98% for detection of Alpha, Beta, Gamma, Omicron BA.1 and Omicron BA.2, with a slightly lower rate of 85% for Delta (p < 0.01). Elevated relative abundance of Alpha, Delta, Omicron BA.1 and BA.2 were each associated with increased COVID-19 positivity rate. Alpha, Delta and Omicron BA.2 reached 90% relative abundance in wastewater within 80, 111 and 62 days after their initial detection, respectively. Omicron BA.1 increased more rapidly, reaching a 90% relative abundance in wastewater after 35 days. Our results from VOC surveillance in wastewater correspond with clinical observations that Omicron is the VOC with highest disease burden over the shortest period in Alberta to date. The findings suggest that changes in relative abundance of a VOC in wastewater can be used as a supplementary indicator to track and perhaps predict COVID-19 burden in a population.

The Canadian Sentinel Practitioner Surveillance Network estimated vaccine effectiveness (VE) during the unusually early 2022/23 influenza A(H3N2) epidemic. Like vaccine, circulating viruses were clade 3C.2a1b.2a.2, but with genetic diversity affecting haemagglutinin positions 135 and 156, and reassortment such that H156 viruses acquired neuraminidase from clade 3C.2a1b.1a. Vaccine provided substantial protection with A(H3N2) VE of 54% (95% CI: 38 to 66) overall. VE was similar against H156 and vaccine-like S156 viruses, but with potential variation based on diversity at position 135.

BACKGROUND:Randomized trials conducted in low- and middle-income settings demonstrated efficacy of influenza vaccination during pregnancy against influenza infection among infants <6 months of age. However, vaccine effectiveness (VE) estimates from settings with different population characteristics and influenza seasonality remain limited. METHODS:We conducted a test-negative study in Ontario, Canada. All influenza virus tests among infants <6 months from 2010-2019 were identified and linked with health databases to ascertain information on maternal-infant dyads. VE was estimated from the odds ratio for influenza vaccination during pregnancy among cases versus controls, computed using logistic regression with adjustment for potential confounders. RESULTS:Among 23,806 infants tested for influenza, 1,783 (7.5%) were positive and 1,708 (7.2%) were born to mothers vaccinated against influenza during pregnancy. VE against laboratory-confirmed infant influenza infection was 64% (95% confidence interval [CI]: 50%-74%). VE was similar by trimester of vaccination (1st/2nd: 66%, 40%-80%; 3rd: 63%, 46%-74%), infant age at testing (0-<2 months: 63%, 46%-75%; 2-<6 months: 64%, 36%-79%), and gestational age at birth (≥37 weeks: 64%, 50%-75%;  < 37 weeks: 61%, 4%-86%). VE against influenza hospitalization was 67% (95%CI: 50%-78%). CONCLUSIONS:Influenza vaccination during pregnancy offers effective protection to infants <6 months, for whom vaccines are not currently available.

Abstract Background Wastewater (WW)-based surveillance (WBS) of SARS-CoV-2 has been shown to provide a leading indicator to COVID-19 clinical disease including confirmed cases and associated-hospitalizations. To this point, however, longitudinal monitoring of endemic respiratory diseases such as influenza A (IAV) and respiratory syncytial virus (RSV) have minimally been explored. We sought to correlate WW measured endemic virus RNA from municipal WW treatment plants (WWTP) with clinical data to understand WBS performance for endemic respiratory disease in Alberta’s capital city, Edmonton. Methods WW was collected thrice weekly from the two WWTP servicing the Edmonton-area (population ∼1.3 million) between Jan’22 & Feb’23. 24-hour composite samples were processed by Centricon ultracentrifugation, and RNA extracted. IAV, and RSV were quantified in duplicate by established RT-qPCR assays. WW SARS-CoV-2 level values adjusted by population served by each WWTP were compared with clinical cases in sewershed-matched areas in Edmonton Health Zone. Daily IAV and RSV case numbers were generated from IAV and RSV specimen testing data extracted from Alberta Precision Laboratory-Public Health Laboratory and FSA of the specimens was used to create the sewershed-matched case data. Results A total of 361 wastewater samples from the two WWTPs were collected between January 2022 and February 2023: 83 (30%) tested positive for IAV and 185 (51.2%) for RSV. Over two respiratory viral seasons, 2021/2022 and 2022/2023, IAV peaked in May/June 2022 and again in Nov/Dec 2022. IAV and RSV measured in WW positively correlated with daily confirmed clinical cases within the Edmonton Health Zone (Pearson correlation IAV, r2=0.61, p< 0.0001; RSV, r2=0.65, p< 0.0001). Relative to the 2021/2022 season, the WW RSV peak in the 2022/2023 season occurring in November/January was much greater. Figure 1 Population normalized Flu A concentrations in wastewater vs. population normalized case rates in the Edmonton Health Zone. Figure 2 Population normalized RSV concentrations in wastewater vs. population normalized case rates in the Edmonton Health Zone. Conclusion WBS of IAV and RSV demonstrated strong correlations with clinically confirmed diseases in sewershed-matched areas in Edmonton, Alberta. WBS enables objective, inclusive and unbiased monitoring of endemic respiratory viral disease activity. Disclosures All Authors: No reported disclosures

BackgroundA multi-country outbreak of monkeypox virus (MPXV) infections was identified by the World Health Organization in May 2022. The western Canadian province of Alberta identified its first case of MPXV in a returning traveller on June 2, 2022. We undertook a retrospective testing exercise to evaluate whether MPXV may have been circulating in the province earlier.MethodsSkin (genital and non-genital) and mucosal lesion swabs submitted for herpes simplex virus (HSV)/varicella zoster virus (VZV)/syphilis testing from male patients attending sexually-transmitted infection clinics across the province of Alberta from January 28 to May 30, 2022 were retrieved from storage. The population tested was selected based on the epidemiology of the current 2022 multi-country MPXV outbreak. Samples underwent viral nucleic acid extraction and testing for the presence of Orthopoxvirus DNA using a commercial real-time polymerase chain reaction (PCR) kit.ResultsA total of 392 samples (representing 341 unique individuals of median age 31 years) were retrieved. Of them, 349 (89.0%) samples were submitted for HSV/VZV/syphilis testing, 13 (3.3%) for HSV/VZV only, and 30 (7.7%) for syphilis PCR only. None of the 392 samples tested were found to be positive for Orthopoxvirus DNA.ConclusionsThe results of this study indicate that circulation of MPXV in a higher-risk population in Alberta, prior to the first case, was less likely. We recommend that other provinces/territories review their local epidemiology, context and resources prior to conducting similar studies.

Omicron has become the dominant SARS-CoV-2 variant globally since December 2021, with distinct waves being associated with separate Omicron sublineages. Rapid detection of BA.1, BA.2, BA.4, and BA.5 was accomplished in the province of Alberta, Canada, through the design and implementation of real-time reverse transcriptase PCR assays targeting S:N501Y, S:ins214EPE, S:H69/V70, ORF7b:L11F, and M:D3N. Using the combination of results for each of these markers, samples could be designated as belonging to sublineages within BA.1, BA.2, BA.4, or BA.5. The analytical sensitivity of these markers ranged from 132 to 2229 copies/mL and in-laboratory accuracy was 98.9-100%. A 97.3% agreement using 12,592 specimens was demonstrated for the assays compared to genome sequencing. The use of these assays, combined with genome sequencing, facilitated the surveillance of SARS-CoV-2 lineages throughout a BA.5-dominated period.

BACKGROUND:Hyperammonemia syndrome (HS) is a rare post-transplant complication associated with high morbidity and mortality. Its incidence appears to be higher in lung transplant recipients and its pathophysiology is not well understood. In addition to underlying metabolic abnormalities, it is postulated that HS may be associated with Ureaplasma or Mycoplasma spp. lung infections. Management of this condition is not standardized and may include preemptive antimicrobials, renal replacement, nitrogen scavenging, and bowel decontamination therapies, as well as dietary modifications. METHODS:In this case series, we describe seven HS cases, five of whom had metabolic deficiencies ruled out. In addition, a literature review was performed by searching PubMed following PRISMA-P guidelines. Articles containing the terms "hyperammonemia" and "lung" were reviewed from 1 January 1997 to 31 October 2021. RESULTS:All HS cases described in our center had positive airway samples for Mycoplasmataceae, neurologic abnormalities and high ammonia levels post-transplant. Mortality in our group (57%) was similar to that published in previous cases. The literature review supported that HS is an early complication post-transplant, associated with Ureaplasma spp. and Mycoplasma hominis infections and of worse prognosis in patients presenting cerebral edema and seizures. CONCLUSION:This review highlights the need for rapid testing for Ureaplasma spp. and M. hominis after lung transplant, as well as the necessity for future studies to explore potential therapies that may improve outcomes in these patients.

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) causes the global COVID-19 pandemic. Limited studies have been performed on various types of disinfectants utilized to control the spread of this highly contagious virus. This study aimed to investigate the inactivation of SARS-CoV-2 using compressed sodium chloride (CSC) surface. A real-time reverse transcriptase quantitative PCR (RT-qPCR) assay was used to evaluate the effectiveness of CSC on the disintegration of viral RNA in a time dependent manner. The effects of CSC on viral infectivity were determined using a TCID50 assay of a surrogate virus, hCoV-229E, in MRC-5 cell culture. The results demonstrated that CSC achieved a 2 to 3- log10 reduction of viral genomic RNA for a laboratory strain of hCoV-229E, and clinical samples of hCoV-229E and hCoV-OC43. A 3 to 4-log10 reduction was observed for SARS-CoV-2 (RdRp and E gene) suggesting that a CSC surface could effectively disintegrate the SARS-CoV-2 RNA genome. CSC was observed to have a 6 log10 inactivation of infectious hCoV-229E using cell culture after 5 minutes of exposure compared to the control, indicating good disinfection efficacy of a CSC surface against virus.

Wastewater monitoring of SARS-CoV-2 enables early detection and monitoring of the COVID-19 disease burden in communities and can track specific variants of concern. We determined proportions of the Omicron and Delta variants across 30 municipalities covering >75% of the province of Alberta (population 4.5 million), Canada, during November 2021-January 2022. Larger cities Calgary and Edmonton exhibited more rapid emergence of Omicron than did smaller and more remote municipalities. Notable exceptions were Banff, a small international resort town, and Fort McMurray, a medium-sized northern community that has many workers who fly in and out regularly. The integrated wastewater signal revealed that the Omicron variant represented close to 100% of SARS-CoV-2 burden by late December, before the peak in newly diagnosed clinical cases throughout Alberta in mid-January. These findings demonstrate that wastewater monitoring offers early and reliable population-level results for establishing the extent and spread of SARS-CoV-2 variants.

Abstract Background Rapid/point-of-care respiratory virus nucleic acid tests (NAT) may improve oseltamivir, antibiotic, diagnostic test, and hospital bed utilization. Previous randomized controlled trials (RCT) on this topic have not used standard procedures of an accredited healthcare and laboratory system. Methods We conducted a parallel RCT at two hospitals [paediatric = Alberta Children’s Hospital (ACH); primarily adult = Peter Lougheed Centre (PLC)]. Patients with a respiratory viral testing order were randomized to testing at either a central accredited laboratory (standard arm) or with a rapid polymerase chain reaction test at an on-site accredited laboratory followed by standard testing [rapid on-site test (ROST) arm] based on day of specimen receipt at the laboratory. Patients and clinicians were blinded to assignment. The primary outcome for ACH was inpatient length of stay (LOS) and for PLC was the proportion of inpatients prescribed oseltamivir. Results 706 patient encounters were included at ACH; 322 assigned to ROST (181 inpatients) and 384 to the standard arm (194 inpatients). 422 patient encounters were included at PLC; 200 assigned to ROST (157 inpatients) and 222 to the standard arm (175 inpatients). The rate of oseltamivir prescription and number of doses given was reduced in PLC inpatients negative for influenza in the ROST arm compared to standard arm [mean 14.9% (95% CI 9.87–21.9) vs. 27.5% (21.0–35.2), p = 0.0135; mean 2.85 doses (SEM 2.39–3.32) vs. 4.17 doses (3.85–4.49) p = 0.022, respectively]. ROST also significantly reduced oseltamivir use at ACH, reduced chest radiographs (ACH), and laboratory test ordering (PLC), but not antibiotic prescriptions. ROST also reduced the median turnaround time by > 24 h (ACH and PLC). The LOS at ACH was not significantly different between the ROST and standard arms [median 4.05 days (SEM 1.79–18.2) vs 4.89 days (2.07–22.9), p = 0.062, respectively]. No adverse events were reported. Conclusions In a RCT representing implementation of ROST in an accredited laboratory system, we found that a ROST improved oseltamivir utilization and is the first RCT to show reduced ancillary testing in both paediatric and adult populations. A larger study is required to assess reduction in paediatric LOS as ACH was underpowered. These findings help justify the implementation of rapid on-site respiratory virus testing for inpatients. Trial registration ISRCTN, number 10110119, Retrospectively Registered, 01/12/2021.

BACKGROUND:The COVID-19 pandemic has necessitated the need to rapidly make public health decisions. We systematically evaluated SARS-CoV-2 seropositivity to understand local COVID-19 epidemiology and support evidence-based public health decision making. METHODS:Residual blood samples were collected for SARS-CoV-2 receptor binding domain (RBD) IgG testing over a 1-5 day period monthly from 26 February 2021-9 July 2021 from six clinical laboratories across the province of Alberta, Canada. Monthly crude and adjusted (for age and gender) seropositivity were calculated. Results were linked to provincial administrative, laboratory, and vaccine databases. RESULTS:60,632 individual blood samples were tested. Vaccination data were available for 98.8% of samples. Adjusted RBD IgG positivity rose from 11.9% (95% confidence interval [CI] 11.9-12.0%) in March 2021 to 70.2% (95% CI 70.2-70.3%) in July 2021 (p < .0001). Seropositivity rose from 9.4% (95% CI 9.3-9.4%) in March 2021 to 20.2% (95% CI 20.1-20.2%) in July 2021 in unvaccinated Albertans. Unvaccinated seropositive individuals were from geographic areas with significantly (p < .001) lower median household income, lower proportion of married/common-law relationships, larger average household size and higher proportions of visible minorities compared to seronegative unvaccinated individuals. In July 2021, the age groups with the lowest and highest seropositivity in unvaccinated Albertans were those ≥80 years (12.0%, 95% CI 5.3-18.6%) and 20-29 years (24.2%, 95% CI 19.6-28.8%), respectively. Of seropositive unvaccinated individuals, 50.2% (95% CI 45.9-54.5%) had no record of prior SARS-CoV-2 molecular testing. CONCLUSIONS:Longitudinal surveillance of SARS-CoV-2 seropositivity with data linkage is valuable for decision-making during the pandemic.