Hybrid immunity from SARS-CoV-2 infection and vaccination in Canadian adults: cohort study.

Background: Few national-level studies have evaluated the impact of 'hybrid' immunity (vaccination coupled with recovery from infection) from the Omicron variants of SARS-CoV-2.Methods: From May 2020 to December 2022, we conducted serial assessments (each of ~4000-9000 adults) examining SARS-CoV-2 antibodies within a mostly representative Canadian cohort drawn from a national online polling platform. Adults, most of whom were vaccinated, reported viral test-confirmed infections and mailed self-collected dried blood spots to a central lab. Samples underwent highly sensitive and specific antibody assays to spike and nucleocapsid protein antigens, the latter triggered only by infection. We estimated cumulative SARS-CoV-2 incidence prior to the Omicron period and during the BA.1/1.1 and BA.2/5 waves. We assessed changes in antibody levels and in age-specific active immunity levels.Results: Spike levels were higher in infected than in uninfected adults, regardless of vaccination doses. Among adults vaccinated at least thrice and infected more than six months earlier, spike levels fell notably and continuously for the nine months post-vaccination. By contrast, among adults infected within six months, spike levels declined gradually. Declines were similar by sex, age group, and ethnicity. Recent vaccination attenuated declines in spike levels from older infections. In a convenience sample, spike antibody and cellular responses were correlated. Near the end of 2022, about 35% of adults above age 60 had their last vaccine dose more than six months ago, and about 25% remained uninfected. The cumulative incidence of SARS-CoV-2 infection rose from 13% (95% CI 11-14%) before omicron to 78% (76-80%) by December 2022, equating to 25 million infected adults cumulatively. However, the COVID-19 weekly death rate during the BA.2/5 waves was less than half of that during the BA.1/1.1 wave, implying a protective role for hybrid immunity.Conclusions: Strategies to maintain population-level hybrid immunity require up-to-date vaccination coverage, including among those recovering from infection. Population-based, self-collected dried blood spots are a practicable biological surveillance platform.Funding: Funding was provided by the COVID-19 Immunity Task Force, Canadian Institutes of Health Research, Pfizer Global Medical Grants, and St. Michael's Hospital Foundation. PJ and ACG are funded by the Canada Research Chairs Program.

Deep Brain Stimulation for Primary Refractory Tinnitus: A Systematic Review.

BACKGROUND: tinnitus is a common and often debilitating condition with limited evidence-based treatment options. Deep brain stimulation (DBS) is an approved treatment modality for certain neurological conditions; its experimental use as a treatment modality for severe tinnitus is novel and beginning to show promise. This systematic review focuses on the current evidence for the safety and efficacy of DBS for treatment of refractory tinnitus. METHODS: a systematic search in PubMed and EMBASE was performed to identify peer-reviewed studies on DBS of non-cortical structures for the primary indication of tinnitus treatment. Three studies were identified as meeting these criteria, one of which had two related sub-studies. RESULTS: seven patients with available data who underwent DBS for tinnitus were identified. DBS targets included nucleus accumbens (NAc), ventral anterior limb of the internal capsule (vALIC), caudate nucleus, and the medial geniculate body (MGB) of the thalamus. All studies used the Tinnitus Functional Index (TFI) as a primary outcome measure. DBS of the caudate was most commonly reported (n = 5), with a mean TFI improvement of 23.3 points. Only one subject underwent DBS targeting the NAc/vALIC (extrapolated TFI improvement 46.8) and one subject underwent DBS targeting the MGB (TFI improvement 59 points). CONCLUSIONS: DBS is a promising treatment option for refractory subjective tinnitus, with early data, from small patient cohorts in multiple studies, suggesting its safety and efficacy. Further studies with a larger patient population are needed to support this safety and efficacy before implementing this treatment to daily practice.

Ergonomics in Spine Surgery: A Systematic Review.

STUDY DESIGN: Systematic Review. OBJECTIVE: This systematic review aims to synthesize existing studies and highlight the significance of ergonomic considerations for spine surgeons' well-being and the impact on patient outcomes. SUMMARY OF BACKGROUND DATA: Spine surgery is a physically demanding field that poses several risks to surgeons, particularly with musculoskeletal disorders. Despite the well-documented consequences of musculoskeletal injuries endured by surgeons, surgical ergonomics in spine surgery has received limited attention. METHODS: Following PRISMA guidelines, a comprehensive literature search was conducted in PubMed and Embase. Studies focusing on surgeon ergonomics in spine surgery were selected. Data extracted included study details, surgeon demographics, ergonomic factors, and outcomes. Qualitative analysis was performed due to the heterogeneous nature of study designs and criteria. RESULTS: Eleven studies met inclusion criteria. Six studies utilized surveys to explore physical challenges, prevalence rates of pain, work practices, and ergonomic tools. Two studies employed optoelectronic motion analysis to assess spinal angles of the surgeon during surgery. Two studies assesed ergonomics in different visualization methods using rapid entire body assessment (REBA). One study applied video analysis to scrutinize surgeons' neck postures during the case. The results demonstrated a varying prevalence and diverse presentations of musculoskeletal disorders, varying impact on surgical performance, and nuanced relationships between experience, workload, and ergonomic concerns. CONCLUSION: This systematic review summarizes the heterogenous evaluations of ergonomics in spine surgery. Overall, upwards of three-quarters of spine surgeons have reported musculoskeletal discomfort, most commonly presented as back pain, neck pain, and hand/wrist discomfort. These symptoms are often exacerbated by the use of loupes, operating bed height, and extended period of times in various positions. Studies demonstrate that the physical discomfort is associated with the surgeons' mental and emotional well-being, leading to stress, burnout, and reduced job satisfaction; all of which impact patient care.

Are Variable Screw Angle Change and Screw-to-Vertebral Body Ratio Associated With Radiographic Subsidence Following Anterior Cervical Discectomy and Fusion?

STUDY DESIGN: Retrospective Cohort. OBJECTIVE: This study aims to assess the easily measurable radiographic landmarks of screw-to-vertebral body ratio and changes in screw angle to identify if they are associated with early subsidence following an Anterior cervical discectomy and fusion (ACDF). METHODS: A retrospective cohort study was conducted on patients undergoing 1-3 level ACDF with allograft or PEEK cages. Preoperative, immediate postoperative, and 6-month postoperative radiographs were analyzed to measure intradiscal height (or distance between 2 vertebral bodies) as an anterior vertebral distance (AVD), middle (MVD), and posterior (PVD), screw angle, screw-to-vertebral body length ratio, and interscrew distance. Multivariate stepwise regression analyses were performed. RESULTS: 92 patients were included (42 single-level, 32 two-level, and 18 3-level ACDFs). In single-level ACDFs, a decrease in the caudal screw angle was associated with a decrease in AVD (=.001) and MVD (P = .03). A decrease in the PVD was associated with a decrease in segmental lordosis (P < .001). For two-level ACDFs, a higher caudal screw-to-body ratio was associated with a lower MVD (P = .01). CONCLUSION: Six months following an ACDF for degenerative pathology, a decrease in the caudal screw angle was associated with an increase in radiographic subsidence at the antero-medial aspect of the disc space albeit largely subclinical. This suggests that the caudal screw angle change may serve as a reliable radiographic marker for early radiographic subsidence. Furthermore, a greater screw-to-vertebral body ratio may be protective against radiographic subsidence in two-level ACDF procedures.

Implementation of the Modified Brain Injury Guidelines Might Be Feasible and Cost-Effective Even in a Nontrauma Hospital.

INTRODUCTION: The modified Brain Injury Guidelines (mBIG) provide a framework to stratify traumatic brain injury (TBI) patients based on clinical and radiographic factors in level 1 and 2 trauma centers. Approximately 75% of all U.S. hospitals do not carry any trauma designation yet could also benefit from these guidelines. To the best of our knowledge, this is the first report of applying the mBIG protocol in a community hospital without any trauma designation. METHODS: All adult patients with a TBI in a single center from 2020 to 2022 were retrospectively classified into mBIG categories. The primary outcomes included neurological deterioration, progression on computed tomography of the head, and surgical intervention. Additional outcomes included the hospital costs incurred by the mBIG 1 and mBIG 2 groups. RESULTS: Of the 116 included patients, 35 (30%) would have stratified into mBIG 1, 23 (20%) into mBIG 2, and 58 (50%) into mBIG 3. No patient in mBIG 1 had a decline in neurological examination findings or progression on computed tomography of the head or required neurosurgical intervention. Three patients in mBIG 2 had radiographic progression and one required surgical decompression. Two patients in mBIG 3 demonstrated a neurological decline and six had radiographic progression. Of the 21 patients who received surgical intervention, 20 were stratified into mBIG 3. Implementation of the mBIG protocol could have reduced costs by >$250,000 during the 2-year period. CONCLUSIONS: The mBIG protocol can safely stratify patients in a nontrauma hospital. Because nontrauma centers tend to see more patients with minor TBIs, implementation could result in significant cost savings, reduce unnecessary hospital and intensive care unit resources, and reduce transfers to a tertiary institution.

Opiate-reduction protocol for common outpatient spinal procedures: a long-term feasibility study and single-center experience.

OBJECTIVE: The opioid epidemic continues to be at the forefront of public health. As a response to this crisis, many statewide and national medical groups have sought to develop opioid-prescribing guidelines for both acute and chronic pain states. Given the lack of evidence in the neurosurgical landscape, the authors' institution implemented opioid-prescribing guidelines for common outpatient spinal procedures in 2017, subsequently demonstrating a significant reduction in the narcotics prescribed. However, the ability to maintain the results garnered from such guidelines long term has not been described. The objective of this study was to evaluate postoperative opioid utilization at a high-volume quaternary referral center 5 years after the initial implementation of an opioid-reduction protocol for common outpatient spinal procedures. METHODS: From the electronic medical records, authors collected data on the number of tablets and total morphine equivalent dose (MED) prescribed, acute postoperative readmissions for pain concerns, refill requests, and conversion to long-term opiate use in the 5 years following implementation of an opioid-reduction protocol for common outpatient spinal procedures. These procedures, undertaken in opiate-naive patients, included 1- or 2-level anterior cervical discectomy and fusion, 1- or 2-level cervical disc replacement, and 1- or 2-level laminectomy, laminotomy, or foraminotomy (cervical or lumbar). RESULTS: The total quantity of narcotics was reduced by 37.0 tablets per patient after protocol implementation and over the 5-year period thereafter. Generally, patients were discharged with an average of 23.3 tablets, concurrent with the initial goal of 24 tablets, set forth in 2017. These results confirm an ongoing reduction in opiate quantities prescribed and overall morphine equivalent totals at the time of discharge over the course of 5 years after initial protocol implementation. CONCLUSIONS: A standardized discharge protocol for postoperative outpatient spinal procedures can lead to long-term reductions in opioid discharge quantity, without compromising patient safety or increasing the utilization of hospital resources through readmissions, refill requests, or clinic phone calls. This study provides an example of a feasible and effective discharge prescription regimen that may be generalizable to common outpatient neurosurgical procedures with long-term evidence that a small intervention can lead to ongoing reduced quantities of postoperative opioids at the time of discharge.

A Tubular-Mounted Digital Camera Versus Optical Surgical Microscope for Minimally Invasive Lumbar Decompression Surgery: The Impact on Operative Times, Ergonomics, and Workflow.

OBJECTIVE: Understanding ergonomic impact is foundational to critically evaluating value and safety of enabling technologies in minimally invasive spine surgeries. This study assessed the impact of a tubular-mounted digital camera (TMDC) versus an optical surgical microscope (OSM) in single-level minimally invasive spine surgeries on operative times, durotomy rate, surgeon ergonomics, safety, and operating room workflow. METHODS: This retrospective study compared consecutive single-level minimally invasive lumbar decompression surgeries in a TMDC cohort (September 2021-June 2022) with an historical OSM cohort (January 2020-July 2021). Data included patient demographics, operative times, durotomy incidence, surgeon ergonomics (Rapid Entire Body Assessment scores), and equipment impact via staff surveys. Operative times were assessed by t test, while Pearson χ2 test compared sex. Age, body mass index, and Charlson Comorbidity Index comparisons were made by Wilcoxon rank sum tests, and survey results were analyzed with Wilcoxon signed rank tests. RESULTS: TMDC and OSM groups included 74 and 82 patients, respectively. Age, sex, and Charlson Comorbidity Index did not significantly differ between groups. The TMDC group had a higher body mass index (29.6 ± 5.1) than the OSM group (29.0 ± 7.5) (P = 0.04). The TMDC group had significantly shorter operative times (57.3 ± 16.6 minutes) than the OSM group) (66.7 ± 22.5 minutes) (P = 0.004), with no difference in durotomy rates (P = 0.42). TMDC use yielded lower Rapid Entire Body Assessment scores compared with OSM (4.1 ± 0.77) (P < 0.001). Surveys indicated improved safety, setup time, and workflow with TMDC (P < 0.001). CONCLUSIONS: TMDC in single-level minimally invasive lumbar decompression surgery improved surgeon ergonomics, reduced operative times, and maintained durotomy rates, enhancing operating room efficiency. Evaluating ergonomic impact of technology is vital for safety and value assessment.

Is spinopelvic mismatch associated with increased disability at 2 years following short-segment lumbar fusions?

OBJECTIVE: This study aimed to investigate the impact of pelvic incidence (PI) and lumbar lordosis (LL) matching on health-related quality of life (HRQOL) outcomes in patients undergoing one- or two-level lumbar fusions for degenerative pathology. The study also examined changes in alignment and HRQOL over a 24-month follow-up period. METHODS: A retrospective cohort study used data from a multicenter, prospectively collected database. Radiographic parameters were measured preoperatively and at 3-month and 24-month postoperative time points. Patients were categorized as having alignment (PI-LL ≤ 10°) or malalignment (PI-LL > 10°) at all time points. The Oswestry Disability Index scores were collected at the same time points. Statistical analyses assessed differences in HRQOL scores and radiographic parameters between the aligned and malaligned groups. RESULTS: Seventy-six patients were included. Both the aligned and malaligned groups showed improved HRQOL scores after surgery, but patients with proper alignment (PI-LL ≤ 10°) had significantly better HRQOL scores at the 24-month follow-up. Alignment remained stable from 3 months to 24 months postoperatively, with minimal movement between the aligned and malaligned groups. CONCLUSIONS: Proper PI-LL matching in one- and two-level lumbar fusions for degenerative pathology leads to improved HRQOL outcomes at the 24-month follow-up. Patients with maintained proper alignment after surgery experience continued improvement in disability levels. Surgeons should consider longer follow-up for patients who do not achieve proper alignment initially, as 24 months is crucial for assessing the consequences of malalignment in short-segment lumbar fusions.

A Bayesian approach to estimating COVID-19 incidence and infection fatality rates.

Naive estimates of incidence and infection fatality rates (IFR) of coronavirus disease 2019 suffer from a variety of biases, many of which relate to preferential testing. This has motivated epidemiologists from around the globe to conduct serosurveys that measure the immunity of individuals by testing for the presence of SARS-CoV-2 antibodies in the blood. These quantitative measures (titer values) are then used as a proxy for previous or current infection. However, statistical methods that use this data to its full potential have yet to be developed. Previous researchers have discretized these continuous values, discarding potentially useful information. In this article, we demonstrate how multivariate mixture models can be used in combination with post-stratification to estimate cumulative incidence and IFR in an approximate Bayesian framework without discretization. In doing so, we account for uncertainty from both the estimated number of infections and incomplete deaths data to provide estimates of IFR. This method is demonstrated using data from the Action to Beat Coronavirus erosurvey in Canada.

Monthly multidisciplinary complex spine conference: a cost-analysis utilizing time-driven activity-based costing.

PURPOSE: To understand costs and provide an initial framework associated with conference implementation as it pertains to complication prevention. METHODS: Team members' time spent on conference preparation, presentation, and follow-up tasks was recorded and averaged to determine the time required to prepare and present one patient. Using 2022 hourly wage rates based on our urban hospital setting, wage values were calculated for each personnel type and applied to their time spent. The total cost of the conference was annualized and calculated from the time spent in the three phases of the conference multiplied by the wage rate. Published data on complication rates and associated costs before and after conference implementation were used to calculate total cost reduction. RESULTS: With 3 active spine surgeons and 108 patients per year, the total time investment was 104.04 min per patient, costing $21,791 annually. Total RN equivalent value per patient was 5.25 for all three phases. Using a historical model, this multidisciplinary approach for adult spinal deformity reduced complications by 51% at 30 days, resulting in cost savings of $418,518 per year. Thus, the model demonstrates that implementation of this approach resulted in a potential total savings of $396,726/year. CONCLUSION: Implementing a cost-saving tool for managing complex spinal disorders is a responsibility of the spine team, who should lead a multidisciplinary conference. The combination of TDABC and lean methodology can effectively demonstrate the variable costs associated with this multidisciplinary effort and models provide evidence of potential cost-savings when applied to a multidisciplinary adult spinal deformity conference. These findings should encourage clinicians and administrators to allocate resources to improve patient care by reducing complications and costs.

Early Compensatory Segmental Angle Changes at L3-4 and L4-5 Following a L5-S1 Interbody Fusion for a Grade 1 Spondylolisthesis.

STUDY DESIGN: Retrospective study included patients who underwent a L5-S1 ALIF or TLIF with posterior pedicle screw instrumentation for grade 1 spondylolisthesis 2018-2022. OBJECTIVE: To compare early reciprocal changes at the L3-4 and L4-5 adjacent levels six months after anterior (ALIF) or transforaminal (TLIF) lumbar interbody fusion at L5-S1. BACKGROUND: Degenerative and chronic isthmic spondylolistheses often result in decreased segmental lordosis at L5-S1. This can lead to lordotic overcompensation at adjacent levels to maintain spinopelvic balance. However, the fate of adjacent angles following interbody fusion is not well understood. METHODS: Preoperative and 6-month postoperative measurements of segmental lordosis (L3-4, L4-5, and L5-S1), lumbar lordosis, and pelvic incidence were obtained from sagittal standing radiographs. Preliminary t-tests were performed for descriptive purposes, and multiple regression was used for hypothesis testing. RESULTS: Ninety-eight patients met the inclusion criteria (50 ALIF and 48 TLIF). A greater amount of lordosis achieved at L5-S1 was significantly associated with a greater reduction of segmental lordosis at L4-5 (r=-0.65, P<.001) or L3-4 (r=-0.46, P<.001) (Fig. 3A). A greater preoperative PI was associated with a greater reduction of segmental lordosis at L4-L5 (r=-0.42, P<.001) and at L3-L4 (r=-0.44, P<.001). CONCLUSION: At six months following a lumbar interbody fusion at L5-S1, greater compensatory changes with lordosis reduction are observed at the supra-adjacent L4-5 and L3-4 levels in patients achieving greater L5-S1 segmental lordosis. Additionally, preoperative pelvic incidence (PI) played a role in influencing lordotic correction.

Clinical Guidelines for the Evaluation and Treatment of Lumbar Disc Herniations: How Accurate is the Internet?

OBJECTIVE: To compare information online regarding lumbar disc herniation (LDH) on commonly searched websites and compare those findings with the evidence-based recommendations listed in the North American Spine Society (NASS) clinical practice guidelines. METHODS: NASS Clinical Practice Guidelines, Internet searches were performed utilizing three common search engines (Google, Bing, Yahoo) and keywords associated with LDH. The top 20 websites from each search were selected. The content regarding diagnosis and treatment of LDH was compared to the NASS clinical practice guidelines. RESULTS: On average, websites mentioned only 59% of recommendations supported by Level I evidence. Websites included an average of 3 recommendations not discussed in the NASS guidelines out of an average of 12 total recommendations. Muscle and sensory testing and physical therapy were the most frequent recommendations, appearing on over 80% of websites. Websites were equally likely to contain recommendations backed by high-quality evidence as recommendations not included in NASS guidelines. CONCLUSIONS: This study demonstrates that websites regarding LDH contain a mix of information, with only a fraction of recommendations aligning with NASS clinical guidelines. Patients who use these websites are presented with unsubstantiated information, conceivably impacting their understanding, expectations and decision-making in physician offices.

Pre-Stimulus Power but Not Phase Predicts Prefrontal Cortical Excitability in TMS-EEG.

The cortical response to transcranial magnetic stimulation (TMS) has notable inter-trial variability. One source of this variability can be the influence of the phase and power of pre-stimulus neuronal oscillations on single-trial TMS responses. Here, we investigate the effect of brain oscillatory activity on TMS response in 49 distinct healthy participants (64 datasets) who had received single-pulse TMS over the left dorsolateral prefrontal cortex. Across all frequency bands of theta (4-7 Hz), alpha (8-13 Hz), and beta (14-30 Hz), there was no significant effect of pre-TMS phase on single-trial cortical evoked activity. After high-powered oscillations, whether followed by a TMS pulse or not, the subsequent activity was larger than after low-powered oscillations. We further defined a measure, corrected_effect, to enable us to investigate brain responses to the TMS pulse disentangled from the power of ongoing (spontaneous) oscillations. The corrected_effect was significantly different from zero (meaningful added effect of TMS) only in theta and beta bands. Our results suggest that brain state prior to stimulation might play some role in shaping the subsequent TMS-EEG response. Specifically, our findings indicate that the power of ongoing oscillatory activity, but not phase, can influence brain responses to TMS. Aligning the TMS pulse with specific power thresholds of an EEG signal might therefore reduce variability in neurophysiological measurements and also has the potential to facilitate more robust therapeutic effects of stimulation.

Homogeneous surrogate virus neutralization assay to rapidly assess neutralization activity of anti-SARS-CoV-2 antibodies.

The COVID-19 pandemic triggered the development of numerous diagnostic tools to monitor infection and to determine immune response. Although assays to measure binding antibodies against SARS-CoV-2 are widely available, more specific tests measuring neutralization activities of antibodies are immediately needed to quantify the extent and duration of protection that results from infection or vaccination. We previously developed a 'Serological Assay based on a Tri-part split-NanoLuc® (SATiN)' to detect antibodies that bind to the spike (S) protein of SARS-CoV-2. Here, we expand on our previous work and describe a reconfigured version of the SATiN assay, called Neutralization SATiN (Neu-SATiN), which measures neutralization activity of antibodies directly from convalescent or vaccinated sera. The results obtained with our assay and other neutralization assays are comparable but with significantly shorter preparation and run time for Neu-SATiN. As the assay is modular, we further demonstrate that Neu-SATiN enables rapid assessment of the effectiveness of vaccines and level of protection against existing SARS-CoV-2 variants of concern and can therefore be readily adapted for emerging variants.

Assessment of SARS-CoV-2 Seropositivity During the First and Second Viral Waves in 2020 and 2021 Among Canadian Adults.

Importance: The incidence of infection during SARS-CoV-2 viral waves, the factors associated with infection, and the durability of antibody responses to infection among Canadian adults remain undocumented. Objective: To assess the cumulative incidence of SARS-CoV-2 infection during the first 2 viral waves in Canada by measuring seropositivity among adults. Design, Setting, and Participants: The Action to Beat Coronavirus study conducted 2 rounds of an online survey about COVID-19 experience and analyzed immunoglobulin G levels based on participant-collected dried blood spots (DBS) to assess the cumulative incidence of SARS-CoV-2 infection during the first and second viral waves in Canada. A sample of 19 994 Canadian adults (aged ≥18 years) was recruited from established members of the Angus Reid Forum, a public polling organization. The study comprised 2 phases (phase 1 from May 1 to September 30, 2020, and phase 2 from December 1, 2020, to March 31, 2021) that generally corresponded to the first (April 1 to July 31, 2020) and second (October 1, 2020, to March 1, 2021) viral waves. Main Outcomes and Measures: SARS-CoV-2 immunoglobulin G seropositivity (using a chemiluminescence assay) by major geographic and demographic variables and correlation with COVID-19 symptom reporting. Results: Among 19 994 adults who completed the online questionnaire in phase 1, the mean (SD) age was 50.9 (15.4) years, and 10 522 participants (51.9%) were female; 2948 participants (14.5%) had self-identified racial and ethnic minority group status, and 1578 participants (8.2%) were self-identified Indigenous Canadians. Among participants in phase 1, 8967 had DBS testing. In phase 2, 14 621 adults completed online questionnaires, and 7102 of those had DBS testing. Of 19 994 adults who completed the online survey in phase 1, fewer had an educational level of some college or less (4747 individuals [33.1%]) compared with the general population in Canada (45.0%). Survey respondents were otherwise representative of the general population, including in prevalence of known risk factors associated with SARS-CoV-2 infection. The cumulative incidence of SARS-CoV-2 infection among unvaccinated adults increased from 1.9% in phase 1 to 6.5% in phase 2. The seropositivity pattern was demographically and geographically heterogeneous during phase 1 but more homogeneous by phase 2 (with a cumulative incidence ranging from 6.4% to 7.0% in most regions). The exception was the Atlantic region, in which cumulative incidence reached only 3.3% (odds ratio [OR] vs Ontario, 0.46; 95% CI, 0.21-1.02). A total of 47 of 188 adults (25.3%) reporting COVID-19 symptoms during phase 2 were seropositive, and the OR of seropositivity for COVID-19 symptoms was 6.15 (95% CI, 2.02-18.69). In phase 2, 94 of 444 seropositive adults (22.2%) reported having no symptoms. Of 134 seropositive adults in phase 1 who were retested in phase 2, 111 individuals (81.8%) remained seropositive. Participants who had a history of diabetes (OR, 0.58; 95% CI, 0.38-0.90) had lower odds of having detectable antibodies in phase 2. Conclusions and Relevance: The Action to Beat Coronavirus study found that the incidence of SARS-CoV-2 infection in Canada was modest until March 2021, and this incidence was lower than the levels of population immunity required to substantially reduce transmission of the virus. Ongoing vaccination efforts remain central to reducing viral transmission and mortality. Assessment of future infection-induced and vaccine-induced immunity is practicable through the use of serial online surveys and participant-collected DBS.