The Association of Post-COVID-19-Related Symptoms and Preceding Severe Acute Respiratory Syndrome Coronavirus 2 Infection Among Fully Vaccinated Paramedics in Canada.

This study investigated the association between previous severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and risk of symptoms associated with post-COVID conditions among fully vaccinated paramedics in Canada. We included vaccinated paramedics who provided blood sample and questionnaire data on the same date during the study period. We examined the presence of symptoms associated with post-COVID conditions and depression severity against prior SARS-CoV-2 infection categories. Compared to the "no previous SARS-CoV-2 infection" group, there was no detected association between known prior SARS-CoV-2 infection (odds ratio [OR], 1.42 [95% confidence interval {CI}, 0.96-2.09]), nor unknown prior SARS-CoV-2 infection (OR, 0.54 [95% CI, 0.29-1.00]), and the presence of symptoms associated with post-COVID conditions.

Cancer Risks among Emergency Medical Services Workers in Ontario, Canada.

OBJECTIVES: Emergency medical services workers, such as paramedics, provide important emergency care and may be exposed to potential carcinogens while working. Few studies have examined the risk of cancer among paramedics demonstrating an important knowledge gap in existing literature. This study aimed to investigate cancer risks among paramedics in a large cohort of Ontario workers. METHODS: Paramedics were identified in the Occupational Disease Surveillance System (ODSS) from 1996 to 2019. The ODSS was established by linking lost-time worker's compensation claims to administrative health data, including the Ontario Cancer Registry to identify incident cases of cancer. Cox-proportional hazard models were used to calculate age and sex-adjusted hazard ratios and 95% confidence intervals to estimate the risk of cancer among paramedics compared to all other workers in the ODSS. RESULTS: A total of 7240 paramedics were identified, with just over half of the paramedics identifying as male similar to the overall ODSS cohort. Paramedics had a statistically significant elevated risk of any cancer (HR 1.19, 95% CI 1.06-1.34), and elevated risks for melanoma (HR 2.18, 95% CI 1.46-3.26) and prostate cancer (HR 1.73, 95% CI 1.34-2.22). Paramedics had a statistically significant reduced risk for lung cancer (HR 0.48, 95% CI 0.28-0.83). Findings were similar to cancer risks identified in firefighters and police in the same cohort. CONCLUSIONS: This study contributes valuable findings to understanding cancer risks among paramedics and further supports the existing evidence on the increased risk of cancer among emergency medical services workers. We have observed some similar results for firefighters and police, which may be explained by similar exposures, including vehicle exhaust, shiftwork, and intermittent solar radiation. This can lead to a better understanding of carcinogens and other exposures among paramedics and inform cancer prevention strategies.

Effectiveness of dermal cleaning interventions for reducing firefighters' exposures to PAHs and genotoxins.

Firefighters are exposed to carcinogenic and mutagenic combustion emissions, including polycyclic aromatic hydrocarbons (PAHs). Fire service and firefighter cancer advocacy groups recommend skin cleaning using wipes or washing with detergent and water after exposure to smoke, although these strategies have not been proven to reduce exposures to harmful combustion products such as PAHs. This study assessed dermal decontamination methods to reduce PAH exposures by firefighters participating in live fire training scenarios. Study participants (n = 88) were randomly assigned to an intervention group (i.e., two types of commercial skin wipes, detergent and water, or a control group who did not use any skin decontamination). PAHs were measured in personal air (during the fire) and dermal wipe samples (before and after fire suppression and after dermal decontamination). PAH metabolites and mutagenicity were measured in urine samples before and after fire suppression. Airborne PAH concentrations during the fire ranged between 200 and 3,970 µg/m3 (mean = 759 µg/m3, SD = 685 µg/m3). Firefighters had higher total PAHs and high-molecular-weight PAHs on their skin after the fire compared to before (1.3- and 2.2-fold, respectively, p < 0.01). Urinary PAH metabolites increased significantly following exposure to the training fires by 1.7 to 2.2-fold (depending on the metabolite, p < 0.001). Urinary mutagenicity did not differ significantly between pre- and post-fire for any of the decontamination methods. Detergent and water was the only intervention that removed a significant amount of total PAHs from the skin (0.72 ng/cm2 preintervention vs. 0.38 ng/cm2 postintervention, p < 0.01). However, fold changes in urinary PAH metabolites (i.e., pre- vs. post-exposure levels) did not differ among any of the dermal decontamination methods or the control group. These data suggest that despite on-site attempts to remove PAHs from firefighters' skin, the examined interventions did not reduce the internal dose of PAHs. Future work should investigate preventing initial exposure using other interventions, such as improved personal protective equipment.

A Higher Antibody Response Is Generated With a 6- to 7-Week (vs Standard) Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Vaccine Dosing Interval.

The optimal dosing interval for severe acute respiratory syndrome coronavirus 2 vaccines remains controversial. In this prospective study, we compared serology results of paramedics vaccinated with mRNA vaccines at the recommended short (17-28 days) vs long (42-49 days) interval. We found that a long dosing interval resulted in higher spike, receptor binding domain, and spike N terminal domain antibody concentrations.

A Prospective Observational Cohort Comparison of SARS-CoV-2 Seroprevalence Between Paramedics and Matched Blood Donors in Canada During the COVID-19 Pandemic.

STUDY OBJECTIVE: SARS-CoV-2 represents an occupational risk to paramedics, who work in uncontrolled environments. We sought to identify the occupation-specific risk to paramedics by comparing their seroprevalence of SARS-CoV-2 infection-specific antibodies to that of blood donors in Canada. METHODS: In this prospective cohort study, we performed serology testing (Elecsys Anti-SARS-CoV-2 nucleocapsid assay) on samples from paramedics and blood donors (January to July 2021) in Canada. Paramedic samples were compared to blood donor samples through 1:1-matched (based on age, sex, location, date of blood collection, and vaccination status) and raking weighted comparisons. We compared the seroprevalence with a risk difference (and 95% confidence interval [CI]) and performed secondary analyses within subgroups defined by vaccination status. RESULTS: The 1:1 match included 1,627 cases per group; in both groups, 723 (44%) were women, with a median age of 38. The raking weighted comparison included 1,713 paramedic samples and 19,515 blood donor samples, with similar characteristics. In the 1:1 match, the seroprevalence was similar (difference 1.2; 95% CI -0.20 to 2.7) between paramedics (5.2%) and blood donors (3.9%). The raking weighted comparison was consistent (difference 0.97; 95% CI -0.10 to 2.0). The unvaccinated paramedic samples, in comparison to the blood donor samples, demonstrated a higher seroprevalence in the 1:1 (difference 5.9; 95% CI 1.8 to 10) and weighted (difference 6.5; 95% CI 1.8 to 10) comparisons. Among vaccinated cases, the between-group seroprevalence was similar. CONCLUSION: Overall, paramedics demonstrated similar evidence of prior SARS-CoV-2 infection to that of blood donors. However, among unvaccinated individuals, evidence of prior infection was higher among paramedics compared to blood donors.

Occupational Exposure of Canadian Nail Salon Workers to Plasticizers Including Phthalates and Organophosphate Esters.

Personal exposure of nail salon workers to 10 phthalates and 19 organophosphate esters (OPEs) was assessed in 18 nail salons in Toronto, Canada. Active air samplers (n = 60) and silicone passive samplers, including brooches (n = 58) and wristbands (n = 60), were worn by 45 nail salon workers for ∼8 working hours. Diethyl phthalate (median = 471 ng m-3) and diisobutyl phthalate (337 ng m-3) were highest in active air samplers. Most abundant OPEs in active air samplers were tris(2-chloroisopropyl)phosphate or TCIPP (303 ng m-3) and tris(2-chloroethyl)phosphate or TCEP (139 ng m-3), which are used as flame retardants but have not been reported for use in personal care products or nail salon accessories. Air concentrations of phthalates and OPEs were not associated with the number of services performed during each worker's shift. Within a single work shift, a combined total of 16 (55%) phthalates and OPEs were detected on passive silicone brooches; 19 (66%) were detected on wristbands. Levels of tris(2-chloroisopropyl)phosphate, tris(1,3-dichloro-2-propyl)phosphate or TDCIPP, and triphenyl phosphate or TPhP wristbands were significantly higher than those worn by e-waste workers. Significant correlations (p < 0.05) were found between the levels of some phthalates and OPEs in silicone brooches and wristbands versus those in active air samplers. Stronger correlations were observed between active air samplers versus brooches than wristbands. Sampler characteristics, personal characteristics, and chemical emission sources are the three main factors proposed to influence the use of passive samplers for measuring semi-volatile organic compound exposure.

Cancer risk among firefighters and police in the Ontario workforce.

OBJECTIVE: Firefighters and police often work in high-stress, complex environments with known and suspected carcinogenic exposures. We aimed to characterise cancer incidence among firefighters and police. METHODS: The Occupational Disease Surveillance System (ODSS) was used to identify workers employed as firefighters or police in Ontario. A cohort of workers were identified using lost-time workers' compensation claims data and followed for cancer in the Ontario Cancer Registry (1983-2020). Cox proportional hazard models were used to estimate HRs and 95% CIs for primary site-specific cancer diagnoses adjusted for age at start of follow-up, birth year and sex. RESULTS: A total of 13 642 firefighters and 22 595 police were identified in the cohort. Compared with all other workers in the ODSS, firefighters and police had increased risk of prostate cancer (firefighters: HR=1.43, 95% CI 1.31 to 1.57; police: HR=1.47, 95% CI 1.35 to 1.59), colon cancer (firefighters: HR=1.39, 95% CI 1.19 to 1.63; police: HR=1.39, 95% CI 1.21 to 1.60) and skin melanoma (firefighters: HR=2.38, 95% CI 1.99 to 2.84; police: HR=2.27, 95% CI 1.96 to 2.62). Firefighters also had increased risk of cancer of the pancreas, testis and kidney, as well as non-Hodgkin's lymphoma and leukaemia. Police had increased risk of thyroid, bladder and female breast cancer. When compared directly with the police, firefighters had an elevated risk of mesothelioma and testicular cancer. CONCLUSIONS: Firefighters and police demonstrated some similar as well as some unique cancer risks. Findings from this larger worker population may have important implications for workplace and policy-level changes to improve preventative measures and reduce potential exposures to known carcinogenic hazards.

Career fire hall exposures to diesel engine exhaust in Ontario, Canada.

Firefighters are potentially exposed to many carcinogens while at fires. There is also concern that firefighters may be at risk of exposure to carcinogens at other times, such as exposure to diesel engine exhaust (DEE) within fire halls. The study objective was to evaluate DEE levels in career fire halls in Ontario, Canada. Twelve career fire halls from six cities across the province of Ontario, Canada were recruited. In each hall, 24-hr DEE area samples were collected using NIOSH method 5040 (modified) for respirable elemental carbon in three locations (vehicle bay, dormitory, living quarters). Sampling was conducted in both the summer and winter to assess seasonal differences. Factors that may influence DEE exposures were also collected including presence of local exhaust ventilation (LEV), emergency run data, vehicle bay design, and age of fire apparatus. LEV was assessed using a thermo-anemometer during both campaigns. Of the 69 samples collected, 16% had detectable elemental carbon concentrations, where all but one was taken within the vehicle bay (range: <0.5 µg/m3-2.7 µg/m3). The data indicates vehicle bay exposures may be higher in halls with LEV units, those that respond to more emergencies, have a back-in vehicle bay design compared to drive-through design, and during the summer season. Three samples (4.3%) exceeded the 1.03 µg/m3 proposed Dutch occupational exposure limit; however, the estimated exceedance fraction of the underlying vehicle bay exposure distribution was 17%. Eight halls had LEV units, where performance ranged from 3.6% to 85.3% (median = 54%) when compared to manufacturer recommendations. The results show that firefighters may be at an increased risk of exposure to DEE when in fire halls and that LEV units should be assessed regularly for efficiency. Although no occupational exposure limit for DEE is currently available for industrial/non-industrial workplaces in Ontario, fire departments should continue to implement DEE control strategies to reduce exposures to mitigate potential health risks. Additional exposure studies are recommended to better understand DEE exposure in fire halls.

Surveillance of cancer risks for firefighters, police, and armed forces among men in a Canadian census cohort.

BACKGROUND: Firefighters, police, and armed services may be exposed to hazards such as combustion by-products and shift work. METHODS: The CanCHEC cohort linked 1991 census data to the Canadian cancer registry for follow up. Cox proportional hazards modeling was used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) to estimate risks for firefighter, police, or armed forces compared to workers in other occupations. RESULTS: The cohort of 1 108 410 men included 4535 firefighters, 10 055 police, and 9165 armed forces. For firefighters, elevated risks were noted for Hodgkin's lymphoma (HR: 2.89, 95%CI: 1.29-6.46), melanoma (HR: 1.67, 95%CI: 1.17-2.37), and prostate cancer (HR: 1.18, 95%CI: 1.01-1.37). Police had elevated risks for melanoma (HR:1.69, 95%CI: 1.32-2.16) and prostate cancer (HR:1.28, 95%CI: 1.14-1.42). No significant associations were found for armed forces workers. CONCLUSIONS: Canadian firefighters, police, and armed services, may be at an increased risk of developing certain cancers. Results suggested that a healthy worker effect may influence risk estimates.

Elevated Exposures to Polycyclic Aromatic Hydrocarbons and Other Organic Mutagens in Ottawa Firefighters Participating in Emergency, On-Shift Fire Suppression.

Occupational exposures to combustion emissions were examined in Ottawa Fire Service (OFS) firefighters. Paired urine and dermal wipe samples (i.e., pre- and post-event) as well as personal air samples and fire event questionnaires were collected from 27 male OFS firefighters. A total of 18 OFS office workers were used as additional controls. Exposures to polycyclic aromatic hydrocarbons (PAHs) and other organic mutagens were assessed by quantification of urinary PAH metabolite levels, levels of PAHs in dermal wipes and personal air samples, and urinary mutagenicity using the Salmonella mutagenicity assay (Ames test). Urinary Clara Cell 16 (CC16) and 15-isoprostane F2t (8-iso-PGF2α) levels were used to assess lung injury and overall oxidative stress, respectively. The results showed significant 2.9- to 5.3-fold increases in average post-event levels of urinary PAH metabolites, depending on the PAH metabolite (p < 0.0001). Average post-event levels of urinary mutagenicity showed a significant, event-related 4.3-fold increase (p < 0.0001). Urinary CC16 and 8-iso-PGF2α did not increase. PAH concentrations in personal air and on skin accounted for 54% of the variation in fold changes of urinary PAH metabolites (p < 0.002). The results indicate that emergency, on-shift fire suppression is associated with significantly elevated exposures to combustion emissions.

Impact of aggregating exposure information from cases and controls when building a population-based job-exposure matrix from past expert evaluations.

OBJECTIVES: To assess whether the inclusion of data from cases would bias a job-exposure matrix (JEM), we evaluated whether exposures were systematically different between cases and controls from a large historical case-control study. METHODS: Data included 10 381 jobs assessed for occupational exposure to 294 agents within a lung cancer case-control study. For each sex, 1 JEM was developed from case jobs, and 1 from control jobs: with occupation (four-digit occupational codes), time period (1945-1959, 1960-1984, 1985-1995) and agent axes. We estimated concordance in exposure status (defined as probability of exposure threshold ≥5%) and exposure metrics of probability and intensity of exposure, between the 2 JEMs. RESULTS: Of all hypothetical occupation-period-agent combinations, most had no or few observations. Among males there were 8136 common cells (24-occupational codes, 3-periods, 226-agents), containing sufficient observations for comparison with 92% concordance in exposure status; discordance was equally likely to be towards cases or controls. Females had 1710 common cells (9-occupational codes, 3-periods, 114-agents) with 93% concordance in exposure status; discordant cells were more likely to reflect greater exposure among cases. Among concordantly exposed cells, probability and intensity of exposures were highly correlated between the case JEM and control JEM (Kendall τ>0.50), and absolute differences were small (median difference in probability <1.5%, median ratio in intensity=1.00) for both sexes. CONCLUSIONS: Agreement between the case JEM and control JEM was high, suggesting that aggregating the case and control information in our study into a single JEM is justifiable given the benefits of increased sample size.

Risk of chronic obstructive pulmonary disease in a large cohort of Ontario, Canada workers.

Although several occupational exposures have been linked to the risk of COPD; limited data exists on sex-specific differences. This study aimed to identify at-risk occupations and sex differences for COPD risk. Cases were identified in a large surveillance system established through the linkage of former compensation claimants' data (non-COPD claims) to physician visits, ambulatory care data, and hospital inpatient data (1983-2020). Cox proportional hazard models were used to estimate hazard ratios (HRs) and corresponding 95% confidence intervals (CI) for occupation groups (occupation at time of claim), stratified by sex. HRs were indirectly adjusted for cigarette smoking using another population dataset. A total of 29,445 male and 14,693 female incident cases of COPD were identified. Increased risks were observed in both sexes for construction (HRmale 1.15, 95% CI 1.12-1.19; HRfemale 1.54, 95% CI 1.29-1.83) transport/equipment operating (HRmale 1.32, 95% CI 1.28-1.37; HRfemale 1.53, 95% CI 1.40-1.68) farming (HRmale 1.23, 95% CI 1.15-1.32; HRfemale 1.19, 95% CI 1.04-1.37) and janitors/cleaners (HRmale 1.31, 95% CI 1.24-1.37; HRfemale 1.40, 95% CI 1.31-1.49). Increased risks were observed for females employed as chefs and cooks (HR 1.44, 95% CI 1.31-1.58), bartenders (HR 1.38, 95% CI 1.05-1.81), and those working in food/beverage preparation (HR 1.34, 95% CI 1.24-1.45) among other occupations. This study demonstrates elevated risk of COPD among both male and female workers potentially exposed to vapours, gases, dusts, and fumes, highlighting the need for occupational surveillance of COPD.

The relationship between the number of COVID-19 vaccines and infection with Omicron ACE2 inhibition at 18-months post initial vaccination in an adult cohort of Canadian paramedics.

The coronavirus disease 2019 (COVID-19) pandemic, caused by the SARS-CoV-2 virus, has rapidly evolved since late 2019, due to highly transmissible Omicron variants. While most Canadian paramedics have received COVID-19 vaccination, the optimal ongoing vaccination strategy is unclear. We investigated neutralizing antibody (NtAb) response against wild-type (WT) Wuhan Hu-1 and Omicron BA.4/5 lineages based on the number of doses and past SARS-CoV-2 infection, at 18 months post-initial vaccination (with a Wuhan Hu-1 platform mRNA vaccine [BNT162b2 or mRNA-1273]). Demographic information, previous COVID-19 vaccination, infection history, and blood samples were collected from paramedics 18 months post-initial mRNA COVID-19 vaccine dose. Outcome measures were ACE2 percent inhibition against Omicron BA.4/5 and WT antigens. We compared outcomes based on number of vaccine doses (two vs. three) and previous SARS-CoV-2 infection status, using the Mann-Whitney U test. Of 657 participants, the median age was 40 years (IQR 33-50) and 251 (42 %) were females. Overall, median percent inhibition to BA.4/5 and WT was 71.61 % (IQR 39.44-92.82) and 98.60 % (IQR 83.07-99.73), respectively. Those with a past SARS-CoV-2 infection had a higher median percent inhibition to BA.4/5 and WT, when compared to uninfected individuals overall and when stratified by two or three vaccine doses. When comparing two vs. three WT vaccine doses among SARS-CoV-2 negative participants, we did not detect a difference in BA.4/5 percent inhibition, but there was a difference in WT percent inhibition. Among those with previous SARS-CoV-2 infection(s), when comparing two vs. three WT vaccine doses, there was no observed difference between groups. These findings demonstrate that additional Whttps://www.covid19immunitytaskforce.ca/citf-databank/#accessing https://www.covid19immunitytaskforce.ca/citf-databank/#accessinguhan Hu-1 platform mRNA vaccines did not improve NtAb response to BA.4/5, but prior SARS-CoV-2 infection enhances NtAb response.

Eleven-month SARS-CoV-2 binding antibody decay, and associated factors, among mRNA vaccinees: implications for booster vaccination.

Background: We examined the 11 month longitudinal antibody decay among two-dose mRNA vaccinees, and identified factors associated with faster decay. Methods: The study included samples from the COVID-19 Occupational Risk, Seroprevalence and Immunity among Paramedics (CORSIP) longitudinal observational study of paramedics in Canada. Participants were included if they had received two mRNA vaccines without prior SARS-CoV-2 infection and provided two blood samples post-vaccination. The outcomes of interest were quantitative SARS-CoV-2 antibody concentrations. We employed spaghetti and scatter plots (with kernel-weighted local polynomial smoothing curve) to describe the trend of the antibody decay over 11 months post-vaccine and fit a mixed effect exponential decay model to examine the loss of immunogenicity and factors associated with antibody waning over time. Results: This analysis included 652 blood samples from 326 adult paramedics. Total anti-spike antibody levels peaked on the twenty-first day (antibody level 9042 U ml-1) after the second mRNA vaccine dose. Total anti-spike antibody levels declined thereafter, with a half-life of 94 [95 % CI: 70, 143] days, with levels plateauing at 295 days (antibody level 1021 U ml-1). Older age, vaccine dosing interval <35 days, and the BNT162b2 vaccine (compared to mRNA-1273 vaccine) were associated with faster antibody decay. Conclusion: Antibody levels declined after the initial mRNA series with a half-life of 94 days, plateauing at 295 days. These findings may inform the timing of booster vaccine doses and identifying individuals with faster antibody decay.

Firefighting and Cancer: A Meta-analysis of Cohort Studies in the Context of Cancer Hazard Identification.

Objective: We performed a meta-analysis of epidemiological results for the association between occupational exposure as a firefighter and cancer as part of the broader evidence synthesis work of the IARCMonographs program. Methods: A systematic literature search was conducted to identify cohort studies of firefighters followed for cancer incidence and mortality. Studies were evaluated for the influence of key biases on results. Random-effects meta-analysis models were used to estimate the association between ever-employment and duration of employment as a firefighter and risk of 12 selected cancers. The impact of bias was explored in sensitivity analyses. Results: Among the 16 included cancer incidence studies, the estimated meta-rate ratio, 95% confidence interval (CI), and heterogeneity statistic (I2) for ever-employment as a career firefighter compared mostly to general populations were 1.58 (1.14-2.20, 8%) for mesothelioma, 1.16 (1.08-1.26, 0%) for bladder cancer, 1.21 (1.12-1.32, 81%) for prostate cancer, 1.37 (1.03-1.82, 56%) for testicular cancer, 1.19 (1.07-1.32, 37%) for colon cancer, 1.36 (1.15-1.62, 83%) for melanoma, 1.12 (1.01-1.25, 0%) for non-Hodgkin lymphoma, 1.28 (1.02-1.61, 40%) for thyroid cancer, and 1.09 (0.92-1.29, 55%) for kidney cancer. Ever-employment as a firefighter was not positively associated with lung, nervous system, or stomach cancer. Results for mesothelioma and bladder cancer exhibited low heterogeneity and were largely robust across sensitivity analyses. Conclusions: There is epidemiological evidence to support a causal relationship between occupational exposure as a firefighter and certain cancers. Challenges persist in the body of evidence related to the quality of exposure assessment, confounding, and medical surveillance bias.

Evaluation of the Performance of a Multiplexed Serological Assay in the Detection of SARS-CoV-2 Infections in a Predominantly Vaccinated Population.

SARS-CoV-2 seroprevalence studies may be complicated by vaccination efforts. It is important to characterize the ability of serology methods to correctly distinguish prior infection from postvaccination seroreactivity. We report the performance of the Meso Scale Discovery (MSD) V-PLEX COVID-19 Coronavirus Panel 2 IgG assay. Using serum samples from a prospective cohort of paramedics, we calculated the performance of the V-PLEX nucleocapsid ("N") assay to classify prior SARS-CoV-2 infections, defined as a (i) history of a positive SARS-CoV-2 PCR test or (ii) positive serology results using the Roche Elecsys total nucleocapsid anti-SARS-Cov-2 assay. We calculated sensitivity and specificity at the optimal threshold (defined by the highest Youden index). We compared subgroups based on vaccination status, and between models that excluded prior infections 3 to 12 months before sample collection. Of 1119 participants, 914 (81.7%) were vaccinated and 60 (5.4%) had evidence of a preceding SARS-CoV-2 infection. Overall and within vaccinated and unvaccinated subgroups, the optimal thresholds were 828 AU/mL, 827 AU/mL, and 1324 AU/mL; with sensitivities of 0.95 (95% CI: 0.94 to 0.96), 0.95 (0.94 to 0.96), 0.94 (0.92 to 0.96) and specificities of 0.88 (0.86 to 0.90), 0.87 (0.85 to 0.89), and 0.94 (0.89 to 0.98), respectively. N-assay specificity was significantly better in unvaccinated (versus vaccinated) individuals (P = 0.005). Overall optimal thresholds based on the AUC values were higher for samples from unvaccinated participants, especially when examining infections within the preceding 9 months (5855 versus 1704 AU/mL). Overall, V-PLEX nucleocapsid assay cutoff values were higher among unvaccinated individuals. Specificity was also significantly higher among unvaccinated individuals. Different thresholds were required to achieve optimal test performance, especially for detecting SARS-CoV-2 infections within the preceding 9 months. IMPORTANCE Among a cohort of adult paramedics in Canada, we investigated the performance of nucleocapsid (N) antibody detection (measured with a V-PLEX assay) to identify previous COVID-19 infections and compared differences among vaccinated and unvaccinated. Our data indicate that vaccinated and unvaccinated groups require different thresholds to achieve optimal test performance, especially for detecting COVID-19 within the preceding 9 months. Overall, specificity was significantly higher among unvaccinated, compared to vaccinated individuals.