Comparative analysis of pediatric Respiratory Syncytial Virus epidemiology and clinical severity before and during the COVID-19 pandemic in British Columbia, Canada (preprint)

BackgroundThe COVID-19 pandemic affected Respiratory Syncytial Virus (RSV) circulation and surveillance, causing logistical complexity for health systems. Our objective was to describe changes in epidemiology and clinical severity of RSV cases in British Columbia, Canada. MethodsComparative analysis of RSV detections in children <36 months at BC Childrens Hospital (BCCH) between September 1 and August 31 of 2017-18, 2018-19, 2019-20, 2020-21 and 2021-22. ResultsAbout one-fifth of children tested RSV positive on average across all periods. The median age of RSV cases was 11.8 [IQR: 3.8-22.3] months in 2021-22 versus 6.3 [IQR: 1.9-16.7] months in 2017-20 (p<0.001). Increased testing in 2021-22 (n=3,120) compared to 2017-20 (average n=1,222/period) detected milder infections with lower proportion hospitalized in all age subgroups <6 (26.0%), 6-11 (12.3%), 12-23 (12.2%) and 24-35 (16.0%) months versus 2017-20 (49.3%, 53.5%, 62.6%, 57.5%, respectively) (all p<0.001). Children <6 months consistently comprised most hospitalizations and those born prematurely <29 weeks or with chronic respiratory co-morbidities remained at highest hospitalization risk in 2021-22. Among hospitalized cases, intensive care, respiratory support or supplemental oxygen use did not differ between the 2017-20 and 2021-22 periods. ConclusionsRSV circulation halted during the pandemic, but with the lifting of mitigation measures a subsequent resurgence in children <36 months of age was accompanied by shift toward older (24-35 month) cases in 2021-22, without increased severity. For the 2022-23 period, increased circulation and residual vulnerability in additional birth cohorts spared from RSV infection during the pandemic could have marked cumulative healthcare impact, even without increase in proportion hospitalized.

Characterizing Longitudinal Antibody Responses in Recovered Individuals Following COVID-19 Infection and Single-Dose Vaccination in British Columbia, Canada: a Prospective Cohort Study (preprint)

Background: Investigating antibody titres in individuals who have been both naturally infected with SARS-CoV-2 and vaccinated can provide insight into antibody dynamics and correlates of protection over time. Methods: Human coronavirus (HCoV) IgG antibodies were measured longitudinally in a prospective cohort of PCR-confirmed, COVID-19 recovered individuals (k=57) in British Columbia pre- and post-vaccination. SARS-CoV-2 and endemic HCoV antibodies were measured in serum collected between Nov. 2020 and Sept. 2021 (n=341). Primary analysis used a linear mixed-effects model to understand the effect of single dose vaccination on antibody concentrations adjusting for biological sex, age, time from infection and vaccination. Secondary analysis investigated the cumulative incidence of high SARS-CoV-2 anti-spike IgG seroreactivity equal to or greater than 5.5 log10 AU/mL up to 105 days post-vaccination. No re-infections were detected in vaccinated participants, post-vaccination by qRT-PCR performed on self-collected nasopharyngeal specimens. Results: Bivariate analysis (complete data for 42 participants, 270 samples over 472 days) found SARS-CoV-2 spike and RBD antibodies increased 14-56 days post-vaccination (p<0.001) and vaccination prevented waning (B=1.66 [95%CI: 1.45-3.46]); while decline of nucleocapsid antibodies over time was observed (B=-0.24 [95%CI: -1.2-(-0.12)]). A non-significant trend towards higher spike antibodies against endemic beta-HCoVs was also noted. On average, SARS-CoV-2 anti-spike IgG concentration increased in participants who received one vaccine dose by 2.06 log10 AU/mL (95%CI: 1.45-3.46) adjusting for age, biological sex, and time. Cumulative incidence of high SARS-CoV-2 spike antibodies (>5.5 log10 AU/mL) was 83% greater in vaccinated compared to unvaccinated individuals. Conclusions: Our study confirms that vaccination post-SARS-CoV-2 infection provides multiple benefits, such as increasing anti-spike IgG titers and preventing decay up to 85 days post-vaccination.

SARS-CoV-2 seroprevalence among public school staff in Metro Vancouver after the first Omicron wave in British Columbia, Canada (preprint)

ObjectiveTo determine the SARS-CoV-2 seroprevalence among school workers in the setting of full in-person schooling and the highly transmissible Omicron variants of concern. DesignCross-sectional study among school staff, comparing to period-, age-, sex- and postal code-weighted data from Canadian blood donors from the same community. SettingThree large school districts in the greater Vancouver metropolitan area, British Columbia, Canada, with serology sampling done between January 26, 2022 and April 8, 2022. ParticipantsSchool staff actively working in the Vancouver, Richmond and Delta School Districts. Main outcome measureSARS-CoV-2 seroprevalence based on nucleocapsid (N)-protein testing, adjusted for the sensitivity and specificity of the assay. ResultsA majority (65.8%) of the 1845 school staff enrolled reported close contact with a COVID-19 case outside the household. Of those, about half reported close contact with a COVID-19 case at school either in a student (51.5%) or co-worker (54.9%). In a representative sample of 1620 (87.8%) school staff, the adjusted seroprevalence was 26.5% [95%CrI: 23.9 - 29.3%]. This compared to an age, sex and residency area-weighted seroprevalence of 32.4% [95%CrI: 30.6 - 34.5%] among 7164 blood donors. ConclusionDespite frequent COVID-19 exposures, the prevalence of SARS-CoV-2 infections among the staff of three main school districts in the Vancouver metropolitan area was no greater than a reference group of blood donors, even after the emergence of the more transmissible Omicron variant. What is already known on this subject?O_LIEarlier studies indicate that COVID-19 infection rates are not increased among school staff at previous stages of the pandemic compared to the community, yet controversy remains whether this will remain true after the emergence of the highly transmissible Omicron variant. C_LI What this study adds?O_LIDespite frequent COVID-19 exposures, this study identified no detectable increase in SARS-CoV-2 seroprevalence among school staff working in three metro Vancouver public school districts after the first Omicron wave in British Columbia, compared to a reference group of blood donors from the same age, sex and community area. C_LI

Symptomatic and asymptomatic transmission of SARS-CoV-2 in K-12 schools, British Columbia, April to June 2021 (preprint)

We prospectively studied SARS-CoV-2 transmission at schools in an era of Variants of Concern (VoCs), offering all close contacts serial viral asymptomatic testing up to 14 days. Of 229 school close contacts, 3 tested positive (1.3%), of which 2 were detected through asymptomatic testing. Most secondary transmission (90%) occurred in households. Routine asymptomatic testing of close contacts should be examined in the context of local testing rates, preventive measures, programmatic costs, and health impacts of asymptomatic transmission.

Performance of Immunoglobulin G Serology on Finger Prick Capillary Dried Blood Spot Samples to Measure SARS-CoV-2 Humoral Immunogenicity (preprint)

Abstract: Importance: Measuring humoral immunogenicity of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) vaccines and finding population-level correlates of protection against coronavirus disease (COVID-19) presents an immediate challenge to public health practitioners. Objective: To study the diagnostic accuracy and predictive value of finger prick capillary dried blood spot (DBS) samples tested using an anti-immunoglobulin G (IgG) serology assay to measure SARS-CoV-2 seropositivity and the humoral immunogenicity of COVID-19 vaccination. Design, Setting and Participants: This cross-sectional study enrolled participants (n= 644) who had paired DBS and serum samples collected by finger prick and venipuncture, respectively, in British Columbia, Canada between January 12th, 2020 and May 21st, 2021. Samples were tested by a multiplex electrochemiluminescence assay for SARS-CoV-2 anti-Spike (S), -Nucleocapsid (N) and -receptor binding domain (RBD) IgG reactivity using a Meso Scale Discovery (MSD) platform. Additionally, unpaired DBS samples (n= 6,706) that were collected in the province during the same time period were included for analysis of SARS-CoV-2 anti-N IgG reactivity. Exposure: Collection of a capillary DBS by finger prick alone or paired with serum by venipuncture. Outcome: Humoral immune response to SARS-CoV-2 measured by detection of anti-S, -N or -RBD IgG. Results: In comparison to a paired-serum reference, DBS samples possessed a sensitivity of 80% (95% CI: 61%-91%) and specificity of 97% (95% CI: 95%-98%). Receiver operator characteristic curve analysis (ROC) found that participant DBS samples tested for anti-SARS-CoV-2 IgG by MSD V-PLEX COVID-19 Coronavirus Panel 2 assay accurately classify SARS-CoV-2 seroconversion at an 88% percent rate, AUC= 88% (95% CI: 81%-96%). Modelling found that a DBS-based testing approach has a high positive predictive value (PPV) (98% [95% CI: 98%-99%]) in a theoretical population with seventy-five percent COVID-19 vaccine coverage. At lower vaccine coverages of fifteen and forty-five percent, the test's PPV decreased and the negative predictive value increased. Conclusion: We demonstrate that DBS samples, when tested using an electrochemiluminescence assay, provide a valid alternative to traditional venipuncture and should be considered to reliably detect SARS-CoV-2 seropositivity.

Intention to receive a COVID-19 vaccine: Results from a population-based survey in Canada (preprint)

BackgroundThe success of any COVID-19 vaccine program ultimately depends on high vaccine uptake. This study determined overall intention to receive a COVID-19 vaccine and identified factors that predict intentions to be vaccinated against COVID-19 in Canada, specifically in key priority groups identified by the American Committee on Immunization Practice (ACIP) and the National Advisory Committee on Immunization (NACI) for early immunization. MethodsIndividuals from research cohorts from the general population of British Columbia aged 25-69 were invited complete an online survey based on validated scales and theoretical frameworks to explore intention to receive a COVID-19 vaccine. Two multivariable logistic regression models were conducted to determine factors associated with intention to receive the COVID-19 vaccine. ResultsOf 4,948 respondents, 79.8% intended to receive a COVID-19 vaccine. In multivariable modeling, respondents who intended to receive the vaccine had higher vaccine attitudinal scores (p <0.001), reported greater influence of direct social norms (p = 0.001), and indirect social norms, including their family physician (p = 0.024), and Provincial Health Officer (p = 0.011). Older individuals (>60 years) were more likely to intend to receive the vaccine, while females (95%CI 0.57,0.93), those with less than high school education (95%CI 0.5,0.76), those who self-identified as non-white (95%CI 0.60,0.92), self-identified as Indigenous (95%CI 0.36,0.84) and essential non-health care workers (95%CI 0.59,0.86) had lower adjusted odds of intending to receive a COVID-19 vaccine. ConclusionsTo optimize vaccine coverage, public health should focus on key messages around vaccine safety and benefit, and leverage trusted practitioners for messaging. As certain key populations identified by NACI and ACIP for early immunization report a lower intention to vaccinate, there is a need for in-depth education and support for these communities to ensure optimal uptake.

Gargle-Direct: Extraction-Free Detection of SARS-CoV-2 using Real-time PCR (RT-qPCR) of Saline Gargle Rinse Samples (preprint)

Background: Saline mouth rinse/gargle samples have recently been shown to be a suitable option for swab-independent self-collection for SARS-CoV-2 diagnosis. We sought to evaluate a simplified process for direct reverse transcriptase PCR(RT-qPCR) testing of this novel sample type and to compare performance with routine RT-qPCR using automated nucleic acid extraction. Methods: Clinical saline mouth rinse/gargle samples were subjected to automated nucleic acid extraction (standard method), followed by RT-qPCR using three assays including the FDA authorized US-CDCs N1/N2 assay, which was the reference standard for determining sensitivity/specificity. For extraction-free workflow, an aliquot of each gargle sample underwent viral heat inactivation at 65 {degrees}C for 20 minutes followed by RT-qPCR testing, without an intermediate extraction step. An in-house validated RT-qPCR lab developed test (LDT), targeting the SARS-CoV-2, S/ORF8 genes (SORP triplex assay) and the N1/N2 US-CDC assay was used to evaluate the extraction-free protocol. To improve the analytical sensitivity, we developed a single-tube hemi-nested (STHN) version of the SORP triplex assay. Results: A total of 38 SARS-CoV-2 positive and 75 negative saline mouth rinse/gargle samples were included in this evaluation. A 100% concordance in detection rate was obtained between the standard method and the extraction-free approach for the SORP assay. An average increase of +2.63 to +5.74 of the cycle threshold (CT) values was observed for both the SORP and N1/N2 assay when extraction-free was compared between the standard method. The average {Delta}CT [({Delta}CT=CT(Direct PCR)-CT(Extracted RNA)], for each of the gene targets were: S ({Delta}CT= +4.24), ORF8 ({Delta}CT=+2.63), N1 ({Delta}CT=+2.74) and N2 ({Delta}CT=+5.74). The {Delta}CT for the STHN SORP assay was +1.51 and -2.05 for the S and ORF8 targets respectively, when extracted method was compared to the standard method. Conclusion: Our Gargle-Direct SARS-CoV-2 method is operationally simple, minimizes pre-analytical sample processing and is potentially implementable by most molecular diagnostic laboratories. The empirical demonstration of single-tube hemi-nested RT-qPCR, to specifically address and alleviate the widely-acknowledged problem of reduced analytical sensitivity of detection of extraction-free templates, should help diagnostic laboratories in choosing Gargle-Direct protocol for high-throughput testing.

Antibody reactivity to SARS-CoV-2 in adults from the Vancouver metropolitan area, Canada (preprint)

Background: Quantifying antibody reactivity to SARS-CoV-2 antigens may help understand its effect on COVID-19 severity at the population level. This antibody reactivity may be particularly prevalent among childcare providers, including pediatric health care workers (HCW) who may be more exposed to circulating coronaviruses. Methods: Cross-sectional study that included adults in the Vancouver area in British Columbia (BC), Canada, between May 17 and June 19, 2020. A novel 10-plex antibody assay (IgG) was used to measure antibody reactivity against the spike protein from circulating coronaviruses (229E, NL63, OC43, and HKU1), SARS-CoV, and four SARS-CoV-2 antigens. Seroreactivity from previous viral exposure was ascertained using this assay, and by measuring total SARS-CoV-2 IgG/M/A antibodies against a recombinant spike (S1) protein using a commercial CLIA assay. Findings: Among 276 participants (71% HCW), three showed evidence of direct viral exposure, yielding an adjusted seroprevalence of 0.6% [95%CI 0.2 to 3.1%], with no difference between HCW and non-HCW, or between paediatric and adult HCW. Among the remaining 273 unexposed individuals, 7.3% [95%CI 4.5% to 11.1%], 48.7 [95%CI 42.7% to 54.8%] and 82.4% [95%CI 77.4% to 86.7%] showed antibody reactivity against SARS-CoV-2 RBD, N or Spike proteins, respectively. This reactivity was evenly distributed as a function of age, sex or between paediatric and adult HCW, and partly correlated with reactivity to circulating coronaviruses (Spearman; range: 0.147 to 0.513 for significant correlation after false-discovery rate adjustment at 5%). Interpretation: A substantial proportion of individuals in this population showed antibody reactivity against SARS-CoV-2 antigens despite low serological evidence of SARS-CoV-2 exposure.

Self-collected Saline Gargle Samples as an Alternative to Healthcare Worker Collected Nasopharyngeal Swabs for COVID-19 Diagnosis in Outpatients (preprint)

Background: We assessed the performance, stability, and user acceptability of swab-independent self-collected saliva and saline mouth rinse/gargle sample types for the molecular detection of SARS-CoV-2 in adults and school-aged children. Methods: Outpatients who had recently been diagnosed with COVID-19 or were presenting with suspected COVID-19 were asked to have a nasopharyngeal swab collected and provide at least one self-collected sample type. A portion of participants were also asked about sample acceptability. Samples underwent molecular testing using multiple assays. Saline mouth rinse/gargle and saliva samples were tested daily at time zero, day one, and day 2 to assess nucleic acid stability at room temperature. Results: 50 participants (aged 4 to 71 years) were included; of these, 40 had at least one positive sample and were included in the primary sample yield analysis. Saline mouth rinse/gargle samples had a sensitivity of 98% (39/40) while saliva samples had a sensitivity of 79% (26/33). Both saline mouth rinse/gargle and saliva samples showed stable viral RNA detection after 2 days of room temperature storage. Mouth rinse/gargle samples had the highest (mean 4.9) and HCW-collected NP swabs had the lowest acceptability scores (mean 3.1). Conclusion: Saline mouth rinse/gargle samples demonstrated the highest combined user acceptability ratings and analytical performance when compared with saliva and HCW collected NP swabs. This sample type is a promising swab-independent option, particularly for outpatient self-collection in adults and school aged children.