Seroprevalence, seroconversion, and seroreversion of infection-induced SARS-CoV-2 antibodies among a cohort of children and adolescents in Montreal, Canada

ImportanceRepeated serological testing for SARS-CoV-2 allows the monitoring of antibody dynamics in populations, including detecting infections that are missed by RT-PCR or antigen testing. Understanding the factors associated with seroconversion and seroreversion as well as the duration of infection-induced antibodies can also inform public health recommendations regarding disease prevention and mitigation efforts. ObjectiveTo use serological testing to assess the prevalence, seroconversion, and seroreversion of infection-induced SARS-CoV-2 antibodies in children and adolescents in Montreal, Canada. DesignThis analysis reports on three rounds of data collection from a prospective cohort study (Enfants et COVID-19: Etude de seroprevalence [EnCORE]). The study rounds occurred as follows: Round 1 October 2020-March 2021, Round 2 May to July 2021, and Round 3 November 2021 to January 2022. Most Round 3 samples were collected prior to the spread of the Omicron BA.1 variant in Quebec. SettingPopulation-based sample. ParticipantsChildren and adolescents aged 2 to 17 years in Montreal, Canada. ExposurePotential exposure to SARS-CoV-2. Main Outcomes and MeasuresParticipants provided dried blood spots (DBS) for antibody detection and parents completed online questionnaires for sociodemographics and COVID-19 symptoms and testing history. The serostatus of participants was determined by enzyme-linked immunosorbent assays (ELISAs) using the receptor-binding domain (RBD) from the spike protein and the nucleocapsid protein (N) as antigens. We estimated seroprevalence for each round of data collection and by participant and household characteristics. Seroconversion rates were calculated as were the likelihoods of remaining seropositive at six months and one year. ResultsThe study included DBS samples from 1 632, 936, and 723 participants in the first, second, and third rounds of data collection, respectively. The baseline seroprevalence was 5{middle dot}8% (95% CI 4{middle dot}8-7{middle dot}1), which increased to 10{middle dot}5% and 10{middle dot}9% for the respective follow-ups (95% CI 8{middle dot}6-12{middle dot}7; 95% CI 8{middle dot}8-13{middle dot}5). The overall average crude rate of seroconversion over the study period was 12{middle dot}7 per 100 person-years (95% CI 10{middle dot}9-14{middle dot}5). Adjusted hazard rates of seroconversion by child and household characteristics showed higher rates in children who were female, whose parent identified as a racial or ethnic minority, and in households with incomes less than 100K. The likelihood of remaining seropositive at six months was 67% (95% CI 59-76) and dropped to 19% (95% CI 11%-33%) at one year. Conclusions and RelevanceThe data reported here provide estimates of pre-Omicron seroprevalence, seroconversion rates and time to seroreversion in a population-based cohort of children and adolescents. Serological studies continue to provide valuable contributions for infection prevalence estimates and help us better understand the dynamics of antibody levels following infection. Continued study of seroconversion and seroreversion can inform public health recommendations such as COVID-19 vaccination and booster schedules. KEY POINTSO_ST_ABSQuestionC_ST_ABSWhat was the rate of seroconversion and time to seroreversion for SARS-CoV-2 antibodies among children and adolescents in Montreal between October 2020 to January 2022? FindingsThe overall average crude rate of seroconversion was 12{middle dot}7 per 100 person-years (95% CI 10{middle dot}9-14{middle dot}5). We observed higher rates of seroconversion in children who were female, whose parent identified as a racial or ethnic minority, and in households with incomes less than 100K. Among all children who seroconverted, 71% had not been previously diagnosed with COVID-19. Median time to seroreversion was 7{middle dot}5 months. MeaningEven before the emergence of the Omicron variants, we observed a high rate of seroconversion for infection-induced SARS-CoV-2 antibodies along with widespread antibody waning by one year. Many children and adolescents seroconverted despite not receiving a prior COVID-19 diagnosis, indicating that RT-PCR and antigen testing continue to underestimate true disease prevalence.

The changing landscape of respiratory viruses contributing to respiratory hospitalisations: results from a hospital-based surveillance in Quebec, Canada, 2012-13 to 2021-22

BackgroundA comprehensive description of the combined effect of SARS-CoV-2 and respiratory viruses (RV) other than SARS-CoV-2 (ORV) on hospitalisations is lacking. AimTo compare viral etiology of acute respiratory infections (ARI) hospitalisations before and during two pandemic years from a surveillance network in Quebec, Canada. MethodWe compared detection of ORV and SARS-CoV-2 during 2020-21 and 2021-22 to 8 pre-pandemic influenza seasons in patients hospitalised with ARI who were tested systematically by a multiplex PCR. ResultsDuring pre-pandemic influenza seasons, overall RV detection was 92.7% (1,493) (48.3% respiratory syncytial virus (RSV)) in children and 62.8% (4,339) (40.1% influenza) in adults. Overall RV detection in 2020-21 was 58.6% (29) in children (all ORV) and 43.7% (333) in adults (3.4% ORV, 40.3% SARS-CoV2, both including coinfections). In 2021-22 overall RV detection was 91.0% (201) in children (82.8% ORV, 8.1% SARS-CoV-2, both including coinfections) and 55.5% (527) in adults (14.1% ORV, 41.4% SARS-CoV-2, both including coinfections). Virtually no influenza was detected in 2020-21 and in 2021-22 up to epi-week 2022-9 presented here; no RSV was detected in 2020-21. In 2021-22, detection of RSV was comparable to pre-pandemic years but with an unusually early season. There were significant differences in ORV and SARS-CoV-2 detection between time periods and age groups. ConclusionSignificant continuous shifts in age distribution and viral etiology of ARI hospitalisations occurred during two pandemic years. This reflects evolving RV epidemiology and underscores the need for increased scrutiny of ARI hospitalisation etiology to inform tailored public health recommendations.

Immunogenicity of Pfizer-BioNTech COVID-19 mRNA Primary Vaccination Series in Recovered Individuals Depends on Symptoms at Initial Infection.

ImportancePublic health vaccination recommendations for COVID-19 primary series and boosters in previously infected individuals differ worldwide. As infection with SARS-CoV-2 is often asymptomatic, it remains to be determined if vaccine immunogenicity is comparable in all previously infected subjects. We present detailed immunological evidence to clarify the requirements for one-or two-dose primary vaccination series for naturally primed individuals. ObjectiveEvaluate the immune response to COVID-19 mRNA vaccines in healthcare workers (HCWs) who recovered from a SARS-CoV-2 infection. DesignMulticentric observational prospective cohort study of HCWs with a PCR-confirmed SARS-CoV-2 infection designed to evaluate the dynamics of T and B cells immune responses to primary infection and COVID-19 mRNA vaccination over 12 months. ParticipantsUnvaccinated HCWs with PCR-confirmed SARS-CoV-2 infection were selected based on the presence or absence of symptoms at infection and serostatus at enrollment. Age- and sex-matched adults not infected with SARS-CoV-2 prior to vaccination were included as naive controls. ExposureVaccination with Pfizer BioNTech BNT162b2 mRNA vaccine. Main Outcome(s) and Measure(s)Immunity score (zero to three), before and after vaccination, based on anti-RBD IgG ratio, serum capacity to neutralize live virus and IFN-{gamma} secretion capacity in response to SARS-CoV-2 peptide pools above the positivity threshold for each of the three assays. We compared the immunity score between groups based on subjects symptoms at diagnosis and/or serostatus prior to vaccination. ResultsNone of the naive participants (n=14) showed a maximal immunity score of three following one dose of vaccine compared to 84% of the previously infected participants (n=55). All recovered individuals who did not have an immunity score of three were seronegative prior to vaccination, and 67% had not reported symptoms resulting from their initial infection. Following one dose of vaccine, their immune responses were comparable to naive individuals, with significantly weaker responses than those who were symptomatic during infection. Conclusions and RelevanceIndividuals who did not develop symptoms during their initial SARS-CoV-2 infection and were seronegative prior to vaccination present immune responses comparable to that of naive individuals. These findings highlight the importance of administering the complete two-dose primary regimen and following boosters of mRNA vaccines to individuals who experienced asymptomatic SARS-CoV-2 infection. KEY POINTS QuestionIs a single dose of COVID-19 mRNA vaccine sufficient to induce robust immune responses in individuals with prior SARS-CoV-2 infection? FindingsIn this cohort of 55 health care workers previously infected with SARS-CoV-2, we show that the absence of symptoms during initial infection and negative serostatus prior to vaccination predict the strength of immune responses to COVID-19 mRNA vaccine. Lack of symptoms and a negative serostatus prior to vaccination leads to immune responses comparable to naive individuals. MeaningOur results support a two-dose primary series requirement for any individual with prior history of asymptomatic SARS-CoV-2 infection.

In Vitro Selection of Remdesivir-Resistant SARS-CoV-2 Demonstrates High Barrier to Resistance.

In vitro selection of remdesivir-resistant SARS-CoV-2 revealed the emergence of a V166L substitution, located outside of the polymerase active site of the nsp12 protein, after 9 passages. V166L remained the only nsp12 substitution after 17 passages at a final concentration of 10 {micro}M RDV, conferring a 2.3-fold increase in EC50. When V166L was introduced into a recombinant SARS-CoV-2 virus, a 1.5-fold increase in EC50 was observed, indicating a high in vitro barrier to RDV resistance.

The REinfection in COVID-19 Estimation of Risk (RECOVER) study: Reinfection and serology dynamics in a cohort of Canadian healthcare workers.

BackgroundUnderstanding the immune response to natural infection by SARS-CoV-2 is key to pandemic management, especially in the current context of emerging variants. Uncertainty remains regarding the efficacy and duration of natural immunity against reinfection. MethodWe conducted an observational prospective cohort study in Canadian healthcare workers (HCWs) with a history of PCR-confirmed SARS-CoV-2 infection to : (i) measure the average incidence rate of reinfection and (ii), describe the serological immune response to the primary infection. ResultsWe detected 5 cases of reinfection over 14 months of follow-up, for a reinfection incidence rate of 3.3 per 100 person-years. Median duration of seropositivity was 420 days in symptomatics at primary infection compared to 213 days in asymptomatics (p<0.0001). Other variables associated with prolonged seropositivity for IgG against the spike protein included age 55 and above, obesity, and non-Caucasian ethnicity. SummaryAmong healthcare workers, the incidence of reinfection with SARS-CoV-2 following a primary infection remained rare, although our analysis predates the circulation of the Omicron variant.

Impact of temperature on the affinity of SARS-CoV-2 Spike for ACE2

The seasonal nature in the outbreaks of respiratory viral infections with increased transmission during low temperatures has been well established. The current COVID-19 pandemic makes no exception, and temperature has been suggested to play a role on the viability and transmissibility of SARS-CoV-2. The receptor binding domain (RBD) of the Spike glycoprotein binds to the angiotensin-converting enzyme 2 (ACE2) to initiate viral fusion. Studying the effect of temperature on the receptor-Spike interaction, we observed a significant and stepwise increase in RBD-ACE2 affinity at low temperatures, resulting in slower dissociation kinetics. This translated into enhanced interaction of the full Spike to ACE2 receptor and higher viral attachment at low temperatures. Interestingly, the RBD N501Y mutation, present in emerging variants of concern (VOCs) that are fueling the pandemic worldwide, bypassed this requirement. This data suggests that the acquisition of N501Y reflects an adaptation to warmer climates, a hypothesis that remains to be tested.

Seroprevalence of anti-SARS-CoV-2 antibodies among school and daycare children and personnel: Protocol for a cohort study in Montreal, Canada

BackgroundFurther evidence is needed to understand the contribution of schools and daycares to the spread of COVID-19 in the context of diverse transmission dynamics and continually evolving public health interventions. The Enfants et COVID-19: Etude de seroprevalence (EnCORE) study will estimate the seroprevalence and seroconversion of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) among school and daycare children and personnel. In addition, the study will examine associations between seroprevalence and socio-demographic characteristics and reported COVID-19 symptoms and tests, and investigates changes in health, lifestyle and well-being outcomes. MethodsThis study includes children and personnel from 62 schools and daycares in four neighbourhoods in Montreal, Canada. All children age 2-17 years attending one of the participating schools or daycares and their parents are invited to participate, as well as a sample of personnel members. Participants respond to brief questionnaires and provide blood samples, collected via dried blood spot (DBS), at baseline (October 2020-March 2021) and follow-up (May-June 2021). Questionnaires include socio-demographic and household characteristics, reported COVID-19 symptoms and tests, potential COVID-19 risk factors and prevention efforts, and health and lifestyle information. Logistic regression using generalized estimating equations will be used to estimate seroprevalence and seroconversion, accounting for school-level clustering. DiscussionThe results of the EnCORE study will contribute to our knowledge about SARS-CoV-2 transmission in schools and daycares, which is critical for decisions regarding school attendance and the management of school outbreaks through the remainder of this school year and beyond.

Genetics of symptom remission in outpatients with COVID-19

We conducted a genome-wide association study of time to remission of COVID-19 symptoms in 1723 outpatients with at least one risk factor for disease severity from the COLCORONA clinical trial. We found a significant association at 5p13.3 (rs1173773; P = 4.94 x 10-8) near the natriuretic peptide receptor 3 gene (NPR3). By day 15 of the study, 44%, 54% and 59% of participants with 0, 1, or 2 copies of the effect allele respectively, had symptom remission. In 851 participants not treated with colchicine (placebo), there was a significant association at 9q33.1 (rs62575331; P = 2.95 x 10-8) in interaction with colchicine (P = 1.19 x 10-5) without impact on risk of hospitalisations, highlighting a possibly shared mechanistic pathway. By day 15 of the study, 46%, 62% and 64% of those with 0, 1, or 2 copies of the effect allele respectively, had symptom remission. The findings need to be replicated and could contribute to the biological understanding of COVID-19 symptom remission.

Efficacy of Colchicine in Non-Hospitalized Patients with COVID-19

BackgroundEvidence suggests the role of an inflammatory storm in COVID-19 complications. Colchicine is an orally administered, anti-inflammatory medication beneficial in gout, pericarditis and coronary disease. MethodsWe performed a randomized, double-blind trial involving non-hospitalized patients with COVID-19 diagnosed by polymerase chain reaction (PCR) testing or clinical criteria. The patients were randomly assigned to receive colchicine (0.5 mg twice daily for 3 days and once daily thereafter) or placebo for 30 days. The primary efficacy endpoint was the composite of death or hospitalization for COVID-19. ResultsA total of 4488 patients were enrolled. The primary endpoint occurred in 4.7% of the patients in the colchicine group and 5.8% of those in the placebo group (odds ratio, 0.79; 95.1% confidence interval (CI), 0.61 to 1.03; P=0.08). Among the 4159 patients with PCR-confirmed COVID-19, the primary endpoint occurred in 4.6% and 6.0% of patients in the colchicine and placebo groups, respectively (odds ratio, 0.75; 95% CI, 0.57 to 0.99; P=0.04). In these patients with PCR-confirmed COVID-19, the odds ratios were 0.75 (95% CI, 0.57 to 0.99) for hospitalization due to COVID-19, 0.50 (95% CI, 0.23 to 1.07) for mechanical ventilation, and 0.56 (95% CI, 0.19 to 1.66) for death. Serious adverse events were reported in 4.9% and 6.3% in the colchicine and placebo groups (P=0.05); pneumonia occurred in 2.9% and 4.1% of patients (P=0.02). Diarrhea was reported in 13.7% and 7.3% in the colchicine and placebo groups (P<0.0001). ConclusionAmong non-hospitalized patients with COVID-19, colchicine reduces the composite rate of death or hospitalization. (COLCORONA ClinicalTrials.gov number: NCT04322682)