Medicare Skilled Nursing Facility Use and Spending Before and After Introduction of the Public Health Emergency Waiver During the COVID-19 Pandemic.

Importance: In response to the COVID-19 pandemic, Medicare introduced a public health emergency (PHE) waiver in March 2020, removing a 3-day hospitalization requirement before fee-for-service beneficiaries could receive skilled nursing facility (SNF) care benefits. Objective: To assess whether there were changes in SNF episode volume and Medicare spending on SNF care before and during the PHE among long-term care (LTC) residents and other Medicare beneficiaries. Design, Setting, and Participants: This retrospective cohort study used Medicare fee-for-service claims and the Minimum Data Set for Medicare beneficiaries who were reimbursed for SNF care episodes from January 2018 to September 2021 in US SNFs. Exposures: The prepandemic period (January 2018-February 2020) vs the PHE period (March 2020-September 2021). Main Outcomes and Measures: The main outcomes were SNF episode volume, characteristics, and costs. Episodes were defined as standard (with a preceding 3-day hospitalization) or waiver (with other or no acute care use). Results: Skilled nursing facility care was provided to 4 299 863 Medicare fee-for-service beneficiaries. Medicare beneficiaries had on average 130 400 monthly SNF episodes in the prepandemic period (mean [SD] age of beneficiaries, 78.9 [11.0] years; 59% female) and 108 575 monthly episodes in the PHE period (mean [SD] age of beneficiaries, 79.0 [11.1] years; 59% female). All waiver episodes increased from 6% to 32%, and waiver episodes without preceding acute care increased from 3% to 18% (from 4% to 49% among LTC residents). Skilled nursing facility episodes provided for LTC residents increased by 77% (from 15 538 to 27 537 monthly episodes), primarily due to waiver episodes provided for residents with COVID-19 in 2020 and early 2021 (62% of waiver episodes without preceding acute care). Skilled nursing facilities in the top quartile of waiver episodes were more often for-profit (80% vs 68%) and had lower quality ratings (mean [SD] overall star rating, 2.7 [1.4] vs 3.2 [1.4]; mean [SD] staffing star rating, 2.5 [1.1] vs 3.0 [1.2]) compared with SNFs in the other quartiles. Monthly Medicare spending on SNF care was $2.1 billion before the pandemic and $2.0 billion during the PHE. For LTC residents, monthly SNF spending increased from $301 million to $585 million while spending on hospitalizations remained relatively stable. Conclusions and Relevance: This cohort study found that the PHE waiver for SNF care was associated with a marked increase in the prevalence of SNF episodes without a preceding hospitalization, especially in the first year of the COVID-19 pandemic. The waiver was used primarily among certain types of facilities and for LTC residents with COVID-19. Although the effect of the waiver cannot be differentiated from that of the pandemic, overall SNF care costs did not increase substantially; for LTC residents, the waiver was applied primarily for COVID-19 care, suggesting the waiver's successful implementation.

Changes in socioeconomic resources and mental health after the second COVID-19 wave (2020-2021): a longitudinal study in Switzerland.

BACKGROUND: During the 2020/2021 winter, the labour market was under the impact of the COVID-19 pandemic. Changes in socioeconomic resources during this period could have influenced individual mental health. This association may have been mitigated or exacerbated by subjective risk perceptions, such as perceived risk of getting infected with SARS-CoV-2 or perception of the national economic situation. Therefore, we aimed to determine if changes in financial resources and employment situation during and after the second COVID-19 wave were prospectively associated with depression, anxiety and stress, and whether perceptions of the national economic situation and of the risk of getting infected modified this association. METHODS: One thousand seven hundred fifty nine participants from a nation-wide population-based eCohort in Switzerland were followed between November 2020 and September 2021. Financial resources and employment status were assessed twice (Nov2020-Mar2021, May-Jul 2021). Mental health was assessed after the second measurement of financial resources and employment status, using the Depression, Anxiety and Stress Scale (DASS-21). We modelled DASS-21 scores with linear regression, adjusting for demographics, health status, social relationships and changes in workload, and tested interactions with subjective risk perceptions. RESULTS: We observed scores above thresholds for normal levels for 16% (95%CI = 15-18) of participants for depression, 8% (95%CI = 7-10) for anxiety, and 10% (95%CI = 9-12) for stress. Compared to continuously comfortable or sufficient financial resources, continuously precarious or insufficient resources were associated with worse scores for all outcomes. Increased financial resources were associated with higher anxiety. In the working-age group, shifting from full to part-time employment was associated with higher stress and anxiety. Perceiving the Swiss economic situation as worrisome was associated with higher anxiety in participants who lost financial resources or had continuously precarious or insufficient resources. CONCLUSION: This study confirms the association of economic stressors and mental health during the COVID-19 pandemic and highlights the exacerbating role of subjective risk perception on this association.

Lifestyle Behaviours of Children and Adolescents During the First Two Waves of the COVID-19 Pandemic in Switzerland and Their Relation to Well-Being: An Observational Study.

Objectives: To describe changes in adherence to recommendations for physical activity (PA), screen time (ST), and sleep duration over the first two waves of the pandemic in Switzerland, and to assess the associations of these lifestyle behaviours with life satisfaction and overall health as well-being indicators. Methods: In this observational study, we included 2,534 participants (5-16 years) from four Swiss cantons. Participants, or their parents, completed repeated questionnaires and reported on their (child's) lifestyle and well-being, between June 2020 and April 2021. We used linear and logistic regression models to assess the associations between lifestyle and well-being. Results: The percentage of children meeting the recommendations for PA and ST decreased from the pre-pandemic period to the first wave, with a slight recovery during the second wave. Participants meeting all three recommendations during the second wave were more likely to report excellent health (OR: 1.65 [95% CI: 1.00-2.76]) and higher life satisfaction (ß: 0.46 [0.16-0.77]) in early 2021 than participants not meeting any recommendation. Conclusion: We showed a substantial impact of the COVID-19 pandemic on children's and adolescents' lifestyle, and a positive association between meeting lifestyle recommendations and well-being.

Heterogeneous evolution of SARS-CoV-2 seroprevalence in school-age children: Results from the school-based cohort study Ciao Corona in November-December 2021 in the canton of Zurich.

BACKGROUND: Much remains unknown regarding the evolution of SARS-CoV-2 seroprevalence and variability in seropositive children in districts, schools and classes as only a few school-based cohort studies exist. Vaccination of children, initiated at different times for different age groups, adds additional complexity to the understanding of how seroprevalence developed in the school aged population. AIM: We investigated the evolution of SARS-CoV-2 seroprevalence in children and its variability in districts, schools and classes in Switzerland from June/July 2020 to November/December 2021. METHODS: In this school-based cohort study, SARS-CoV-2 antibodies were measured in primary and secondary school children from randomly selected schools in the canton of Zurich in October/November 2020, March/April 2021 and November/December 2021. Seroprevalence was estimated using Bayesian logistic regression to adjust for test sensitivity and specificity. Variability of seroprevalence between school classes was expressed as maximum minus minimum seroprevalence in a class and summarised as median (interquartile range). RESULTS: 1875 children from 287 classes in 43 schools were tested, with median age 12 years (range 6-17), 51% 12+ vaccinated. Seroprevalence increased from 5.6% (95% credible interval [CrI] 3.5-7.6%) to 31.1% (95% CrI 27.0-36.1%) in unvaccinated children, and 46.4% (95% CrI 42.6-50.9%) in all children (including vaccinated). Earlier in the pandemic, seropositivity rates in primary schools were similar to or slightly higher (<5%) than those in secondary schools, but by late 2021, primary schools had 12.3% (44.3%) lower seroprevalence for unvaccinated (all) subjects. Variability in seroprevalence among districts and schools increased more than two-fold over time, and in classes from 11% (95% CrI 7-17%) to 40% (95% CrI 22-49%). CONCLUSIONS: Seroprevalence in children increased greatly, especially in 2021 following introduction of vaccines. Variability in seroprevalence was high and increased substantially over time, suggesting complex transmission chains.

Evolution of SARS-CoV-2 seroprevalence and clusters in school children from June 2020 to April 2021: prospective cohort study Ciao Corona.

BACKGROUND: Few studies have explored the spread of SARS-CoV-2 in schools in 2021, with the advent of variants of concern. We aimed to examine the evolution of the proportion of seropositive children at schools from June-July 2020 to March-April 2021. We also examined symptoms, under-detection of infections, potential preventive effect of face masks, and reasons for non-participation in the study. METHODS: Children in lower (7­10 years), middle (8­13 years) and upper (12­17 years) school levels in randomly selected schools and classes in the canton of Zurich, Switzerland, were invited to participate in the prospective cohort study Ciao Corona. Three testing rounds were completed in June-July 2020, October-November 2020 and March-April 2021. From 5230 invited, 2974 children from 275 classes in in 55 schools participated in at least one testing round. We measured SARS-CoV-2 serology in venous blood, and parents filled in questionnaires on sociodemographic information and symptoms. RESULTS: The proportion of children seropositive for SARS-CoV-2 increased from 1.5% (95% credible interval [CrI] 0.6­2.6%) by June-July 2020, to 6.6% (4.0­8.9%) by October-November, and to 16.4% (12.1­19.5%) by March-April 2021. By March-April 2021, children in upper school level (12.4%; 7.3­16.7%) were less likely to be seropositive than those in middle (19.5%; 14.2­24.4%) or lower school levels (16.0%; 11.0­20.4%). The ratio of PCR-diagnosed to all seropositive children changed from one to 21.7 (by June-July 2020) to one to 3.5 (by March-April 2021). Potential clusters of three or more newly seropositive children were detected in 24 of 119 (20%) classes, 17 from which could be expected by chance. Clustering was not higher than expected by chance in middle and upper school levels. Children in the upper school level, who were wearing face masks at school from November 2020, had a 5.1% (95% confidence interval 9.4% to 0.7%) lower than expected seroprevalence by March-April 2021 than those in middle school level, based on difference-in-differences analysis. Symptoms were reported by 37% of newly seropositive and 16% seronegative children. Fear of blood sampling (64%) was the most frequently reported reason for non-participation. CONCLUSIONS: Although the proportion of seropositive children increased from 1.5% in June-July 2020 to 16.4% in March-April 2021, few infections were likely associated with potential spread within schools. In March-April 2021, significant clustering of seropositive children within classes was observed only in the lower school level.

Lifestyle Behaviours of Children and Adolescents During the First Two Waves of the COVID-19 Pandemic in Switzerland and Their Relation to Well-Being: An Observational Study

Objectives: To describe changes in adherence to recommendations for physical activity (PA), screen time (ST), and sleep duration over the first two waves of the pandemic in Switzerland, and to assess the associations of these lifestyle behaviours with life satisfaction and overall health as well-being indicators. Methods: In this observational study, we included 2,534 participants (5–16 years) from four Swiss cantons. Participants, or their parents, completed repeated questionnaires and reported on their (child’s) lifestyle and well-being, between June 2020 and April 2021. We used linear and logistic regression models to assess the associations between lifestyle and well-being. Results: The percentage of children meeting the recommendations for PA and ST decreased from the pre-pandemic period to the first wave, with a slight recovery during the second wave. Participants meeting all three recommendations during the second wave were more likely to report excellent health (OR: 1.65 [95% CI: 1.00–2.76]) and higher life satisfaction (β: 0.46 [0.16–0.77]) in early 2021 than participants not meeting any recommendation. Conclusion: We showed a substantial impact of the COVID-19 pandemic on children’s and adolescents’ lifestyle, and a positive association between meeting lifestyle recommendations and well-being.

Parents' Working Conditions in the Early COVID-19 Pandemic and Children's Health-Related Quality of Life: The Ciao Corona Study.

Objective: To assess the associations between parents' working conditions during the lockdown period (March-May 2020) and children's health-related quality of life (HRQOL) over the first year of the COVID-19 pandemic in Zurich, Switzerland. Methods: We included 2211 children (6-16 years) and their parents from the prospective study Ciao Corona. Parents reported their employment status and working conditions during the lockdown. Children's HRQOL was assessed in June-July 2020, January and March 2021 using the parents-report of the KINDL®. We used mixed models to assess the associations between parents' working conditions and children's HRQOL at the three time points. Results: Children from families in which at least one parent changed their working conditions during the lockdown showed lower HRQOL in June-July 2020, than children from families in which neither parent experienced changes. Children from families in which at least one parent had to work remotely continued to show lower HRQOL in January and March 2021. Conclusion: Changes in parents' working conditions during lockdown were negatively associated with children's HRQOL. Public health policies aiming to support families susceptible to adverse changes are needed.

SARS-CoV-2 seroprevalence in children, parents and school personnel from June 2020 to April 2021: cohort study of 55 schools in Switzerland.

BACKGROUND: Few studies have directly examined the incidence or seroprevalence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections in children, parents and teachers from the same school communities. This study aimed to describe SARS-CoV-2 seroprevalence within cantonal districts and school communities in children, parents and school personnel in June-September 2020 and March-April 2021 in the canton of Zürich, Switzerland. METHODS: We invited children from 55 randomly selected primary and secondary schools and 275 classes within them to participate in the Ciao Corona study in June-July 2020. Parents of the participating children and all school personnel were invited in August-September 2020. Eligible classes, parents and school personnel were tested again in March-April 2021. Venous blood was tested for SARS-CoV-2 serology. We collected sociodemographic information of the participants in online questionnaires on enrolment in the study. We excluded vaccinated adults and those with unverified vaccination status from the main analysis. Seroprevalence estimates were adjusted for test accuracy. We assessed the variability of seroprevalence within and across cantonal districts and school communities and compared it with the per capita cumulative incidence of confirmed SARS-CoV-2 infections. RESULTS: In June-September 2020, 2,473 children, 1,608 school personnel and 2,045 parents participated in the study. In June-September 2020, seroprevalence was low (4.4% to 5.8%) in all cohorts. In March-April 2021, seroprevalence in children and parents (18.1% and 20.9%) was slightly higher than in school personnel (16.9%). We observed a large variation in seroprevalence estimates of the three cohorts within and between districts and school communities, with the median ratio of children's seroprevalence to per capita confirmed cases in district inhabitants of 3.1 (interquartile range 2.6 to 3.9). Seroprevalence was lower in children in the upper school level and their parents, but not teachers. Children's seroprevalence was slightly higher in classes with infected main teachers and families with one infected parent and substantially higher in families with two infected parents. CONCLUSIONS: We observed similar seroprevalence in children and parents, somewhat lower in school personnel in March-April 2021 and striking variation between districts and school communities. Children's seroprevalence was higher in classes with infected main teachers and from families with infected parents.

Megatrends in Healthcare: Review for the Swiss National Science Foundation's National Research Programme 74 (NRP74) "Smarter Health Care".

Objectives: In this paper, we present a review of some relevant megatrends in healthcare conducted as part of the Swiss National Science Foundation's National Research Programme 74 (NRP74) "Smarter Health Care." Our aim is to stimulate discussions about long-term tendencies underlying the current and future development of the healthcare system. Methods: Our team-a multidisciplinary panel of researchers involved in the NRP74-went through an iterative process of internal consultations followed by a rapid literature review with the goal of reaching group consensus concerning the most relevant megatrends in healthcare. Results: Five megatrends were identified, namely: 1) Socio-demographic shifts. 2) Broadening meaning of "health." 3) Empowered patients and service users. 4) Digitalization in healthcare. 5) Emergence of new models of care. The main features of each megatrend are presented, drawing often on the situation in Switzerland as a paradigmatic example and adding reflections on the potential influence of the COVID-19 pandemic on them. Conclusion: Considering the long-term megatrends affecting the evolution of healthcare is important-amongst other things-to understand and contextualise the relevance and implications of innovative health services research results.

Perceptions towards mask use in school children during the SARS-CoV-2 pandemic: descriptive results from the longitudinal Ciao Corona cohort study.

BACKGROUND: Mask wearing contributes to the reduction of transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). In Switzerland, compulsory use of masks was introduced in indoor public spaces and later in schools. This study explored perceptions of the usefulness of masks in school and public in a cohort of children and adolescents in the canton of Zurich, Switzerland, in January to May 2021. METHODS: School children aged 10 to 17 years enrolled in Ciao Corona, a prospective school-based cohort study, responded to nested online surveys between 12 January and 24 March 2021 (Q1) and 10 March and 16 May 2021 (Q2). Secondary school children were surveyed at Q1 and Q2, and primary school children at Q2 only. Surveys for parents and their children included questions on the children's perception of the usefulness of masks and mask wearing behaviour by applying a non-validated questionnaire. Associations between perceived usefulness of masks and child's school level and gender, and parents' educational attainment were analysed with Pearson's and McNemar's chi-square tests. Free-text comments provided by children were classified into categories of expressed attitude towards mask wearing. RESULTS: A total of 595 (54% girls) and 1118 (52% girls) school children with predominantly Swiss nationality and a high socioeconomic status responded to online questionnaires at Q1 and Q2, respectively. More than half of the school children perceived masks to be useful at school (Q1: 60% and Q2: 57%) and in public (Q1: 69% and Q2 :60%). Girls perceived masks as useful more often than boys (at Q2 at school: 61% versus 53%, in public: 64% versus 57%), and children of parents with high educational attainment more often than those of parents with lower educational attainment (at Q2 at school: 61% versus 49%, in public: 63% versus 54%). At Q1 and Q2 each, about 20% of children provided individual statements about masks, of which 36% at Q1 and 16% at Q2 reported side effects and discomfort such as skin irritations, headache or difficulties breathing during physical education. CONCLUSIONS: Approximately 60% of school children perceived masks at school and in public places as useful. A small but non-negligible proportion of children reported discomfort and side effects that should be considered to ensure high adherence to mask wearing among school children. A validation of the questionnaire is needed.

Prediction of Past SARS-CoV-2 Infections: A Prospective Cohort Study Among Swiss Schoolchildren.

Objective: To assess the predictive value of symptoms, sociodemographic characteristics, and SARS-CoV-2 exposure in household, school, and community setting for SARS-CoV-2 seropositivity in Swiss schoolchildren at two time points in 2020. Design: Serological testing of children in primary and secondary schools (aged 6-13 and 12-16 years, respectively) took place in June-July (T1) and October-November (T2) 2020, as part of the longitudinal, school-based study Ciao Corona in the canton of Zurich, Switzerland. Information on sociodemographic characteristics and clinical history was collected with questionnaires to parents; information on school-level SARS-CoV-2 infections was collected with questionnaires to school principals. Community-level cumulative incidence was obtained from official statistics. We used logistic regression to identify individual predictors of seropositivity and assessed the predictive performance of symptom- and exposure-based prediction models. Results: A total of 2,496 children (74 seropositive) at T1 and 2,152 children (109 seropositive) at T2 were included. Except for anosmia (odds ratio 15.4, 95% confidence interval [3.4-70.7]) and headache (2.0 [1.03-3.9]) at T2, none of the individual symptoms were significantly predictive of seropositivity at either time point. Of all the exposure variables, a reported SARS-CoV-2 case in the household was the strongest predictor for seropositivity at T1 (12.4 [5.8-26.7]) and T2 (10.8 [4.5-25.8]). At both time points, area under the receiver operating characteristic curve was greater for exposure-based (T1, 0.69; T2, 0.64) than symptom-based prediction models (T1, 0.59; T2, 0.57). Conclusions: In children, retrospective identification of past SARS-CoV-2 infections based on symptoms is imprecise. SARS-CoV-2 seropositivity is better predicted by factors of SARS-CoV-2 exposure, especially reported SARS-CoV-2 cases in the household. Predicting SARS-CoV-2 seropositivity in children in general is challenging, as few reliable predictors could be identified. For an accurate retrospective identification of SARS-CoV-2 infections in children, serological tests are likely indispensable. Trial registration number: NCT04448717.

Variation in SARS-CoV-2 seroprevalence across districts, schools and classes: baseline measurements from a cohort of primary and secondary school children in Switzerland.

OBJECTIVES: To determine the variation in SARS-CoV-2 seroprevalence in school children and the relationship with self-reported symptoms. DESIGN: Baseline measurements of a longitudinal cohort study (Ciao Corona) from June to July 2020. SETTING: 55 schools stratified by district in the canton of Zurich, Switzerland. PARTICIPANTS: 2585 children (1339 girls; median age: 11 years, age range: 6-16 years), attending grades 1-2, 4-5 and 7-8. MAIN OUTCOME MEASURES: Variation in seroprevalence of SARS-CoV-2 in children across 12 cantonal districts, schools and grades, assessed using Luminex-based test of four epitopes for IgG, IgA and IgM (Antibody Coronavirus Assay,ABCORA 2.0). Clustering of cases within classes. Association of seropositivity and symptoms. Comparison with seroprevalence in adult population, assessed using Luminex-based test of IgG and IgA (Sensitive Anti-SARS-CoV-2 Spike Trimer Immunoglobulin Serological test). RESULTS: Overall seroprevalence was 2.8% (95% CI 1.5% to 4.1%), ranging from 1.0% to 4.5% across districts. Seroprevalence in grades 1-2 was 3.8% (95% CI 2.0% to 6.1%), in grades 4-5 was 2.4% (95% CI 1.1% to 4.2%) and in grades 7-8 was 1.5% (95% CI 0.5% to 3.0%). At least one seropositive child was present in 36 of 55 (65%) schools and in 44 (34%) of 131 classes where ≥5 children and ≥50% of children within the class were tested. 73% of children reported COVID-19-compatible symptoms since January 2020, with the same frequency in seropositive and seronegative children for all symptoms. Seroprevalence of children and adults was similar (3.2%, 95% credible interval (CrI) 1.7% to 5.0% vs 3.6%, 95% CrI 1.7% to 5.4%). The ratio of confirmed SARS-CoV-2 cumulative incidence-to-seropositive cases was 1:89 in children and 1:12 in adults. CONCLUSIONS: SARS-CoV-2 seroprevalence was low in children and similar to that in adults by the end of June 2020. Very low ratio of diagnosed-to-seropositive children was observed. We did not detect clustering of SARS-CoV-2-seropositive children within classes, but the follow-up of this study will shed more light on transmission within schools. TRIAL REGISTRATION NUMBER: NCT04448717.

Surveillance of Acute SARS-CoV-2 Infections in School Children and Point-Prevalence During a Time of High Community Transmission in Switzerland.

Background: Switzerland had one of the highest incidence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections in Europe during the second wave. Schools were open as in most of Europe with specific preventive measures in place. However, the frequency and transmission of acute unrecognized, asymptomatic or oligosymptomatic infections in schools during this time of high community transmission is unknown. Thereof, our aim was to pilot a surveillance system that detects acute SARS-CoV-2 infections in schools and possible transmission within classes. Methods: Fourteen out of the randomly selected sample of the Ciao Corona cohort study participated between December 1 and 11, a time when incidence rate for SARS-CoV-2 infections was high for the canton of Zurich. We determined point-prevalence of acute SARS-CoV-2 infections of school children attending primary and secondary school. A buccal swab for polymerase chain reaction (PCR) and a rapid diagnostic test (RDT) to detect SARS-CoV-2 were taken twice 1 week apart (T1 and T2) in a cohort of children from randomly selected classes. A questionnaire assessed demographics and symptoms compatible with a SARS-CoV-2 infection during the past 5 days. Results: Out of 1,299 invited children, 641 (49%) 6- to 16-year-old children and 66 teachers from 14 schools and 67 classes participated in at least one of two testings. None of the teachers but one child had a positive PCR at T1, corresponding to a point-prevalence in children of 0.2% (95% CI 0.0-1.1%), and no positive PCR was detected at T2. The child with positive PCR at T1 was negative on the RDT at T1 and both tests were negative at T2. There were 7 (0.6%) false positive RDTs in children and 2 (1.7%) false positive RDTs in teachers at T1 or T2 among 5 schools (overall prevalence 0.7%). All 9 initially positive RDTs were negative in a new buccal sample taken 2 h to 2 days later, also confirmed by PCR. Thirty-five percent of children and 8% of teachers reported mild symptoms during the 5 days prior to testing. Conclusion: In a setting of high incidence of SARS-CoV-2 infections, unrecognized virus spread within schools was very low. Schools appear to be safe with the protective measures in place (e.g., clearly symptomatic children have to stay at home, prompt contact tracing with individual and class-level quarantine, and structured infection prevention measures in school). Specificity of the RDT was within the lower boundary of performance and needs further evaluation for its use in schools. Given the low point prevalence even in a setting of very high incidence, a targeted test, track, isolate and quarantine (TTIQ) strategy for symptomatic children and school personnel adapted to school settings is likely more suitable approach than surveillance on entire classes and schools. Clinical Trial Registration: https://clinicaltrials.gov/ct2/show/NCT04448717, ClinicalTrials.gov NCT04448717.

Clustering and longitudinal change in SARS-CoV-2 seroprevalence in school children in the canton of Zurich, Switzerland: prospective cohort study of 55 schools.

OBJECTIVES: To examine longitudinal changes in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) seroprevalence and to determine the clustering of children who were seropositive within school classes in the canton of Zurich, Switzerland from June to November 2020. DESIGN: Prospective cohort study. SETTING: Switzerland had one of the highest second waves of the SARS-CoV-2 pandemic in Europe in autumn 2020. Keeping schools open provided a moderate to high exposure environment to study SARS-CoV-2 infections. Children from randomly selected schools and classes, stratified by district, were invited for serological testing of SARS-CoV-2. Parents completed questionnaires on sociodemographic and health related questions. PARTICIPANTS: 275 classes in 55 schools; 2603 children participated in June-July 2020 and 2552 in October-November 2020 (age range 6-16 years). MAIN OUTCOME MEASURES: Serology of SARS-CoV-2 in June-July and October-November 2020, clustering of children who were seropositive within classes, and symptoms in children. RESULTS: In June-July, 74 of 2496 children with serological results were seropositive; in October-November, the number had increased to 173 of 2503. Overall SARS-CoV-2 seroprevalence was 2.4% (95% credible interval 1.4% to 3.6%) in the summer and 4.5% (3.2% to 6.0%) in late autumn in children who were not previously seropositive, leading to an estimated 7.8% (6.2% to 9.5%) of children who were ever seropositive. Seroprevalence varied across districts (in the autumn, 1.7-15.0%). No significant differences were found among lower, middle, and upper school levels (children aged 6-9 years, 9-13 years, and 12-16 years, respectively). Among the 2223 children who had serology tests at both testing rounds, 28/70 (40%) who were previously seropositive became seronegative, and 109/2153 (5%) who were previously seronegative became seropositive. Symptoms were reported for 22% of children who were seronegative and 29% of children who were newly seropositive since the summer. Between July and November 2020, the ratio of children diagnosed with SARS-CoV-2 infection to those who were seropositive was 1 to 8. At least one child who was newly seropositive was detected in 47 of 55 schools and in 90 of 275 classes. Among 130 classes with a high participation rate, no children who were seropositive were found in 73 (56%) classes, one or two children were seropositive in 50 (38%) classes, and at least three children were seropositive in 7 (5%) classes. Class level explained 24% and school level 8% of variance in seropositivity in the multilevel logistic regression models. CONCLUSIONS: With schools open since August 2020 and some preventive measures in place, clustering of children who were seropositive occurred in only a few classes despite an increase in overall seroprevalence during a period of moderate to high transmission of SARS-CoV-2 in the community. Uncertainty remains as to whether these findings will change with the new variants of SARS-CoV-2 and dynamic levels of community transmission. TRIAL REGISTRATION: NCT04448717.

Seroprevalence and immunity of SARS-CoV-2 infection in children and adolescents in schools in Switzerland: design for a longitudinal, school-based prospective cohort study.

OBJECTIVES: This longitudinal cohort study aims to assess the extent and patterns of seroprevalence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies in school-attending children, and their parents and school personnel. It will examine risk factors for infection, the relationship between seropositivity and symptoms, and temporal persistence of antibodies. METHODS: The study (Ciao Corona) will enroll a regionally representative, random sample of schools in the canton of Zurich, where 18% of the Swiss population live. Children aged 5-16 years, attending primary and secondary schools, and their parents and school personnel are invited. Venous blood and saliva samples are collected for serological testing in June/July 2020, in October/November 2020, and in March/April 2021. Bi-monthly questionnaires will cover SARS-CoV-2 symptoms and tests, health, preventive behavior, and lifestyle information. Hierarchical Bayesian logistic regression models will account for sensitivity and specificity of the serological tests in the analyses and complex sampling structure, i.e., clustering within classes and schools. RESULTS AND CONCLUSIONS: This unique school-based study will allow describing temporal trends of immunity, evaluate effects of preventive measures and will inform goal-oriented policy decisions during subsequent outbreaks. Trial registration ClinicalTrials.gov Identifier: NCT04448717, registered June 26, 2020. https://clinicaltrials.gov/ct2/show/NCT04448717 .