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Objective: To compare myocarditis/pericarditis risk after COVID-19 mRNA vaccination versus SARS-CoV-2 infection, and to assess if myocarditis/pericarditis risk varies by vaccine dosing interval. Methods: In this retrospective cohort study, we used linked databases in Quebec, Ontario, and British Columbia between January 26, 2020, and September 9, 2021. We included individuals aged 12 or above who received an mRNA vaccine as the second dose or were SARS-CoV-2-positive by RT-PCR. The outcome was hospitalization/emergency department visit for myocarditis/pericarditis within 21 days of exposure. We calculated age- and sex-stratified incidence ratios (IRs) of myocarditis/pericarditis following mRNA vaccination versus SARS-CoV-2 infection. We also calculated myocarditis/pericarditis incidence by vaccine type, homologous/heterologous schedule, and dosing interval. We pooled province-specific estimates using meta-analysis. Results: Following 18,860,817 mRNA vaccinations and 860,335 SARS-CoV-2 infections, we observed 686 and 160 myocarditis/pericarditis cases, respectively. Myocarditis/pericarditis incidence was lower after vaccination than infection (IR [BNT162b2/SARS-CoV-2], 0.14; 95%CI, 0.07–0.29; IR [mRNA-1273/SARS-CoV-2], 0.28; 95%CI, 0.20–0.39). Within the vaccinated cohort, myocarditis/pericarditis incidence was lower with longer dosing intervals; IR (56 or more days/15–30 days) was 0.28 (95%CI, 0.19–0.41) for BNT162b2 and 0.26 (95%CI, 0.18–0.38) for mRNA-1273. Conclusion: Myocarditis/pericarditis risk was lower after mRNA vaccination than SARS-CoV-2 infection, and with longer intervals between primary vaccine doses.

Abstract We estimated the effectiveness of booster doses of monovalent mRNA COVID-19 vaccines against Omicron-associated severe outcomes among adults in Ontario, Canada. We used a test-negative design to estimate vaccine effectiveness (VE) against hospitalization or death among SARS-CoV-2-tested adults aged ≥50 years from January 2 to October 1, 2022, stratified by age and time since vaccination. We also compared VE during BA.1/BA.2 and BA.4/BA.5 sublineage predominance. We included 11,160 cases and 62,880 tests for test-negative controls. Depending on the age group, compared to unvaccinated adults, VE was 91–98% 7–59 days after a third dose, waned to 76–87% after ≥240 days, was restored to 92–97% 7–59 days after a fourth dose, and waned to 86–89% after ≥120 days. VE was lower and declined faster during BA.4/BA.5 versus BA.1/BA.2 predominance, particularly after ≥120 days. Here we show that booster doses of monovalent mRNA COVID-19 vaccines restored strong protection against severe outcomes for at least 3 months after vaccination. Across the entire study period, protection declined slightly over time, but waned more during BA.4/BA.5 predominance.

During the rapid deployment of COVID-19 vaccines in 2021, safety concerns may have led some pregnant individuals to postpone vaccination until after giving birth. This study aimed to describe temporal patterns and factors associated with COVID-19 vaccine series initiation after recent pregnancy in Ontario, Canada. Using the provincial birth registry linked with the COVID-19 vaccine database, we identified all individuals who gave birth between January 1 and December 31, 2021, and had not yet been vaccinated by the end of pregnancy, and followed them to June 30, 2022 (follow-up ranged from 6 to 18 months). We used cumulative incidence curves to describe COVID-19 vaccine initiation after pregnancy and assessed associations with sociodemographic, pregnancy-related, and health behavioral factors using Cox proportional hazards regression to estimate adjusted hazard ratios (aHR) and 95% confidence intervals (CI). Among 137,198 individuals who gave birth in 2021, 87,376 (63.7%) remained unvaccinated at the end of pregnancy; of these, 65.0% initiated COVID-19 vaccination by June 30, 2022. Lower maternal age (

Accurate and complete immunization data are necessary to assess vaccine coverage, safety and effectiveness. Across Canada, different methods and data sources are used to assess vaccine coverage, but these have not been systematically described. Our primary objective was to examine and describe the methods used to determine immunization coverage in Canada. The secondary objective was to compare routine infant and childhood coverage estimates derived from the Canadian 2013 Childhood National Immunization Coverage Survey (cNICS) with estimates collected from provinces and territories (P/Ts). We collected information from key informants regarding their provincial, territorial or federal methods for assessing immunization coverage. We also collected P/T coverage estimates for select antigens and birth cohorts to determine absolute differences between these and estimates from cNICS. Twenty-six individuals across 16 public health organizations participated between April and August 2015. Coverage surveys are conducted regularly for toddlers in Quebec and in one health authority in British Columbia. Across P/Ts, different methodologies for measuring coverage are used (e.g., valid doses, grace periods). Most P/Ts, except Ontario, measure up-to-date (UTD) coverage and 4 P/Ts also assess on-time coverage. The degree of concordance between P/T and cNICS coverage estimates varied by jurisdiction, antigen and age group. In addition to differences in the data sources and processes used for coverage assessment, there are also differences between Canadian P/Ts in the methods used for calculating immunization coverage. Comparisons between P/T and cNICS estimates leave remaining questions about the proportion of children fully vaccinated in Canada.

Vaccination coverage remains suboptimal in Canada and sporadic outbreaks of vaccine-preventable diseases such as measles and pertussis continue to occur. This study was undertaken to identify sociodemographic determinants of total non-vaccination (having never received any vaccine), non-vaccination for measles (0 doses) and incomplete vaccination for pertussis (< 4 doses) among 2-year-old Canadian children. Data from the 2013 Childhood National Immunization Coverage Survey (CNICS) were used. Associations between sociodemographic factors and outcomes were measured by multiple logistic regressions and adjusted odds ratios (aOR) were calculated. A total of 5,477 children were included in the analyses of total non-vaccination, and 3,899 children were included in the analysis of non-vaccination for measles and incomplete vaccination for pertussis. Overall, 2.7% of children (95% CI 2.0–3.3) had received no vaccine at all. Lower parental education, i.e., the responding parent having a high school diploma, trade certificate or less (compared with university graduation) was associated with total non-vaccination (aOR 1.99, 95% CI 1.02–3.91). Non-vaccination for measles was more frequent among children of single parent families (aOR 1.63, 95% CI 1.01–2.61) and those of parents with lower education (aOR 1.86, 95% CI 1.26–2.76). The odds of incomplete vaccination for pertussis was greater among children born outside Canada (aOR 3.10, 95% CI 1.73–5.58), of parents with lower education (aOR 1.92, 95% CI 1.41–2.62), and those whose household income was between $40,000 and $59,999 (aOR 1.47; 95% CI 1.04–2.07) or lower than $40,000 (aOR 1.58, 95% CI 1.13–2.22). Significant regional variation was also found for all outcomes. In conclusion, despite universal access to free childhood vaccines in Canada, regional variation and socioeconomic inequalities in vaccine uptake were still observed. Further analyses are warranted to identify barriers contributing to these variations.

Background There is a paucity of data on the burden of the full spectrum of community-acquired pneumonia (CAP) and acute otitis media (AOM) from outpatient and inpatient settings across the age spectrum.Methods We conducted a population-based retrospective study in Ontario and British Columbia (BC), Canada, to estimate the incidence rate of CAP and AOM in children and adults over a 14-year period using health administrative databases. CAP and AOM cases were identified from outpatient physician consultation and hospitalisation data in both provinces, and from emergency department visit data in Ontario.Results During 2005–2018, Ontario had 3 607 124 CAP, 172 290 bacterial CAP, 7814 pneumococcal pneumonia, and 8 026 971 AOM cases. The incidence rate of CAP declined from 3077/100 000 in 2005 to 2604/100 000 in 2010 before increasing to 2843/100 000 in 2018; bacterial CAP incidence rate also declined from 178/100 000 in 2005 to 112/100 000 in 2010 before increasing to 149/100 000 in 2018. The incidence rate of AOM decreased from 4192/100 000 in 2005 to 3178/100 000 in 2018. BC had 970 455 CAP, 317 913 bacterial CAP, 35 287 pneumococcal pneumonia and 2 022 871 AOM cases. The incidence rate of CAP in BC decreased from 2214/100 000 in 2005 to 1964/100 000 in 2010 before increasing to 2176/100 000 in 2018; bacterial CAP incidence rate increased from 442/100 000 in 2005 to 981/100 000 in 2018. The incidence rate of AOM decreased from 3684/100 000 in 2005 to 2398/100 000 in 2018. The incidence rate of bacterial CAP increased with age in older adults (≥65 years) with the highest burden in the oldest cohort aged ≥85 years both before and after 13-valent pneumococcal conjugate vaccine (PCV13) programme in both provinces. Hospitalised pneumococcal pneumonia decreased slightly but non-hospitalised pneumococcal pneumonia increased in BC during PCV13 period. No consistent direct benefit of PCV13 on CAP was observed in the paediatric population.Conclusions There is a substantial burden of CAP and AOM in Ontario and BC. Indirect benefits from childhood PCV vaccination and polysaccharide vaccination of older adults have not substantially decreased the burden of pneumococcal pneumonia in older adults.

Objective The objective of this study was to estimate background rates of selected thromboembolic and coagulation disorders in Ontario, Canada.Design Population-based retrospective observational study using linked health administrative databases. Records of hospitalisations and emergency department visits were searched to identify cases using International Statistical Classification of Diseases and Related Health Problems, 10th Revision, Canada diagnostic codes.Participants All Ontario residents.Primary outcome measures Incidence rates of ischaemic stroke, intracerebral haemorrhage, subarachnoid haemorrhage, deep vein thrombosis, pulmonary embolism, idiopathic thrombocytopaenia, disseminated intravascular coagulation and cerebral venous thrombosis during five prepandemic years (2015–2019) and 2020.Results The average annual population was 14 million with 51% female. The mean annual rates per 100 000 population during 2015–2019 were 127.1 (95% CI 126.2 to 127.9) for ischaemic stroke, 22.0 (95% CI 21.6 to 22.3) for intracerebral haemorrhage, 9.4 (95% CI 9.2 to 9.7) for subarachnoid haemorrhage, 86.8 (95% CI 86.1 to 87.5) for deep vein thrombosis, 63.7 (95% CI 63.1 to 64.3) for pulmonary embolism, 6.1 (95% CI 5.9 to 6.3) for idiopathic thrombocytopaenia, 1.6 (95% CI 1.5 to 1.7) for disseminated intravascular coagulation, and 1.5 (95% CI 1.4 to 1.6) for cerebral venous thrombosis. Rates were lower in 2020 than during the prepandemic years for ischaemic stroke, deep vein thrombosis and idiopathic thrombocytopaenia. Rates were generally consistent over time, except for pulmonary embolism, which increased from 57.1 to 68.5 per 100 000 between 2015 and 2019. Rates were higher for females than males for subarachnoid haemorrhage, pulmonary embolism and cerebral venous thrombosis, and vice versa for ischaemic stroke and intracerebral haemorrhage. Rates increased with age for most of these conditions, but idiopathic thrombocytopaenia demonstrated a bimodal distribution with incidence peaks at 0–19 years and ≥60 years.Conclusions Our estimated background rates help contextualise observed events of these potential adverse events of special interest and to detect potential safety signals related to COVID-19 vaccines.

Older adults are at increased risk of herpes zoster (HZ) and post-herpetic neuralgia (PHN) and HZ vaccines are available to help prevent infection. The objective of our study was to provide updated data on incidence of HZ and PHN related to clinical and demographic factors in older adults to inform immunization practices. We conducted a population-based, retrospective cohort study and included all cases of HZ seen in outpatient, emergency department, and hospital settings for adults aged 65 years and over between April 1, 2002 to August 31, 2016 in Ontario, Canada. We calculated the incidence of HZ and PHN, and estimated the proportion within each subgroup that developed PHN. We also assessed incidence by neighbourhood-level income quintile before and after the availability of vaccine for private purchase. The average annual incidence of HZ in any setting was 59.0 per 10,000 older adults, with higher incidence in outpatient as opposed to hospital settings. Incidence was higher in the oldest age groups, females, and those classified as immunocompromised or frail. Relative to the pre-vaccine era, the disparities in incidence of HZ by neighbourhood-level income increased, with higher rates of HZ and PHN seen in those residing in lower income quintiles. Additional prevention efforts should be targeted toward adults who are immunocompromised, frail, and those living in lower socioeconomic quintiles. Future work should assess the impact of the zoster vaccine program with a particular focus on equity in the publicly-funded era.

BACKGROUND:Ontario, Canada introduced a publicly-funded 13-valent pneumococcal conjugate vaccine (PCV13) for infants in 2010, replacing the 10-valent (PCV10, 2009-2010) and the 7-valent (PCV7, 2005-2009) conjugate vaccine programs; a 23-valent pneumococcal polysaccharide vaccine (PPV23) has been available for older adults since 1996. We examined the epidemiology and serotype distribution of invasive pneumococcal disease (IPD) in Ontario in the context of provincial immunization programs. METHODS:We included confirmed IPD cases reported in Ontario between 2007 and 2017. We grouped serotypes according to Ontario's current immunization program (PCV13, PPV23, and non-vaccine-preventable) and calculated incidence rates (per 100,000 population) using population data. RESULTS:Between 2007 and 2017, annual incidence of IPD in Ontario ranged between 7.3 and 9.7/100,000 per year. Measures of illness severity were high throughout the period of surveillance. After PCV13 program implementation in 2010, incidence due to PCV13 serotypes decreased significantly across all age groups, with the greatest reductions in children

In August 2011, Ontario, Canada introduced a rotavirus immunization program using Rotarix™ vaccine. No assessments of rotavirus vaccine coverage have been previously conducted in Ontario.We assessed vaccine coverage (series initiation and completion) and factors associated with uptake using the Electronic Medical Record Administrative data Linked Database (EMRALD), a collection of family physician electronic medical records (EMR) linked to health administrative data. Series initiation (1 dose) and series completion (2 doses) before and after the program's introduction were calculated. To identify factors associated with series initiation and completion, adjusted odds ratios (aOR) and 95% confidence intervals (95%CI) were calculated using logistic regression.A total of 12,525 children were included. Series completion increased each year of the program (73%, 79% and 84%, respectively). Factors associated with series initiation included high continuity of care (aOR = 2.15; 95%CI, 1.61-2.87), maternal influenza vaccination (aOR = 1.55; 95%CI,1.24-1.93), maternal immmigration to Canada in the last five years (aOR = 1.47; 95% CI, 1.05-2.04), and having no siblings (aOR = 1.62; 95%CI,1.30-2.03). Relative to the first program year, infants were more likely to initiate the series in the second year (aOR = 1.71; 95% CI 1.39-2.10) and third year (aOR = 2.02; 95% CI 1.56-2.61) of the program. Infants receiving care from physicians with large practices were less likely to initiate the series (aOR 0.91; 95%CI, 0.88-0.94, per 100 patients rostered) and less likely to complete the series (aOR 0.94; 95%CI, 0.91-0.97, per 100 patients rostered). Additional associations were identified for series completion.Family physician delivery achieved moderately high coverage in the program's first three years. This assessment demonstrates the usefulness of EMR data for evaluating vaccine coverage. Important insights into factors associated with initiation or completion (i.e. high continuity of care, smaller roster sizes, rural practice location) suggest areas for research and potential program supports.

OBJECTIVE:To evaluate the direct and indirect population impact of rotavirus (RV) immunization on hospitalizations and emergency department (ED) visits for acute gastroenteritis (AGE) in Ontario before and after the publicly-funded RV immunization program. METHODS:Administrative data was used to identify ED visits and hospitalizations for all Ontarians using ICD-10 codes. We used two outcome definitions: RV-specific AGE (RV-AGE) and codes representing RV-, other viral and cause unspecified AGE ("overall AGE"). The pre-program and public program periods were August 1, 2005 to July 31, 2011; and August 1, 2011 to March 31, 2013, respectively. A negative binominal regression model that included the effect of time was used to calculate rates and rate ratios (RRs) and 95% confidence intervals (CIs) for RV-AGE and overall AGE between periods, after adjusting for age, seasonality and secular trends. Analyses were conducted for all ages combined and age stratified. RESULTS:Relative to the pre-program period, the adjusted RRs for RV-AGE and overall AGE hospitalizations in the public program period were 0.29 (95%CI: 0.22-0.39) and 0.68 (95%CI: 0.62-0.75), respectively. Significant reductions in RV-AGE hospitalizations were noted overall and for the following age bands: < 12 months, 12-23 months, 24-35 months, 3-4 years, and 5-19 years. Significant declines in overall AGE hospitalizations were observed across all age bands, including older adults > = 65 years (RR 0.80, 95%CI: 0.72-0.90). The program was associated with adjusted RRs of 0.32 (95% CI: 0.20-0.52) for RV-AGE ED visits and 0.90 (95% CI: 0.85-0.96) for overall AGE ED visits. CONCLUSIONS:This large, population-based study provides evidence of the impact of RV vaccine in preventing hospitalizations and ED visits for RV-AGE and overall AGE, including herd effects.

Given the variation in human papillomavirus (HPV) vaccine coverage across Canada, and debate regarding delivery of HPV vaccines in Catholic schools, we studied online comments on Canadian news websites to understand public perceptions of HPV and HPV vaccine.We searched English- and French-language Canadian news websites for 2012 articles that contained the terms "HPV" or "human papillomavirus." Articles about HPV vaccinations that contained at least one comment were included. Two researchers independently coded comments, analyzing them for emerging themes.We identified 3073 comments from 1198 individuals in response to 71 news articles; 630 (52.6%) individuals expressed positive sentiments about HPV vaccination (2.5 comments/individual), 404 (33.7%) were negative (3.0 comments/individual), 34 (2.8%) were mixed (1.5 comments/individual) and 130 (10.8%) were neutral (1.6 comments/individual). Vaccine-supportive commenters believed the vaccine is safe and effective. Common themes in negative comments included concerns regarding HPV vaccine safety and efficacy, distrust of pharmaceutical companies and government, and belief that school-age children are too young for HPV vaccine. Many comments focused on whether the Catholic Church has the right to inform health policy for students, and discussion often evolved into debates regarding HPV and sexual behaviour. We noted that many individuals doubted the credibility of vaccine safety information.The majority of commenters do not appear to be against HPV vaccination, but public health messaging that focuses on both the vaccine's safety profile, and its use as a means to prevent cancer rather than sexually transmitted HPV infection may facilitate its acceptance.

Objective To examine the association between maternal mRNA covid-19 vaccination during the first trimester of pregnancy and the prevalence of major congenital anomalies in offspring.Design Population based cohort study with sibling matched analysis.Setting Multiple health administrative databases, linked and analysed at ICES, an independent, non-profit research institute that collects and analyses healthcare and demographic data, Ontario, Canada, from 16 October 2021 to 1 May 2023.Population 174 296 singleton live births >20 weeks' gestation with an expected birth date between 16 October 2021 and 1 May 2023: 34 181 (20%) born to mothers who received one or two doses of an mRNA covid-19 vaccine in the first trimester and 34 951 (20%) born to mothers who did not receive a vaccine before or during pregnancy. The sibling matched analysis included 13 312 infants exposed to a covid-19 vaccine in the first trimester and 15 089 matched older siblings with the same mother, with an expected birth date after 16 October 2016 and no reported in utero exposure to a covid-19 vaccine.Main outcome measures Major congenital anomalies, overall and grouped by specific organ systems, diagnosed within 28 days of birth.Results Major congenital anomalies were present in 832 (24.3 per 1000 live births) infants exposed to an mRNA covid-19 vaccine in the first trimester compared with 927 (26.5 per 1000 live births) infants not exposed to a vaccine, resulting in an adjusted prevalence ratio of 0.89 (95% confidence interval (CI) 0.79 to 1.01). Major congenital anomalies were present in 283 (21.3 per 1000 live births) and 343 (22.7 per 1000 live births) infants exposed to an mRNA covid-19 vaccine in the first trimester and their older siblings not exposed to a vaccine, respectively (adjusted prevalence ratio 0.91, 95% CI 0.77 to 1.07). First trimester vaccination was not associated with an increase in major congenital anomalies grouped by specific organ system in the primary or sibling matched analyses. Results were similar across a range of subgroup and sensitivity analyses.Conclusions In this large population based cohort study and sibling matched analysis, mRNA covid-19 vaccination during the first trimester of pregnancy was not associated with an increase in major congenital anomalies in offspring, overall or grouped by organ system.

IntroductionThe incidence of varicella in Canada has decreased by almost 99% since vaccination was introduced. However, variation in the timing and eligibility of vaccination programs across the country has resulted in some cohorts being under-vaccinated and therefore potentially susceptible to infection.MethodsWe used nationally representative specimens from the Biobank of Statistics Canada's Canadian Health Measures Survey (CHMS) as well as residual specimens from Ontario collected between 2009-2014 to estimate population immunity across age-groups and geography, and identify any groups at increased risk of varicella infection.ResultsThe weighted proportion of specimens with antibody levels above the threshold of protection was 93.6% (95% CI: 92.4, 95.0). Protection was lowest among those aged 3-5 years (54.3%; 95% CI: 47.3, 61.4), but increased with age. Individuals born outside Canada had more than twice the odds of varicella susceptibility than those born in Canada (aOR: 2.7; 95% CI: 1.4, 5.0; p = 0.004). There were no differences by sex or geography within Canada, and there were no statistically significant differences when Ontario CHMS sera were compared to Ontario residual sera, apart from in participants aged 12-19 year age-group, for whom the CHMS estimate (91.2%; 95% CI: 86.7, 95.7) was significantly higher (p = 0.03) than that from residual specimens (85.9%, 95% CI: 81.1, 90.8).DiscussionVaricella immunity in Canada is changing. Children appear to have low population immunity, placing them at greater risk of infection and at increased risk of severe disease as they age. Our results underscore the importance of performing periodic serosurveys to monitor further population immunity changes as the proportion of vaccine-eligible birth-cohorts increases, and to continually assess the risk of outbreaks.

Objective To assess risk of adverse pregnancy, fetal, and neonatal outcomes after a third dose (first booster dose) of covid-19 vaccine during pregnancy among individuals who had completed both doses of primary covid-19 vaccine series before pregnancy.Design Population based, retrospective cohort study.Setting Ontario, Canada, from 20 December 2021 to 31 August 2022.Participants Individuals were included if they were pregnant with an expected date of delivery from 20 December 2021 (start date of third dose eligibility for everyone ≥18 years) to 31 August 2022, who had completed the two doses of primary covid-19 messenger RNA vaccine series before pregnancy, and became eligible for a third dose (≥six months since dose two) before the end of pregnancy.Main outcome measures Pregnancy outcomes included hypertensive disorders of pregnancy, placental abruption, caesarean delivery, chorioamnionitis, and postpartum hemorrhage. Fetal and neonatal outcomes included stillbirth, preterm birth, admission to neonatal intensive care unit for >24 h, newborn 5 min Apgar score