Using physician billing claims from the Ontario Health Insurance Plan to determine individual influenza vaccination status: an updated validation study

SARS-CoV-2, Tdap, and influenza vaccination during pregnancy from 2019 to 2022 in Ontario, Canada: a population-based retrospective cohort study

BACKGROUND

Hesitancy about vaccination during pregnancy posed challenges to SARS-CoV-2 vaccination efforts. We aimed to examine rates of SARS-CoV-2 vaccination among Ontario residents who gave birth in early 2022, and to compare rates of SARS-CoV-2 vaccine uptake with rates of tetanus, diphtheria, and pertussis (Tdap) and influenza vaccination during pregnancy in 2019, 2021, and 2022.

METHODS

We conducted a population-based retrospective cohort study to describe vaccination rates among pregnant and comparable nonpregnant populations in Ontario using linked administrative data. Provincially insured females who had a live, in-hospital birth from Jan. 1 to Mar. 31 in 2019, 2021, or 2022 were our primary cohort. Using log-binomial regression, we tested associations between SARS-CoV-2 (2022) and Tdap and influenza (2019, 2021, 2022) vaccination status, with birth group and covariates. We compared SARS-CoV-2 vaccination status with the status of a matched cohort of nonpregnant females and conducted subgroup analyses by age and prenatal clinician type.

RESULTS

Among birthing people, 78.7% received their first SARS-CoV-2 vaccine dose and 74.2% received a second dose. The rate was significantly higher among nonpregnant comparators (dose 1: relative risk [RR] 0.94, 95% confidence interval [CI] 0.93-0.94; dose 2: RR 0.91, 95% CI 0.90-0.91). However, the rate of SARS-CoV-2 vaccination uptake among birthing people was higher than uptake of Tdap or influenza vaccination. Tetanus, diphtheria, and pertussis vaccination increased over time from 22.2% in 2019 to 32.6% in 2022, and influenza vaccination rose to 35.3% in 2021 but returned to prepandemic levels in 2022 (27.7%). Vaccination rates were lower among pregnant people who were young, multiparous, or residents of rural or economically deprived areas for all 3 vaccines.

INTERPRETATION

Rates of SARS-CoV-2 vaccination were lower among pregnant people than among nonpregnant comparators but were higher than rates of routinely recommended Tdap and influenza vaccinations. Pandemic urgency may have overcome a great deal of hesitancy about vaccinating against SARS-CoV-2 during pregnancy in 2022, but uptake of routinely recommended vaccines in pregnancy remains a challenge.

TRIAL REGISTRATION

Clinicaltrials.gov, no. NCT05663762.

Effectiveness of Influenza Vaccination During Pregnancy Against Laboratory-Confirmed Seasonal Influenza Among Infants Under 6 Months of Age in Ontario, Canada

BACKGROUND

Randomized trials conducted in low- and middle-income settings demonstrated efficacy of influenza vaccination during pregnancy against influenza infection among infants <6 months of age. However, vaccine effectiveness (VE) estimates from settings with different population characteristics and influenza seasonality remain limited.

METHODS

We conducted a test-negative study in Ontario, Canada. All influenza virus tests among infants <6 months from 2010 to 2019 were identified and linked with health databases to ascertain information on maternal-infant dyads. VE was estimated from the odds ratio for influenza vaccination during pregnancy among cases versus controls, computed using logistic regression with adjustment for potential confounders.

RESULTS

Among 23 806 infants tested for influenza, 1783 (7.5%) were positive and 1708 (7.2%) were born to mothers vaccinated against influenza during pregnancy. VE against laboratory-confirmed infant influenza infection was 64% (95% confidence interval [CI], 50%-74%). VE was similar by trimester of vaccination (first/second, 66% [95% CI, 40%-80%]; third, 63% [95% CI, 46%-74%]), infant age at testing (0 to <2 months, 63% [95% CI, 46%-75%]; 2 to <6 months, 64% [95% CI, 36%-79%]), and gestational age at birth (≥37 weeks, 64% [95% CI, 50%-75%]; < 37 weeks, 61% [95% CI, 4%-86%]). VE against influenza hospitalization was 67% (95% CI, 50%-78%).

CONCLUSIONS

Influenza vaccination during pregnancy offers effective protection to infants <6 months, for whom vaccines are not currently available.

The safety of seasonal influenza vaccination among adults prescribed immune checkpoint inhibitors: A self-controlled case series study using administrative data

BACKGROUND

Immune checkpoint inhibitor (ICI) therapy for patients undergoing cancer treatment carries a risk of severe immune-related adverse events (IRAEs). Questions remain about whether seasonal influenza vaccination might increase the risk of developing IRAEs among these patients given that vaccines are immunomodulatory. Previous vaccine safety studies on patients with cancer prescribed ICI therapy have demonstrated conflicting results.

METHODS

Using health administrative data from Ontario, Canada among adults diagnosed with cancer who had been prescribed ICI therapy and who had received an influenza vaccine from 2012 to 2019, we conducted a self-controlled case series study. The pre-vaccination control period started 42-days post-ICI initiation until 14-days prior to vaccination, the risk period was 1-42 days post-vaccination, and the post-vaccination control period was after the risk period until ICI discontinuation or a maximum period of two years. Emergency department (ED) visit(s) and/or hospitalization for any cause after ICI initiation was used to identify severe IRAEs. We fitted a fixed-effects Poisson regression model accounting for seasonality and calendar time to estimate relative incidence of IRAEs between risk and control periods.

RESULTS

We identified 1133 records of cancer patients who received influenza vaccination while prescribed ICI therapy. Most were aged ≥ 66 years (73 %), were male (63 %), had lung cancer (54 %), and had received ICI therapy with a programmed cell death protein 1(PD-1) inhibitor (91 %). A quarter (26 %) experienced an ED visit and/or hospitalization during the observation period. Rates of ED visits and/or hospitalizations in the risk vs. control periods were similar, with an incidence rate ratio of 1.04 (95 % CI: 0.75-1.45). Subgroup and sensitivity analyses yielded similar results.

CONCLUSION

Seasonal influenza vaccination was not associated with an increased incidence of ED visit or hospitalization among adults with cancer treated with ICI therapy and our results support further evidence of vaccine safety.

Measuring waning protection from seasonal influenza vaccination during nine influenza seasons, Ontario, Canada, 2010/11 to 2018/19

BackgroundWaning immunity from seasonal influenza vaccination can cause suboptimal protection during peak influenza activity. However, vaccine effectiveness studies assessing waning immunity using vaccinated and unvaccinated individuals are subject to biases.AimWe examined the association between time since vaccination and laboratory-confirmed influenza to assess the change in influenza vaccine protection over time.MethodsUsing linked laboratory and health administrative databases in Ontario, Canada, we identified community-dwelling individuals aged ≥ 6 months who received an influenza vaccine before being tested for influenza by RT-PCR during the 2010/11 to 2018/19 influenza seasons. We estimated the adjusted odds ratio (aOR) for laboratory-confirmed influenza by time since vaccination (categorised into intervals) and for every 28 days.ResultsThere were 53,065 individuals who were vaccinated before testing for influenza, with 10,264 (19%) influenza-positive cases. The odds of influenza increased from 1.05 (95% CI: 0.91-1.22) at 42-69 days after vaccination and peaked at 1.27 (95% CI: 1.04-1.55) at 126-153 days when compared with the reference interval (14-41 days). This corresponded to 1.09-times increased odds of influenza every 28 days (aOR = 1.09; 95% CI: 1.04-1.15). Individuals aged 18-64 years showed the greatest decline in protection against influenza A(H1N1) (aORper 28 days = 1.26; 95% CI: 0.97-1.64), whereas for individuals aged ≥ 65 years, it was against influenza A(H3N2) (aORper 28 days = 1.20; 95% CI: 1.08-1.33). We did not observe evidence of waning vaccine protection for individuals aged < 18 years.ConclusionsInfluenza vaccine protection wanes during an influenza season. Understanding the optimal timing of vaccination could ensure robust protection during seasonal influenza activity.

Impact of antiviral therapy on short- and long-term outcomes of patients with chronic obstructive pulmonary disease after influenza infection

Background

Respiratory complications often accompany influenza in patients with chronic obstructive pulmonary disease (COPD). In this retrospective study, we quantified the impact of antiviral therapy on exacerbations, healthcare resource utilization (HRU), and costs in patients with COPD across 5 influenza seasons.

Methods

Using claims data from US MarketScan® databases, we identified patients with COPD who had an influenza diagnosis during the 2012-2016 influenza seasons. Patients who received a neuraminidase inhibitor within 48 h of diagnosis (N = 4134) were identified and propensity score-matched 1:1 to a comparator cohort of untreated patients. We determined COPD- and pneumonia-related HRU and costs during month 1, each subsequent quarter, and months 2-13.

Results

Antiviral-treated patients had a significantly lower frequency of COPD-related outcomes than untreated patients during all periods (exacerbations: 10.4% vs 18.2% [month 1] and 17.7% vs 24.2% [months 2-13]; inpatient visit: 2.5% vs 7.9% [month 1] and 3.8% vs 6.7% [months 2-13]; P < 0.0001, all comparisons). Treated patients also had significantly lower outpatient and emergency department (ED) visits beyond month 1. Pneumonia-related inpatient, ED, and outpatient visits were significantly lower in antiviral-treated patients than in untreated patients over all periods (P < 0.0001, all comparisons). In all HRU categories, COPD- and pneumonia-related costs were significantly lower in treated patients over all periods (month-1 ED visit costs were higher).

Conclusions

Antiviral treatment in patients with COPD and influenza is associated with significantly lower HRU and costs in the postinfection month and for an entire year following infection compared with untreated patients.

Trends and characteristics of Tdap vaccination during pregnancy in Ontario, Canada: a retrospective cohort study

BACKGROUND

In February 2018, Canada's National Advisory Committee on Immunization (NACI) recommended tetanus toxoid, reduced diphtheria toxoid and acellular pertussis (Tdap) vaccination during pregnancy to protect newborns against pertussis infection. We sought to describe pre- and postrecommendation trends in Tdap vaccination coverage among pregnant Ontario residents.

METHODS

Using linked health administrative databases, we conducted a population-based retrospective cohort study of all pregnant individuals who gave birth in Ontario hospitals between April 2012 and March 2020. We described Tdap vaccination patterns in pregnancy for the entire study period and before and after the NACI recommendation. We used log-binomial regression to identify characteristics associated with Tdap vaccination during pregnancy.

RESULTS

Among the 991 850 deliveries included, 7.0% of pregnant individuals received the Tdap vaccination during pregnancy. Vaccine coverage increased from 0.4% in 2011/12 to 29.2% in 2019/20. Coverage was highest among individuals who were older, had no previous live births, had adequate prenatal care and received maternity care primarily from a family physician. After adjustment, characteristics associated with lower coverage included younger maternal age, having a multiple birth, residing in a rural location and higher area material deprivation. In 2019/20, 71.0% of vaccinated individuals received the Tdap vaccination during the recommended gestational window (27-32 wk). Stratified analyses of the pre- and postrecommendation cohorts yielded similar findings to the main analyses with a few gradient differences after adjustment.

INTERPRETATION

During pregnancy, Tdap vaccination coverage increased substantially in Ontario between 2011/12 and 2019/20, most notably after recommendations for universal Tdap vaccination during pregnancy began in Canada. To further improve vaccine coverage in the obstetric setting, public health strategies should consider tailoring their programs to reach subpopulations with lower vaccine coverage.

Association of Influenza Vaccination With SARS-CoV-2 Infection and Associated Hospitalization and Mortality Among Patients Aged 66 Years or Older

Importance

Vaccine effectiveness studies have rarely implemented strategies to reduce the healthy vaccinee bias arising from differences in health care-seeking behavior between vaccinated and unvaccinated individuals. Although previous observational studies suggest that influenza vaccination is associated with a reduced risk of SARS-CoV-2-associated outcomes, the healthy vaccinee bias may have led to overestimating the vaccination effect.

Objective

To estimate the association between influenza vaccination and SARS-CoV-2-associated outcomes.

Design, Setting, and Participants

This cohort study was conducted over 2 consecutive influenza vaccination campaigns (2019-2020 and 2020-2021), owing to the substantial COVID-19 burden and the greater validity of influenza vaccination data in the studied age group. The study population included community-dwelling adults aged 66 years or older in Ontario, Canada.

Exposure

Influenza vaccination for a given season.

Main Outcomes and Measures

The outcomes of interest included SARS-CoV-2 infection, SARS-CoV-2-associated hospitalization, SARS-CoV-2-associated death, and a composite of SARS-CoV-2-associated hospitalization or death. Cox proportional hazards models were used to measure the association between influenza vaccination and SARS-CoV-2-associated outcomes, censoring individuals who moved into long-term care, received COVID-19 vaccines, or died before the observation period end date. Primary care periodic health examinations (PHEs) were explored as a negative tracer exposure (ie, no association expected with SARS-CoV-2 outcomes) and as an effect modifier of the association between influenza vaccination and SARS-CoV-2 outcomes.

Results

Of 2 922 449 individuals aged 66 years or older (54.2% female) living in Ontario, 2 279 805 were included in the study. Among these, 1 234 647 (54.2%) were female and 1 045 158 (45.8%) were male; their mean (SD) age was 75.08 (7.21) years. Those who had received influenza vaccination exhibited a lower incidence of SARS-CoV-2 infection than unvaccinated individuals for the 2019-2020 cohort (adjusted hazards ratio [aHR], 0.78; 95% CI, 0.73-0.84) and the 2020-2021 cohort (aHR, 0.76; 95% CI, 0.74-0.78). This association was also observed for SARS-CoV-2-associated hospitalization or death (2019-2020: aHR, 0.83; 95% CI, 0.74-0.92; 2020-2021: aHR, 0.66; 95% CI, 0.63-0.70). Similarly, undergoing a PHE was also associated with a lower incidence of SARS-CoV-2 infection (aHR, 0.85; 95% CI, 0.78-0.91) and SARS-CoV-2-associated hospitalization or death (aHR, 0.80; 95% CI, 0.70-0.90), and modified the association between influenza vaccination and SARS-CoV-2 infection for vaccinated individuals who underwent PHE (aHR, 0.62; 95% CI, 0.52-0.74) and for vaccinated individuals who did not undergo PHE (aHR, 0.81; 95% CI, 0.76-0.87), and also SARS-CoV-2-associated hospitalization or death in vaccinated individuals who underwent PHE (aHR, 0.66; 95% CI, 0.49-0.88) and vaccinated individuals who did not undergo PHE (aHR, 0.85, 95% CI, 0.76-0.95).

Conclusions and Relevance

The findings of this cohort study suggest that undergoing a PHE may at least partially modify the association between influenza vaccination and SARS-CoV-2-associated outcomes in individuals aged 66 years or older, providing evidence of the healthy vaccinee bias that may affect vaccine effectiveness studies.

Morbidity and health care use among siblings of children with cancer: A population-based study

BACKGROUND

Childhood cancer impacts the entire family unit. We sought to investigate its impact on the long-term physical health outcomes of siblings of children with cancer.

PROCEDURE

Pediatric cancer patients diagnosed in Ontario, Canada between 1988 and 2016 were linked to biological siblings. Sibling cases were matched to population controls based on sex, age, geographic location, and number of other children in the family. After individual linkage to health services data, we compared several outcomes between sibling cases and controls: (a) physical health conditions (such as diabetes, hypertension, and death); (b) acute health care use (hospitalization, low- and high-acuity emergency department [ED] visits); and (c) preventive health care use (periodic health checkups, influenza vaccinations). Cox proportional hazards, recurrent event, or logistic regression models were used as appropriate.

RESULTS

We identified 8529 sibling cases and 30,364 matched controls (median age at index: 6 years, median age at last follow-up 17 years). Compared to controls, siblings were at increased risk of hypertension (hazard ratio [HR] 1.8; 95% confidence interval [CI] 1.1-2.9; p = .01), had higher rates of low- and high-acuity ED visits (rate ratio 1.1; 95% CI 1.1-1.2; p < .001), and increased risk of hospitalization (HR 1.1; 95% CI 1.1-1.2; p < .001). Sibling cases were also more likely to receive preventive health care (p < .05).

CONCLUSION

Increased risk of hypertension, high-acuity ED visits, and hospitalizations suggest that siblings may experience poorer health compared to controls. Counseling families about this potential increased risk and long-term follow-up of siblings to monitor their physical health may be justified.

Impact of influenza infection on the short- and long-term health of patients with chronic obstructive pulmonary disease

BACKGROUND

Influenza is a common cause of acute respiratory infection that leads to exacerbation of underlying chronic obstructive pulmonary disease (COPD). To elucidate the short- and long-term effects of influenza in patients with COPD, we examined health care resource utilization (HRU) and costs up to 13 months following influenza infection.

METHODS

We conducted a retrospective cohort study using U.S. insurance claims data from MarketScan. Patients with an influenza diagnosis during the 2012-2014 influenza seasons and continuous enrollment in a health plan from 12 months before to 13 months after the index influenza diagnosis were identified and propensity score-matched 1:5 to controls without evidence of influenza. COPD- and pneumonia-related outcomes were assessed over 13 months following influenza diagnosis.

RESULTS

COPD-associated outcomes after diagnosis were significantly worse in patients with influenza (n = 7,087) vs. controls (n = 35,435) during the first month (exacerbation: 16.1 vs. 3.4%; outpatient visits: 57.1 vs. 35.2%; emergency department (ED) visits: 10.5 vs. 1.8%; and inpatient visits: 5.6 vs. 0.7%) and months 2-13 (exacerbation: 25.1 vs. 21.1%; outpatient visits: 86.1 vs. 85.8%; ED visits: 20.0 vs. 15.7%; and inpatient visits: 6.5 vs. 5.3%). COPD- and pneumonia-associated costs for months 1 and 2-13 were higher in patients with influenza.

LIMITATIONS

The study was subject to a residual imbalance between cohorts despite propensity score matching. The use of diagnostic codes to select patients and identify complications could introduce inaccuracies in estimating events.

CONCLUSIONS

HRU and costs were higher in COPD patients with influenza during the first month and over the entire year following infection. This suggests influenza has an impact on respiratory health in patients with COPD that lasts beyond the acute infection.

Digital intervention increases influenza vaccination rates for people with diabetes in a decentralized randomized trial

People with diabetes (PWD) have an increased risk of developing influenza-related complications, including pneumonia, abnormal glycemic events, and hospitalization. Annual influenza vaccination is recommended for PWD, but vaccination rates are suboptimal. The study aimed to increase influenza vaccination rate in people with self-reported diabetes. This study was a prospective, 1:1 randomized controlled trial of a 6-month Digital Diabetes Intervention in U.S. adults with diabetes. The intervention group received monthly messages through an online health platform. The control group received no intervention. Difference in self-reported vaccination rates was tested using multivariable logistic regression controlling for demographics and comorbidities. The study was registered at clinicaltrials.gov: NCT03870997. A total of 10,429 participants reported influenza vaccination status (5158 intervention, mean age (±SD) = 46.8 (11.1), 78.5% female; 5271 control, Mean age (±SD) = 46.7 (11.2), 79.4% female). After a 6-month intervention, 64.2% of the intervention arm reported influenza vaccination, vers us 61.1% in the control arm (diff = 3.1, RR = 1.05, 95% CI [1.02, 1.08], p = 0.0013, number needed to treat = 33 to obtain 1 additional vaccination). Completion of one or more intervention messages was associated with up to an 8% increase in vaccination rate (OR 1.27, 95% CI [1.17, 1.38], p < 0.0001). The intervention improved influenza vaccination rates in PWD, suggesting that leveraging new technology to deliver knowledge and information can improve influenza vaccination rates in high-risk populations to reduce public health burden of influenza. Rapid cycle innovation could maximize the effects of these digital interventions in the future with other populations and vaccines.

Influenza Vaccine Effectiveness Against All-Cause Mortality Following Laboratory-Confirmed Influenza in Older Adults, 2010-2011 to 2015-2016 Seasons in Ontario, Canada

BACKGROUND

Older adults are at increased risk of mortality from influenza infections. We estimated influenza vaccine effectiveness (VE) against mortality following laboratory-confirmed influenza.

METHODS

Using a test-negative design study and linked laboratory and health administrative databases in Ontario, Canada, we estimated VE against all-cause mortality following laboratory-confirmed influenza for community-dwelling adults aged >65 years during the 2010-2011 to 2015-2016 influenza seasons.

RESULTS

Among 54 116 older adults tested for influenza across the 6 seasons, 6837 died within 30 days of specimen collection. Thirteen percent (925 individuals) tested positive for influenza, and 50.6% were considered vaccinated for that season. Only 23.2% of influenza test-positive cases had influenza recorded as their underlying cause of death. Before and after multivariable adjustment, we estimated VE against all-cause mortality following laboratory-confirmed influenza to be 20% (95% confidence interval [CI], 8%-30%) and 20% (95% CI, 7%-30%), respectively. This estimate increased to 34% after correcting for influenza vaccination exposure misclassification. We observed significant VE against deaths following influenza confirmation during 2014-2015 (VE = 26% [95% CI, 5%-42%]). We also observed significant VE against deaths following confirmation of influenza A/H1N1 and A/H3N2, and against deaths with COPD as the underlying cause.

CONCLUSIONS

These results support the importance of influenza vaccination in older adults, who account for most influenza-associated deaths annually.

Health Outcomes in Young Children Following Pertussis Vaccination During Pregnancy

BACKGROUND AND OBJECTIVES

Maternal immunization with tetanus, diphtheria, and acellular pertussis vaccine (Tdap) is routinely recommended in many countries as a strategy to protect young infants against severe pertussis infection; few studies have assessed whether prenatal exposure to the vaccine is associated with any longer-term adverse health effects in children. We evaluated the long-term safety of exposure to Tdap vaccination during pregnancy.

METHODS

Population-based retrospective cohort study conducted in Ontario, Canada using multiple linked province-wide health administrative databases. All live births between April 2012 and March 2017 were included, and children were followed for up to 6 years to ascertain study outcomes. Children exposed to prenatal Tdap were propensity score matched to unexposed children at a 1:5 ratio. Tdap vaccination during pregnancy was ascertained by using vaccine-specific fee codes. Immune-related (infectious diseases, asthma) and nonimmune-related (neoplasm, sensory disorders) outcomes and a nonspecific morbidity outcome (urgent or inpatient health service use) were evaluated from birth to end of follow-up.

RESULTS

Of 625 643 live births, 12 045 (1.9%) were exposed to Tdap in utero. There were no significant increased risks of adverse childhood outcomes and prenatal Tdap exposure; however, we observed inverse associations (adjusted incidence rate ratio [95% confidence interval]) with upper respiratory infections (0.94 [0.90-0.99]), gastrointestinal infections (0.85 [0.79-0.91]), and urgent and inpatient health service use (0.93 [0.91-0.96]).

CONCLUSIONS

Exposure to Tdap vaccination in pregnancy was not associated with any increased risk of adverse health outcomes in early childhood, supporting the long-term safety of Tdap administration in pregnancy.

Healthcare Resource Use and Burden Associated with Influenza Transmission Among Household Members with a Primary Infection: Commercial Claims Data Analysis

PURPOSE

To assess the burden of influenza transmission and care-seeking patterns over 3 influenza seasons among commercially insured households with a primary influenza infection.

PATIENTS AND METHODS

This retrospective cohort study used commercial claims data from the US MarketScan® Commercial and Medicare Supplemental databases for the 2014, 2015, and 2016 influenza seasons. Patients with a billed diagnosis of influenza and with coverage for at least 1 household member under the same health plan policy were included. A secondary diagnosed case was defined as a diagnosis of influenza in a second household member occurring within 14 days of the index case in a household.

RESULTS

Among 1,224,808 households with ≥2 members and a primary case of influenza, a secondary case of influenza was reported in 119,883 households (9.8%). A secondary diagnosed case of influenza occurred within 4 days of the primary diagnosis in 93,883 (78.3%) of those households. Both primary and secondary diagnosed influenza cases occurred most often among children (~60%). Household size was positively correlated to both the risk of a second case (6.4% of households with 2 or 3 members versus 12.6% of households with ≥4 members, P < 0.001) and the time to diagnosis of a second case (Spearman rank correlation coefficient = 0.09; P < 0.001).

CONCLUSION

Claims data for 3 influenza seasons (2014, 2015, 2016) showed that intrahousehold transmission of influenza occurs in approximately 10% of households with a primary case and poses a higher burden on larger households. Intrahousehold transmission of influenza represents a large healthcare resource use burden, with an unmet need for interventions that limit transmission.

A systematic review of quantitative bias analysis applied to epidemiological research

BACKGROUND

Quantitative bias analysis (QBA) measures study errors in terms of direction, magnitude and uncertainty. This systematic review aimed to describe how QBA has been applied in epidemiological research in 2006-19.

METHODS

We searched PubMed for English peer-reviewed studies applying QBA to real-data applications. We also included studies citing selected sources or which were identified in a previous QBA review in pharmacoepidemiology. For each study, we extracted the rationale, methodology, bias-adjusted results and interpretation and assessed factors associated with reproducibility.

RESULTS

Of the 238 studies, the majority were embedded within papers whose main inferences were drawn from conventional approaches as secondary (sensitivity) analyses to quantity-specific biases (52%) or to assess the extent of bias required to shift the point estimate to the null (25%); 10% were standalone papers. The most common approach was probabilistic (57%). Misclassification was modelled in 57%, uncontrolled confounder(s) in 40% and selection bias in 17%. Most did not consider multiple biases or correlations between errors. When specified, bias parameters came from the literature (48%) more often than internal validation studies (29%). The majority (60%) of analyses resulted in >10% change from the conventional point estimate; however, most investigators (63%) did not alter their original interpretation. Degree of reproducibility related to inclusion of code, formulas, sensitivity analyses and supplementary materials, as well as the QBA rationale.

CONCLUSIONS

QBA applications were rare though increased over time. Future investigators should reference good practices and include details to promote transparency and to serve as a reference for other researchers.

Obstetric and perinatal health outcomes after pertussis vaccination during pregnancy in Ontario, Canada: a retrospective cohort study

BACKGROUND

In February 2018, Canada's National Advisory Committee on Immunization recommended maternal vaccination with tetanus-diphtheria-acellular pertussis (Tdap) vaccine during pregnancy to prevent severe pertussis infection in young infants. This study assessed the relation between maternal Tdap vaccination and obstetric and perinatal outcomes in Ontario.

METHODS

We performed a population-based cohort study of all births from April 2012 to March 2017 using multiple linked health administrative databases. We used Cox regression with a time-dependent exposure variable to estimate adjusted hazard ratios (HRs) for preterm birth (< 37 wk), very preterm birth (< 32 wk) and stillbirth. We assessed remaining outcomes (gestational hypertension, chorioamnionitis, postpartum hemorrhage, severe postpartum hemorrhage, being small for gestational age, neonatal intensive care unit stay > 24 h, composite neonatal morbidity) using log-binomial regression to generate adjusted risk ratios (RRs). We adjusted estimates for potential confounding using propensity score weighting.

RESULTS

Of 615 213 infants (live births and stillbirths), 11 519 were exposed to Tdap vaccination in utero. There was no increased risk for preterm birth (adjusted HR 0.98, 95% confidence interval [CI] 0.91-1.06), very preterm birth (adjusted HR 1.10, 95% CI 0.86-1.41), stillbirth (adjusted HR 1.15, 95% CI 0.82-1.60) or being small for gestational age (adjusted RR 0.96, 95% CI 0.90-1.02). The risks of a neonatal intensive care unit stay exceeding 24 hours (adjusted RR 0.82, 95% CI 0.76-0.88) and neonatal morbidity (adjusted RR 0.81, 95% CI 0.75-0.87) were decreased. There was no association with chorioamnionitis (adjusted RR 1.17, 95% CI 0.99-1.39), postpartum hemorrhage (adjusted RR 1.01, 95% CI 0.91-1.13) or severe postpartum hemorrhage (adjusted RR 0.79, 95% CI 0.55-1.13), but we observed a reduced risk of gestational hypertension (adjusted RR 0.87, 95% CI 0.78-0.96).

INTERPRETATION

Our results complement evidence that maternal Tdap vaccination is not associated with adverse outcomes in mothers or infants. Ongoing evaluation in Canada is needed as maternal Tdap vaccination coverage increases in coming years.

Primary care physician volume and quality of care for older adults with dementia: a retrospective cohort study

BACKGROUND

Some jurisdictions restrict primary care physicians' daily patient volume to safeguard quality of care for complex patients. Our objective was to determine whether people with dementia receive lower-quality care if their primary care physician sees many patients daily.

METHODS

Population-based retrospective cohort study using health administrative data from 100,256 community-living adults with dementia aged 66 years or older, and the 8,368 primary care physicians who cared for them in Ontario, Canada. Multivariable Poisson GEE regression models tested whether physicians' daily patient volume was associated with the adjusted likelihood of people with dementia receiving vaccinations, prescriptions for cholinesterase inhibitors, benzodiazepines, and antipsychotics from their primary care physician.

RESULTS

People with dementia whose primary care physicians saw ≥ 30 patients daily were 32% (95% CI: 23% to 41%, p < 0.0001) and 25% (95% CI: 17% to 33%, p < 0.0001) more likely to be prescribed benzodiazepines and antipsychotic medications, respectively, than patients of primary care physicians who saw < 20 patients daily. Patients were 3% (95% CI: 0.4% to 6%, p = 0.02) less likely to receive influenza vaccination and 8% (95% CI: 4% to 13%, p = 0.0001) more likely to be prescribed cholinesterase inhibitors if their primary care physician saw ≥ 30 versus < 20 patients daily.

CONCLUSIONS

People with dementia were more likely to receive both potentially harmful and potentially beneficial medications, and slightly less likely to be vaccinated by high-volume primary care physicians.

The impact of repeated vaccination using 10-year vaccination history on protection against influenza in older adults: a test-negative design study across the 2010/11 to 2015/16 influenza seasons in Ontario, Canada

Introduction

Annual influenza vaccination is recommended for older adults, but evidence regarding the impact of repeated vaccination has been inconclusive.

Aim

We investigated vaccine effectiveness (VE) against laboratory-confirmed influenza and the impact of repeated vaccination over 10 previous seasons on current season VE among older adults.

Methods

We conducted an observational test-negative study in community-dwelling adults aged > 65 years in Ontario, Canada for the 2010/11 to 2015/16 seasons by linking laboratory and health administrative data. We estimated VE using multivariable logistic regression. We assessed the impact of repeated vaccination by stratifying by previous vaccination history.

Results

We included 58,304 testing episodes for respiratory viruses, with 11,496 (20%) testing positive for influenza and 31,004 (53%) vaccinated. Adjusted VE against laboratory-confirmed influenza for the six seasons combined was 21% (95% confidence interval (CI): 18 to 24%). Patients who were vaccinated in the current season, but had received no vaccinations in the previous 10 seasons, had higher current season VE (34%; 95%CI: 9 to 52%) than patients who had received 1–3 (26%; 95%CI: 13 to 37%), 4–6 (24%; 95%CI: 15 to 33%), 7–8 (13%; 95%CI: 2 to 22%), or 9–10 (7%; 95%CI: −4 to 16%) vaccinations (trend test p = 0.001). All estimates were higher after correcting for misclassification of current season vaccination status. For patients who were not vaccinated in the current season, residual protection rose significantly with increasing numbers of vaccinations received previously.

Conclusions

Although VE appeared to decrease with increasing numbers of previous vaccinations, current season vaccination likely provides some protection against influenza regardless of the number of vaccinations received over the previous 10 influenza seasons.

Influenza Vaccine Effectiveness in Preventing Hospitalizations in Older Patients With Chronic Obstructive Pulmonary Disease

BACKGROUND

Annual influenza immunization is recommended for people with chronic obstructive pulmonary disease (COPD) by all major COPD clinical practice guidelines. We sought to determine the seasonal influenza vaccine effectiveness (VE) against laboratory-confirmed influenza-associated hospitalizations among older adults with COPD.

METHODS

We conducted a test-negative study of influenza VE in community-dwelling older adults with COPD in Ontario, Canada using health administrative data and respiratory specimens collected from patients tested for influenza during the 2010-11 to 2015-16 influenza seasons. Influenza vaccination was ascertained from physician and pharmacist billing claims. Multivariable logistic regression was used to estimate the adjusted odds ratio of influenza vaccination in people with, compared to those without, laboratory-confirmed influenza.

RESULTS

Receipt of seasonal influenza vaccine was associated with an adjusted 22% (95% confidence interval [CI], 15%-27%) reduction in laboratory-confirmed influenza-associated hospitalization. Adjustment for potential misclassification of vaccination status increased this to 43% (95% CI, 35%-52%). Vaccine effectiveness was not found to vary by patient- or influenza-related variables.

CONCLUSIONS

During the studied influenza seasons, influenza vaccination was at least modestly effective in reducing laboratory-confirmed influenza-associated hospitalizations in people with COPD. The imperfect effectiveness emphasizes the need for better influenza vaccines and other preventive strategies.

Using population-wide administrative and laboratory data to estimate type- and subtype-specific influenza vaccine effectiveness: a surveillance protocol

INTRODUCTION

The appropriateness of using routinely collected laboratory data combined with administrative data for estimating influenza vaccine effectiveness (VE) is still being explored. This paper outlines a protocol to estimate influenza VE using linked laboratory and administrative data which could act as a companion to estimates derived from other methods.

METHODS AND ANALYSIS

We will use the test-negative design to estimate VE for each influenza type/subtype and season. Province-wide individual-level records of positive and negative influenza tests at the Provincial Laboratory for Public Health in Alberta will be linked, by unique personal health numbers, to administrative databases and vaccination records held at the Ministry of Health in Alberta to determine covariates and influenza vaccination status, respectively. Covariates of interests include age, sex, immunocompromising chronic conditions and healthcare setting. Cases will be defined based on an individual's first positive influenza test during the season, and potential controls will be defined based on an individual's first negative influenza test during the season. One control for each case will be randomly selected based on the week the specimen was collected. We will estimate VE using multivariable logistic regression.

ETHICS AND DISSEMINATION

Ethics approval was obtained from the University of Alberta's Health Research Ethics Board-Health Panel under study ID Pro00075997. Results will be disseminated by public health officials in Alberta.

Influenza Vaccine Effectiveness Among Patients With Cancer: A Population-Based Study Using Health Administrative and Laboratory Testing Data From Ontario, Canada

PURPOSE

Seasonal influenza vaccination is recommended for patients with cancer despite concerns of disease or treatment-associated immunosuppression. The objective of this study was to evaluate vaccine effectiveness (VE) against laboratory-confirmed influenza for patients with cancer.

PATIENTS AND METHODS

We conducted an observational test-negative design study of previously diagnosed patients with cancer 18 years of age and older who underwent influenza testing during the 2010-2011 to 2015-2016 influenza seasons in Ontario, Canada. We linked individual-level cancer registry, respiratory virus testing, and health administrative data to identify the study population and outcomes. Vaccination status was determined from physician and pharmacist billing claims. We used multivariable logistic regression to estimate VE, adjusting for age, sex, rurality, income quintile, cancer characteristics, chemotherapy exposure, comorbidities, previous health care use, influenza season, and calendar time.

RESULTS

We identified 26,463 patients with cancer who underwent influenza testing, with 4,320 test-positive cases (16%) and 11,783 (45%) vaccinated. Mean age was 70 years, 52% were male, mean time since diagnosis was 6 years, 69% had solid tumor malignancies, and 23% received active chemotherapy. VE against laboratory-confirmed influenza was 21% (95% CI, 15% to 26%), and VE against laboratory-confirmed influenza hospitalization was 20% (95% CI, 13% to 26%). For patients with solid tumor malignancies, VE was 25% (95% CI, 18% to 31%), compared with 8% (95% CI, -5% to 19%) for patients with hematologic malignancies (P = .015). Active chemotherapy usage did not significantly affect VE, especially among patients with solid tumor cancer.

CONCLUSION

Our results support recommendations for influenza vaccination for patients with cancer. VE was decreased for patients with hematologic malignancies, and there was no significant difference in VE among patients with solid tumor cancer receiving active chemotherapy. Strategies to optimize influenza prevention among patients with cancer are warranted.

Estimating age-specific influenza-associated asthma morbidity in Ontario, Canada

BACKGROUND

There is a need to quantify the potential benefits of influenza-focused interventions in reducing asthma morbidity at a population level. This study aims to estimate age-specific annual excess asthma morbidity attributable to influenza in Ontario, Canada.

METHODS

Weekly counts of hospitalizations, emergency department (ED) visits and outpatient physician office visits for asthma were obtained from health administrative data in Ontario from 2010 to 2015, for ages 0-14, 15-59 and 60+. Asthma morbidity was modelled as a function of influenza A and B activity using linear regression, controlling for seasonal and long-term trend, mean temperature and respiratory syncytial virus. Excess asthma morbidity attributable to influenza was calculated as the difference between full model predictions and model predictions with influenza A and B variables set to 0.

RESULTS

Annually, influenza was associated with the following rates of excess asthma morbidity, per 100,000 people with prevalent asthma: 12.5 hospitalizations for ages 15-59 (95% confidence interval (CI): 1.1-23.5); 35.7 hospitalizations for ages 60+ (95% CI: 3.3-67.1); 114.1 ED visits for ages 15-59 (95% CI: 46.9-181.6); 154.6 ED visits for ages 60+ (95% CI: 86.7-223.3); and 1025.7 outpatient physician office visits for ages 60+ (95% CI: 79.0-1877.3).

CONCLUSIONS

Influenza was associated with excess asthma hospitalizations and ED visits for ages 15-59 and 60+ and outpatient physician office visits for ages 60+. Individuals with asthma aged 15-59 and 60+ might be important targets for influenza-focused interventions, to reduce asthma morbidity at the population level.

Characteristics of patients vaccinated against influenza in physician offices versus pharmacies and predictors of vaccination location: a cross-sectional study

BACKGROUND

Little is known about those vaccinated against influenza after pharmacists were added to the Ontario Universal Influenza Immunization Program, in 2012. Our aim was to identify characteristics of patients vaccinated against influenza and predictors of vaccination at a physician's office versus a community pharmacy.

METHODS

We conducted a cross-sectional study of Ontario residents who had a record of receipt of an influenza vaccine between October and March in the 2013/14 and 2015/16 influenza seasons in Ontario using health administrative databases. We used Poisson regression models to estimate associations between baseline characteristics and the receipt of influenza vaccination in a community pharmacy. All analyses were stratified by age group (≤ 65 yr or ≥ 66 yr).

RESULTS

Overall, we found a 7.9% decrease in vaccinations administered in 2015/16 (2 454 178) compared to 2013/14 (2 677 278). The number of patients vaccinated in community pharmacies increased between the 2 periods (757 729 [28.3%] in 2013/14 v. 859 794 [35.0%] in 2015/16). Living in nonurban areas or higher-income neighbourhoods, not identifying as an immigrant, not having a diagnosis of diabetes or hypertension, and receiving a pharmacist service on the same day as the vaccination were predictors of being vaccinated in a pharmacy, regardless of age group. Among patients aged 66 or more, those who had a hospital admission in the previous year were more likely to be vaccinated in a pharmacy than in a physician's office (adjusted incidence rate ratio [IRR] 1.08, 95% confidence interval [CI] 1.06-1.09), whereas those with higher annual medication costs were more likely to be vaccinated in a physician's office. The location of the previous season's vaccination predicted the current season's place of vaccination (age ≥ 66 yr: physician's office: adjusted IRR 0.56 [95% CI 0.56-0.57], pharmacy: adjusted IRR 2.37 [95% CI 2.35-2.39]; age ≤ 65 yr: physician's office: adjusted IRR 0.57 [95% CI 0.57-0.57], pharmacy: adjusted IRR 2.19 [95% CI 2.18-2.20]).

INTERPRETATION

For the 2013/14 and 2015/16 influenza seasons, the influenza vaccine was administered more frequently in physician offices than in community pharmacies, but the proportion of patients vaccinated in community pharmacies increased between the 2 periods. Physicians and pharmacists can encourage patients to take advantage of the availability of influenza vaccines across various settings.

Estimating Vaccine Effectiveness Against Hospitalized Influenza During Pregnancy: Multicountry Protocol for a Retrospective Cohort Study

Background

Although pregnant women are believed to have elevated risks of severe influenza infection and are targeted for influenza vaccination, no study to date has examined influenza vaccine effectiveness (IVE) against laboratory-confirmed influenza-associated hospitalizations during pregnancy, primarily because this outcome poses many methodological challenges.

Objective

The Pregnancy Influenza Vaccine Effectiveness Network (PREVENT) was formed in 2016 as an international collaboration with the Centers for Disease Control and Prevention; Abt Associates; and study sites in Australia, Canada, Israel, and the United States. The primary goal of this collaboration is to estimate IVE in preventing acute respiratory or febrile illness (ARFI) hospitalizations associated with laboratory-confirmed influenza virus infection during pregnancy. Secondary aims include (1) describing the incidence, clinical course, and severity of influenza-associated ARFI hospitalization during pregnancy; (2) comparing the characteristics of ARFI-hospitalized pregnant women who were tested for influenza with those who were not tested; (3) describing influenza vaccination coverage in pregnant women; and (4) comparing birth outcomes among women with laboratory-confirmed influenza-associated hospitalization versus other noninfluenza ARFI hospitalizations.

Methods

For an initial assessment of IVE, sites identified a retrospective cohort of pregnant women aged from 18 to 50 years whose pregnancies overlapped with local influenza seasons from 2010 to 2016. Pregnancies were defined as those that ended in a live birth or stillbirth of at least 20 weeks gestation. The analytic sample for the primary IVE analysis was restricted to pregnant women who were hospitalized for ARFI during site-specific influenza seasons and clinically tested for influenza virus infection using real-time reverse transcription polymerase chain reaction.

Results

We identified approximately 2 million women whose pregnancies overlapped with influenza seasons; 550,344 had at least one hospitalization during this time. After restricting to women who were hospitalized for ARFI and tested for influenza, the IVE analytic sample included 1005 women.

Conclusions

In addition to addressing the primary question about the effectiveness of influenza vaccination, PREVENT data will address other important knowledge gaps including understanding the incidence, clinical course, and severity of influenza-related hospitalizations during pregnancy. The data infrastructure and international partnerships created for these analyses may be useful and informative for future influenza studies.

International Registered Report Identifier (IRRID)

DERR1-10.2196/11333

Vaccine effectiveness against laboratory-confirmed influenza hospitalizations among young children during the 2010-11 to 2013-14 influenza seasons in Ontario, Canada

Uncertainty remains regarding the magnitude of effectiveness of influenza vaccines for preventing serious outcomes, especially among young children. We estimated vaccine effectiveness (VE) against laboratory-confirmed influenza hospitalizations among children aged 6-59 months. We used the test-negative design in hospitalized children in Ontario, Canada during the 2010-11 to 2013-14 influenza seasons. We used logistic regression models adjusted for age, season, and time within season to calculate VE estimates by vaccination status (full vs. partial), age group, and influenza season. We also assessed VE incorporating prior history of influenza vaccination. We included specimens from 9,982 patient hospitalization episodes over four seasons, with 12.8% testing positive for influenza. We observed variation in VE by vaccination status, age group, and influenza season. For the four seasons combined, VE was 60% (95%CI, 44%-72%) for full vaccination and 39% (95%CI, 17%-56%) for partial vaccination. VE for full vaccination was 67% (95%CI, 48%-79%) for children aged 24-59 months, 48% (95%CI, 12%-69%) for children aged 6-23 months, 77% (95%CI, 47%-90%) for 2010-11, 59% (95%CI, 13%-81%) for 2011-12, 33% (95%CI, -18% to 62%) for 2012-13, and 72% (95%CI, 42%-86%) for 2013-14. VE in children aged 24-59 months appeared similar between those vaccinated in both the current and previous seasons and those vaccinated in the current season only, with the exception of 2012-13, when VE was lower for those vaccinated in the current season only. Influenza vaccination is effective in preventing pediatric laboratory-confirmed influenza hospitalizations during most seasons.