Objectives To estimate the marginal effectiveness of a fourth versus third dose and the vaccine effectiveness of mRNA covid-19 vaccines BNT162b2 and mRNA-1273 against any infection, symptomatic infection, and severe outcomes (hospital admission or death) related to the omicron variant. Design Test negative design. Setting Long term care facilities in Ontario, Canada, 30 December 2021 to 27 April 2022. Participants After exclusions, 61 344 residents aged 60 years or older across 626 long term care facilities in Ontario, Canada who were tested for SARS-CoV-2 were included. Main outcome measures Laboratory confirmed omicron SARS-CoV-2 infection (any and symptomatic) by reverse transcription polymerase chain reaction (RT-PCR), and hospital admission or death. Multivariable logistic regression was used to estimate marginal effectiveness (four versus three doses) and vaccine effectiveness (two, three, or four doses versus no doses) while adjusting for personal characteristics, comorbidities, week of test, and previous positive SARS-CoV-2 test result more than 90 days previously. Results 13 654 residents who tested positive for omicron SARS-CoV-2 infection and 205 862 test negative controls were included. The marginal effectiveness of a fourth dose (95% of vaccine recipients received mRNA-1273 as the fourth dose) seven days or more after vaccination versus a third dose received 84 or more days previously was 19% (95% confidence interval 12% to 26%) against infection, 31% (20% to 41%) against symptomatic infection, and 40% (24% to 52%) against severe outcomes. Vaccine effectiveness in vaccine recipients (compared with unvaccinated) increased with each additional dose, and for a fourth dose was 49% (95% confidence interval 43% to 54%) against infection, 69% (61% to 76%) against symptomatic infection, and 86% (81% to 90%) against severe outcomes. Conclusions The findings suggest that compared with a third dose of mRNA covid-19 vaccine, a fourth dose improved protection against infection, symptomatic infection, and severe outcomes among long term care residents during an omicron dominant period. A fourth vaccine dose was associated with strong protection against severe outcomes in vaccinated residents compared with unvaccinated residents, although the duration of protection remains unknown.

Increasing opioid prescribing has been linked to an epidemic of opioid misuse. Our objective is to synthesize the available evidence about patient-, prescriber-, medication-, and system-level risk factors for developing misuse among patients prescribed opioids for noncancer pain.Methods: We performed a systematic search of the scientific and gray literature for studies reporting on risk factors for prescription opioid misuse. Two reviewers independently reviewed titles, abstracts, and full texts; extracted data; and assessed study quality. We excluded studies with greater than 50% cancer patients, palliative patients, and illicit opioid initiation. When possible, we synthesized the effect sizes of dichotomous risk factors and their associations with opioid misuse, using inversevariance random-effects meta-analysis. We calculated the mean difference between opioid misusers and nonmisusers for continuous risk factors. When studies lacked homogeneity, we synthesized their results qualitatively.Results: Of 9,629 studies, 65 met our inclusion criteria. Among patients with outpatient opioid prescriptions, the following factors were associated with the development of misuse: any current or previous substance use (odds ratio [OR] 3.55; 95% confidence interval [CI] 2.62 to 4.82), any mental health diagnosis (OR 2.45; 95% CI 1.91 to 3.15), younger age (OR 2.19; 95% CI 1.81 to 2.64), and male sex (OR 1.23; 95% CI 1.10 to 1.36). Conclusion:Although clinicians should endeavor to offer alternative pain management strategies to all patients, those who are younger, are male patients, and report a history of or current substance use or mental health diagnoses were associated with a greater risk of developing opioid misuse. Clinicians should consider prioritizing alternative pain management strategies for these higher-risk patients.

This cross-sectional study quantifies the added burden of fatal opioid overdoses during the first 6 months of the COVID-19 pandemic in Ontario, Canada.

Key PointsQuestionAmong recipients of opioid agonist therapy (OAT) in Ontario, Canada, early in the COVID-19 pandemic, was there an association between dispensing of increased take-home doses and treatment retention or opioid-related harm?FindingsIn this retrospective propensity-weighted cohort study of 21 297 OAT recipients stratified by baseline dosing and type of OAT, dispensing of increased take-home doses of OAT, compared with no change in take-home doses, was significantly associated with lower rates of OAT interruption and discontinuation in most subsets, with no statistically significant increases in opioid overdoses over 6 months of follow-up.MeaningIn Ontario, Canada, during the COVID-19 pandemic, dispensing of increased take-home doses of OAT was significantly associated with lower rates of treatment interruption and discontinuation among some subsets of patients, and there were no statistically significant increases in opioid-related overdoses, although the findings may be susceptible to residual confounding and should be interpreted cautiously.

Background: London InterCommunity Health Centre (LIHC) launched a safer opioid supply (SOS) program in 2016, where clients are prescribed pharmaceutical opioids and provided with comprehensive health and social supports. We sought to evaluate the impact of this program on health services utilization and health care costs.