Single-Dose Messenger RNA Vaccine Effectiveness Against Severe Acute Respiratory Syndrome Coronavirus 2 in Healthcare Workers Extending 16 Weeks Postvaccination: A Test-Negative Design From Québec, Canada
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Abstract
Background
In Canada, first and second doses of messenger RNA (mRNA) vaccines against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) were uniquely spaced 16 weeks apart. We estimated 1- and 2-dose mRNA vaccine effectiveness (VE) among healthcare workers (HCWs) in Québec, Canada, including protection against varying outcome severity, variants of concern (VOCs), and the stability of single-dose protection up to 16 weeks postvaccination.
Methods
A test-negative design compared vaccination among SARS-CoV-2 test–positive and weekly matched (10:1), randomly sampled, test-negative HCWs using linked surveillance and immunization databases. Vaccine status was defined by 1 dose ≥14 days or 2 doses ≥7 days before illness onset or specimen collection. Adjusted VE was estimated by conditional logistic regression.
Results
Primary analysis included 5316 cases and 53 160 controls. Single-dose VE was 70% (95% confidence interval [CI], 68%–73%) against SARS-CoV-2 infection; 73% (95% CI, 71%–75%) against illness; and 97% (95% CI, 92%–99%) against hospitalization. Two-dose VE was 86% (95% CI, 81%–90%) and 93% (95% CI, 89%–95%), respectively, with no hospitalizations. VE was higher for non-VOCs than VOCs (73% Alpha) among single-dose recipients but not 2-dose recipients. Across 16 weeks, no decline in single-dose VE was observed, with appropriate stratification based upon prioritized vaccination determined by higher vs lower likelihood of direct patient contact.
Conclusions
One mRNA vaccine dose provided substantial and sustained protection to HCWs extending at least 4 months postvaccination. In circumstances of vaccine shortage, delaying the second dose may be a pertinent public health strategy.
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SciScore for 10.1101/2021.07.19.21260445: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Ethics IRB: It has been approved by the Research ethics board of the CHU de Québec-Université Laval. Sex as a biological variable not detected. Randomization To account for time-varying likelihoods of SARS-CoV-2 exposure and vaccination [15], a density sampling approach was used with 10 randomly-sampled controls per case matched by week of reference date. Blinding not detected. Power Analysis not detected. Table 2: Resources
No key resources detected.
Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).
Results from LimitationRecognizer: We detected the following sentences addressing limitations in …SciScore for 10.1101/2021.07.19.21260445: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Ethics IRB: It has been approved by the Research ethics board of the CHU de Québec-Université Laval. Sex as a biological variable not detected. Randomization To account for time-varying likelihoods of SARS-CoV-2 exposure and vaccination [15], a density sampling approach was used with 10 randomly-sampled controls per case matched by week of reference date. Blinding not detected. Power Analysis not detected. Table 2: Resources
No key resources detected.
Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).
Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:This study has limitations, foremost related to its observational design, subject to bias and confounding, and reliance on surveillance data subject to misclassification and missing information. Like others we could not fully adjust for differential exposure risk or fully ascertain the symptom profile notably after specimen testing. Despite easy access to testing, some asymptomatic infections were likely missed. HCWs with undetected infections before the study period could not be excluded leading to bias due to undiagnosed cases among vaccinated (overestimation) or unvaccinated (underestimation) participants [26]. A Ministerial order issued on April 9 requiring unvaccinated HCWs to be systematically tested every 3 days [27] may have increased detection of asymptomatic infections in unvaccinated individuals potentially leading to overestimation of VE against any infection at the end of the follow-up period but without affecting VE against COVID-19 or hospitalization. HCWs are active and relatively young adults and these results may not apply to older adults [28,29]. Even if adjustment for comorbidities did not change VE estimates, HCWs with medical conditions at high risk of severe disease were frequently removed from direct patient care duties during the pandemic and their VE might be lower than the estimates for all HCWs [22]. Despite these limitations, our study has strengths including its extended post-single-dose follow-up of a large and well-defined cohort and its severa...
Results from TrialIdentifier: No clinical trial numbers were referenced.
Results from Barzooka: We did not find any issues relating to the usage of bar graphs.
Results from JetFighter: We did not find any issues relating to colormaps.
Results from rtransparent:- Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
- Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
- No protocol registration statement was detected.
Results from scite Reference Check: We found no unreliable references.
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