Single-dose mRNA Vaccine Effectiveness Against Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), Including Alpha and Gamma Variants: A Test-negative Design in Adults 70 Years and Older in British Columbia, Canada
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Abstract
Background
Randomized-controlled trials of messenger RNA (mRNA) vaccine protection against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) included relatively few elderly participants. We assess single-dose mRNA vaccine effectiveness (VE) in adults ≥ 70 years old in British Columbia, Canada, where second doses were deferred by up to 16 weeks and where a spring 2021 wave uniquely included codominant circulation of Alpha (B.1.1.7) and Gamma (P.1) variants of concern (VOC).
Methods
Analyses included community-dwelling adults ≥ 70 years old with specimen collection between 4 April (epidemiological week 14) and 1 May (week 17) 2021. Adjusted VE was estimated by test-negative design. Cases were reverse-transcription polymerase chain reaction (RT-PCR) test-positive for SARS-CoV-2, and controls were test-negative. Vaccine status was defined by receipt of a single-dose ≥ 21 days before specimen collection, but a range of intervals was assessed. Variant-specific VE was estimated against viruses genetically characterized as Alpha, Gamma or non-VOC lineages.
Results
VE analyses included 16 993 specimens: 1226 (7%) test-positive cases and 15 767 test-negative controls. Of 1131 (92%) genetically characterized viruses, 509 (45%), 314 (28%), and 276 (24%) were Alpha, Gamma, and non-VOC lineages, respectively. At 0–13 days postvaccination, VE was negligible at 14% (95% confidence interval [CI], 0–26) but increased from 43% (95% CI, 30–53) at 14–20 days to 75% (95% CI, 63–83) at 35–41 days postvaccination. VE at ≥ 21 days postvaccination was 65% (95% CI, 58–71) overall: 72% (95% CI, 58–81), 67% (95% CI, 57–75), and 61% (95% CI, 45–72) for non-VOC, Alpha, and Gamma variants, respectively.
Conclusions
A single dose of mRNA vaccine reduced the risk of SARS-CoV-2 by about two-thirds in adults ≥ 70 years old, with protection only minimally reduced against Alpha and Gamma variants.
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SciScore for 10.1101/2021.06.07.21258332: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Ethics IRB: Ethics statement: Data linkages and analyses were conducted under a surveillance mandate, authorized by the Provincial Health Officer under the Public Health Act, and exempt from research ethics board review. Sex as a biological variable Source population, analysis period and study design: There are about 673,000 adults ≥70-years-old in BC (13% of the total 5.1 million population) including ∼437,000 (65%) 70-79 years, 188,000 (28%) 80-89 years and 48,000 (7%) ≥90 years old with slightly more than half who are women (54%) [8]. Randomization In an alternative individual-based approach, only one randomly-selected negative specimen per individual could contribute. Blinding not detected. Power … SciScore for 10.1101/2021.06.07.21258332: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Ethics IRB: Ethics statement: Data linkages and analyses were conducted under a surveillance mandate, authorized by the Provincial Health Officer under the Public Health Act, and exempt from research ethics board review. Sex as a biological variable Source population, analysis period and study design: There are about 673,000 adults ≥70-years-old in BC (13% of the total 5.1 million population) including ∼437,000 (65%) 70-79 years, 188,000 (28%) 80-89 years and 48,000 (7%) ≥90 years old with slightly more than half who are women (54%) [8]. Randomization In an alternative individual-based approach, only one randomly-selected negative specimen per individual could contribute. 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:The main limitation of our analysis, as elsewhere, is our reliance on general laboratory submissions and clinical or surveillance data that were originally collected for a different purpose and are subject to missing information and misclassification, as well as selection bias. Although foremost symptom-based, the clinical testing indications for COVID-19 are broad, discretionary and variable. To attempt standardization of the likelihood of test-positivity among sampled specimens we excluded those identified as having been collected from congregate settings or for non-clinical screening purposes. Such exclusions, however, may have been incomplete or introduced other unintended biases. We were limited in the covariates we could include in our model and cannot rule out residual bias and confounding. As a form of validity check, we assessed VE during the 0-13-day period when little or no vaccine effect is anticipated, confirming negligible VE as expected. For similar reasons, we compared vaccine coverage and other characteristics of our test-negative controls to that of the general source population ≥70-years-old in BC, and this was reassuringly concordant. Our findings also align well with other observational studies in older adults each of which are, however, subject to similar issues. Because the PLOVER database from which we sampled does not reliably capture symptoms or onset dates, we assessed VE against any infection without symptom or severity specification. VE estimates ...
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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