Comparative single-dose mRNA and ChAdOx1 vaccine effectiveness against SARS-CoV-2, including early variants of concern: a test-negative design, British Columbia, Canada
Bibliographic record
Abstract
ABSTRACT Introduction In randomized controlled trials, single-dose efficacy against SARS-CoV-2 illness exceeded 90% for mRNA vaccines (BNT162b2 and mRNA-1273), and 75% for ChAdOx1. In British Columbia (BC), Canada second doses were deferred up to 16 weeks and ChAdOx1 was only initially recommended for adults 55 years of age and older. We compared single-dose vaccine effectiveness (VE) during the spring 2021 wave in BC when Alpha and Gamma variants of concern (VOC) predominated. Methods VE was estimated against infection and hospitalization by test-negative design: cases were RT-PCR test-positive for SARS-CoV-2 and controls were test-negative. Adults 50-69 years old with specimen collection between April 4 and May 22 (weeks 14-20) were included. Variant-specific VE was estimated between weeks 17-20 when genetic characterization of all case viruses was performed, primarily through whole genome sequencing. Results VE analyses included 7,116 (10%) cases and 60,958 controls. Three-quarters of vaccinated participants received mRNA vaccine (60% BNT162b2, 15% mRNA-1273) and 25% received ChAdOx1. Half of genetically characterized viruses were Alpha, with 38% Gamma, 4% Delta and 8% non-VOCs. Single-dose VE against any infection was 75% (95%CI: 72-78) for BNT162b2, 82% (95%CI: 76-87) for mRNA-1273 and 61% (95%CI: 54-66) for ChAdOx1. VE against hospitalization was 83% (95%CI: 76-89), 85% (95%CI: 63-94) and 96% (95%CI: 86-99), respectively. VE against Alpha vs. Gamma infections did not differ among mRNA (78%;95%CI: 73-82 and 80%;95%CI: 74-85) or ChAdOx1 (66%;95%CI: 57-74 and 60%;95%CI: 48-69) recipients. Conclusions A single dose of mRNA vaccine reduced the SARS-CoV-2 infection risk by at least 75%, including infections due to early VOC. Although effectiveness of a single dose of ChAdOx1 was lower at 60% against infection, just one dose of any vaccine reduced the hospitalization risk by more than 80%. In the context of constrained vaccine supplies, these findings have implications for global vaccine deployment to reduce the overall burden of infections and hospitalizations due to SARS-CoV-2.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.010 | 0.008 |
| Meta-epidemiology (narrow) | 0.002 | 0.001 |
| Meta-epidemiology (broad) | 0.002 | 0.002 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.002 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.002 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".