Transmission characteristics of SARS-CoV-2 variants of concern Rapid Scoping Review
Bibliographic record
Abstract
Abstract Background As of March 2021, three SARS-CoV-2 variants of concern (VOC) have been identified (B.1.1.7, B.1.351 and P.1) and been detected in over 111 countries. Despite their widespread circulation, little is known about their transmission characteristics. There is a need to understand current evidence on VOCs before practice and policy decisions can be made. This study aimed to map the evidence related to the transmission characteristics of three VOCs. Methods A rapid scoping review approach was used. Seven databases were searched on February 21, 2021 for terms related to VOCs, transmission, public health and health systems. A grey literature search was conducted on February 26, 2021. Title/abstracts were screened independently by one reviewer, while full texts were screened in duplicate. Data were extracted using a standardized form which was co-developed with infectious disease experts. A second data extractor verified the results. Studies were included if they reported on at least one of the VOCs and transmissibility. Animal studies and modeling studies were excluded. The final report was reviewed by content experts. Results Of the 1796 articles and 67 grey literature sources retrieved, 16 papers and 7 grey sources were included. Included studies used a wide range of designs and methods. The majority (n=20) reported on B.1.1.7. Risk of transmission, reported in 15 studies, was 45-71% higher for B.1.1.7 compared to non-VOCs, while R 0 was 75-78% higher and the reported R t ranged from 1.1-2.8. There was insufficient evidence on the transmission risk of B.1.35.1 and P.1. Twelve studies discussed the mechanism of transmission of VOCs. Evidence suggests an increase in viral load among VOCs based on cycle threshold values, and possible immune evasion due to increased ACE2 binding capacity of VOCs. However, findings should be interpreted with caution due to the variability in study designs and methods. Conclusion VOCs appear to be more transmissible than non-VOCs, however the mechanism of transmission is unclear. With majority of studies focusing on the B.1.1.7 VOC, more research is needed to build upon these preliminary findings. It is recommended that decision-makers continue to monitor VOCs and emerging evidence on this topic to inform public health policy.
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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 | 0.027 | 0.134 |
| Meta-epidemiology (narrow) | 0.002 | 0.001 |
| Meta-epidemiology (broad) | 0.007 | 0.007 |
| Bibliometrics | 0.037 | 0.025 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.006 | 0.006 |
| Open science | 0.002 | 0.003 |
| Research integrity | 0.003 | 0.002 |
| Insufficient payload (model declined to judge) | 0.008 | 0.001 |
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".