COVID-19 due to the B.1.617.2 (Delta) variant compared to B.1.1.7 (Alpha) variant of SARS-CoV-2: a prospective observational cohort study
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Abstract
The Delta (B.1.617.2) variant was the predominant UK circulating SARS-CoV-2 strain between May and December 2021. How Delta infection compares with previous variants is unknown. This prospective observational cohort study assessed symptomatic adults participating in the app-based COVID Symptom Study who tested positive for SARS-CoV-2 from May 26 to July 1, 2021 (Delta overwhelmingly the predominant circulating UK variant), compared (1:1, age- and sex-matched) with individuals presenting from December 28, 2020 to May 6, 2021 (Alpha (B.1.1.7) the predominant variant). We assessed illness (symptoms, duration, presentation to hospital) during Alpha- and Delta-predominant timeframes; and transmission, reinfection, and vaccine effectiveness during the Delta-predominant period. 3581 individuals (aged 18 to 100 years) from each timeframe were assessed. The seven most frequent symptoms were common to both variants. Within the first 28 days of illness, some symptoms were more common with Delta versus Alpha infection (including fever, sore throat, and headache) and some vice versa (dyspnoea). Symptom burden in the first week was higher with Delta versus Alpha infection; however, the odds of any given symptom lasting ≥ 7 days was either lower or unchanged. Illness duration ≥ 28 days was lower with Delta versus Alpha infection, though unchanged in unvaccinated individuals. Hospitalisation for COVID-19 was unchanged. The Delta variant appeared more (1.49) transmissible than Alpha. Re-infections were low in all UK regions. Vaccination markedly reduced the risk of Delta infection (by 69-84%). We conclude that COVID-19 from Delta or Alpha infections is similar. The Delta variant is more transmissible than Alpha; however, current vaccines showed good efficacy against disease. This research framework can be useful for future comparisons with new emerging variants.
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SciScore for 10.1101/2021.11.24.21266748: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Ethics IRB: Ethics approval was granted by the KCL Ethics Committee (LRS-19/20-18210).
Consent: At registration, all participants provided consent for their data to be used for COVID-19 research.Sex as a biological variable not detected. Randomization The COG-UK data are produced by sequencing a random sample of positive PCR tests from the general community. 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 …SciScore for 10.1101/2021.11.24.21266748: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Ethics IRB: Ethics approval was granted by the KCL Ethics Committee (LRS-19/20-18210).
Consent: At registration, all participants provided consent for their data to be used for COVID-19 research.Sex as a biological variable not detected. Randomization The COG-UK data are produced by sequencing a random sample of positive PCR tests from the general community. 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:We acknowledge the limitations of our observational study. Self-reported data from a mobile phone app may disproportionately represent more affluent populations and can introduce information bias and/or effect bias, although previous work from the CSS has shown that our self-reported data aligns well with surveys designed to be representative of the population.34 Participants could only report a positive test and we cannot confirm the actual variant causing infection, although our assumptions of Delta and Alpha infection are strongly supported by UK-COG surveillance variant testing. During the study, both overall numbers and individual app users fluctuated in their participation in the CSS-app, potentially for many factors including mass-media information, summer vacation, and perception of relevance. Our populations were matched for age and sex but not BMI; and we note higher diabetes prevalence and BMI in the Alpha cohort. Relevantly, vaccination was not only tiered by age but also to those with co-morbidities including diabetes. As mentioned, the timeframes of Alpha and Delta variant predominance differed with respect to guidance on social distancing and behavior in public spaces, highly likely to affect viral diffusion in the population, thus affecting our transmission calculations. Last, vaccine effectiveness could only be determined in tested individuals, noting that we do not have information regarding the reason for testing in these individuals. We were also only able...
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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