Transmission dynamics and epidemiological characteristics of SARS-CoV-2 Delta variant infections in Guangdong, China, May to June 2021
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Abstract
The Delta variant of SARS-CoV-2 had become predominant globally by November 2021.
Aim
We evaluated transmission dynamics and epidemiological characteristics of the Delta variant in an outbreak in southern China.
Methods
Data on confirmed COVID-19 cases and their close contacts were retrospectively collected from the outbreak that occurred in Guangdong, China in May and June 2021. Key epidemiological parameters, temporal trend of viral loads and secondary attack rates were estimated. We also evaluated the association of vaccination with viral load and transmission.
Results
We identified 167 patients infected with the Delta variant in the Guangdong outbreak. Mean estimates of latent and incubation period were 3.9 days and 5.8 days, respectively. Relatively higher viral load was observed in infections with Delta than in infections with wild-type SARS-CoV-2. Secondary attack rate among close contacts of cases with Delta was 1.4%, and 73.1% (95% credible interval (CrI): 32.9–91.4) of the transmissions occurred before onset. Index cases without vaccination (adjusted odds ratio (aOR): 2.84; 95% CI: 1.19–8.45) or with an incomplete vaccination series (aOR: 6.02; 95% CI: 2.45–18.16) were more likely to transmit infection to their contacts than those who had received the complete primary vaccination series.
Discussion
Patients infected with the Delta variant had more rapid symptom onset compared with the wild type. The time-varying serial interval should be accounted for in estimation of reproduction numbers. The higher viral load and higher risk of pre-symptomatic transmission indicated the challenges in control of infections with the Delta variant.
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SciScore for 10.1101/2021.08.12.21261991: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
NIH rigor criteria are not applicable to paper type.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:Our study had several limitations. Self-reported symptom onset might bias estimates of the parameters, e.g., leading to an overestimation of the incubation period if patients tended to remember the later days with symptoms. Second, the Ct values used in our study were obtained from different diagnostic kits which shared the same …
SciScore for 10.1101/2021.08.12.21261991: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
NIH rigor criteria are not applicable to paper type.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:Our study had several limitations. Self-reported symptom onset might bias estimates of the parameters, e.g., leading to an overestimation of the incubation period if patients tended to remember the later days with symptoms. Second, the Ct values used in our study were obtained from different diagnostic kits which shared the same detection threshold but perhaps with different sensitivity and/or specificity. Finally, in estimation of the serial interval, transmission pairs with asymptomatic cases would be excluded due to absence of symptom onset dates, which however might have biased the estimates of the reproduction number by neglecting the impact of asymptomatic transmission. In conclusion, the Delta variant demonstrated a higher transmissibility compared to the wild type of SARS-CoV-2. An extension of contact tracing period to perhaps four days prior to symptom onset may be needed considering the high proportion of pre-symptomatic transmission and the high viral load before onset in infections with the Delta variant. Inactivated vaccines appeared to be effective in reducing transmission of Delta infections and a high vaccination coverage should be pursued to reduce the burden of COVID-19 pandemic.
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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