Transmission and containment of the SARS-CoV-2 Delta variant of concern in Guangzhou, China: A population-based study

PLoS Negl Trop Dis. 2022 Jan 5;16(1):e0010048. doi: 10.1371/journal.pntd.0010048. eCollection 2022 Jan.

Abstract

Background: The first community transmission of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Delta variant of concern (VOC) in Guangzhou, China occurred between May and June 2021. Herein, we describe the epidemiological characteristics of this outbreak and evaluate the implemented containment measures against this outbreak.

Methodology/principal findings: Guangzhou Center for Disease Control and Prevention provided the data on SARS-CoV-2 infections reported between 21 May and 24 June 2021. We estimated the incubation period distribution by fitting a gamma distribution to the data, while the serial interval distribution was estimated by fitting a normal distribution. The instantaneous effective reproductive number (Rt) was estimated to reflect the transmissibility of SARS-CoV-2. Clinical severity was compared for cases with different vaccination statuses using an ordinal regression model after controlling for age. Of the reported local cases, 7/153 (4.6%) were asymptomatic. The median incubation period was 6.02 (95% confidence interval [CI]: 5.42-6.71) days and the means of serial intervals decreased from 5.19 (95% CI: 4.29-6.11) to 3.78 (95% CI: 2.74-4.81) days. The incubation period increased with age (P<0.001). A hierarchical prevention and control strategy against COVID-19 was implemented in Guangzhou, with Rt decreasing from 6.83 (95% credible interval [CrI]: 3.98-10.44) for the 7-day time window ending on 27 May 2021 to below 1 for the time window ending on 8 June and thereafter. Individuals with partial or full vaccination schedules with BBIBP-CorV or CoronaVac accounted for 15.3% of the COVID-19 cases. Clinical symptoms were milder in partially or fully vaccinated cases than in unvaccinated cases (odds ratio [OR] = 0.26 [95% CI: 0.07-0.94]).

Conclusions/significance: The hierarchical prevention and control strategy against COVID-19 in Guangzhou was timely and effective. Authorised inactivated vaccines are likely to contribute to reducing the probability of developing severe disease. Our findings have important implications for the containment of COVID-19.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Basic Reproduction Number
  • COVID-19 / epidemiology*
  • COVID-19 / prevention & control*
  • COVID-19 / transmission
  • COVID-19 Vaccines / therapeutic use*
  • China / epidemiology
  • Communicable Disease Control / methods*
  • Female
  • Humans
  • Male
  • Middle Aged
  • Primary Prevention / methods
  • SARS-CoV-2 / isolation & purification*
  • Severity of Illness Index
  • Vaccination / statistics & numerical data
  • Young Adult

Substances

  • COVID-19 Vaccines

Supplementary concepts

  • COVID-19 breakthrough infections
  • SARS-CoV-2 variants

Grants and funding

This work was supported by National Natural Science Foundation of China [81973140, 82003555] to CQO and L LI, China Postdoctoral Science Foundation [2020M672744, 2020TQ0135] to L LI, the Key Project of Medicine Discipline of Guangzhou [2021–2023-11] to L LUO, and the Basic Research Project of Key Laboratory of Guangzhou [202102100001] to L LUO. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.