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Transmission Dynamics of an Outbreak of the COVID-19 Delta Variant B.1.617.2 – Guangdong Province, China, May – June 2021
Abstract and Figures
The number of infections has increased rapidly following the first case and led to 5 generations of transmission in 10 days.
We investigated the key transmission parameters for this outbreak. The result showed that the mean incubation period was 4.4 days which was shorter than that reported by Li et al. (4.4 vs. 5.2) in Wuhan City, Hubei Province, China. The mean generation time was 2.9 days, which was much shorter than that reported by Hu et al. in Hunan Province (2.9 vs. 5.7). The mean serial interval was 2.3 days, which was also shorter than that reported by previous reports. We observed that 64.7% (44/68) of transmission events occurred during the pre-symptomatic phase.
The estimated R0 was 3.2 (95% CI: 2.0–4.8), which was much higher than 2.2 from Li et al. (2). Based on the GT and R0 estimated, the epidemic growth rate for the early stage of the outbreak was about 100% higher than findings from previous epidemic strains.
In this epidemic, the Rt increased from 3.0 to 3.5 from May 27 to May 29, then decreased after May 30, reached a value of 1 on June 6, and fluctuated near 1 from June 7 to June 15. The Rt was lower than 1 from June 16, and there were no new cases reported from June 19 to June 23. To respond to the unprecedented threat, Guangdong Province has taken a series of rigorous intervention measures including mass testing, active cases finding, community management, travel restrictions, and affected area lockdown to contain this outbreak. The evidence indicated that the public health measures taken by Guangdong have had an effect on the epidemic.
In conclusion, we observed that the transmission of this COVID-19 outbreak in Guangdong was faster and more severe than that of previous epidemics.
http://weekly.chinacdc.cn/en/article/doi/10.46234/ccdcw2021.148
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... The COVID-19 epidemic has been ongoing since the WHO declared the pandemic on March 11, 2020, and a highly transmissible Delta variant was identified in late May 2021 in Guangdong Province, China 45 . Studies have shown that inactivated vaccines effectively reduce Delta transmission, with no deaths reported in Guangdong until June 18, 2021, emphasizing the importance of widespread vaccination 46 . ...
COVID-19 survivors concerning about the rehabilitation and sustained sequelae of Coronavirus Disease 2019 (COVID-19) infection. We aimed to investigate the sequelae of patients’ psychological and physical condition and its related factors in the early and late stages. This longitudinal study tracked 281 COVID-19 patients discharged from hospitals in Guangdong, China, for one year. Assessments occurred at 2,4,12,24 and 48 weeks post-discharge. We define 2 weeks, 4 weeks, and 12 weeks as early stage, and 24 weeks and 48 weeks as late stage. Psychological health was measured using the Patient Health Questionnaire-9 (PHQ-9), Generalized Anxiety Disorder-7 (GAD-7), Posttraumatic Stress Disorder Checklist for DSM-5 (PCL-5), and Pittsburgh Sleep Quality Index (PSQI) scales. Physical health was assessed through laboratory tests, chest computed tomography (CT) scans, and pulmonary function tests. Data were analyzed using multivariate regression models to evaluate the influence of demographic and clinical variables on health outcomes. COVID-19 survivors exhibited psychological and physical sequelae in both the early and late stages. Compared to the early stage, the proportions of patients with depression (early stage 14.6%, late stage 4.6%), anxiety (early stage 8.9%, late stage 5.3%), PTSD(early stage 3.6%, late stage 0.7%), abnormal liver function (early stage 24.6%, late stage 11.0%), abnormal cardiac function (early stage 10.0%, late stage 7.8%), abnormal renal function (early stage 20.6%, late stage 11.0%) and abnormal pulmonary function (early stage 40.9%, late stage 13.5%) were significantly reduced in the late stage. Factors such as gender, age, severity of COVID-19, hospitalization duration, and various comorbidities were significantly associated with these sequelae. We noticed that psychological and physical sequelae occurred to COVID-19 survivors in short and long stages, and these would gradually decrease as time went on. Male gender, age > 50 years old, severe clinical condition, longer hospitalization time and comorbidity history were related factors that significantly affected the rehabilitation of COVID-19 patients.
... These are listed in Table 1 (those labeled as fitted). In addition, the migrations rates of the population between districts (τ ij ) are estimated using a gravity model [60] and the only unknown parameter in the expression for τ ij is D in (5), please see the detailed description of the estimation process in section 1 of S1 Appendix. The new cases in district i on day t is thus ...
Non-pharmaceutical interventions (NPIs) are effective in mitigating infections during the early stages of an infectious disease outbreak. However, these measures incur significant economic and livelihood costs. To address this, we developed an optimal control framework aimed at identifying strategies that minimize such costs while ensuring full control of a cross-regional outbreak of emerging infectious diseases. Our approach uses a spatial SEIR model with interventions for the epidemic process, and incorporates population flow in a gravity model dependent on gross domestic product (GDP) and geographical distance. We applied this framework to identify an optimal control strategy for the COVID-19 outbreak caused by the Delta variant in Xi’an City, Shaanxi, China, between December 2021 and January 2022. The model was parameterized by fitting it to daily case data from each district of Xi’an City. Our findings indicate that an increase in the basic reproduction number, the latent period or the infectious period leads to a prolonged outbreak and a larger final size. This indicates that diseases with greater transmissibility are more challenging and costly to control, and so it is important for governments to quickly identify cases and implement control strategies. Indeed, the optimal control strategy we identified suggests that more costly control measures should be implemented as soon as they are deemed necessary. Our results demonstrate that optimal control regimes exhibit spatial, economic, and population heterogeneity. More populated and economically developed regions require a robust regular surveillance mechanism to ensure timely detection and control of imported infections. Regions with higher GDP tend to experience larger-scale epidemics and, consequently, require higher control costs. Notably, our proposed optimal strategy significantly reduced costs compared to the actual expenditures for the Xi’an outbreak.
... During the periods of more severe situations such as Stage 1 and Stage 5, stricter strategies of a level 1 emergency response and the dynamic zero-COVID strategy were timely taken. In May 2021, the SARS-CoV-2 Delta variant first appeared in Guangdong, China and contributed to the local epidemic in Guangzhou and Shenzhen [14,42]. In December 2021, the Omicron virus first appeared in Guangdong demonstrating a higher transmission rate than the Delta variant, resulting in a broader spread and increased infections [43]. ...
Background
From January 2020 to June 2022, strict interventions against COVID-19 were implemented in Guangdong Province, China. However, the evolution of COVID-19 dynamics remained unclear in this period.
Objectives
This study aims to investigate the evolution of within- and between-city COVID-19 dynamics in Guangdong, specifically during the implementation of rigorous prevention and control measures. The intent is to glean valuable lessons that can be applied to refine and optimize targeted interventions for future crises.
Methods
Data of COVID-19 cases and synchronous interventions from January 2020 to June 2022 in Guangdong Province were collected. The epidemiological characteristics were described, and the effective reproduction number (Rt) was estimated using a sequential Bayesian method. Endemic-epidemic multivariate time-series model was employed to quantitatively analyze the spatiotemporal component values and variations, to identify the evolution of within- and between-city COVID-19 dynamics.
Results
The incidence of COVID-19 in Guangdong Province was 12.6/100,000 population (15,989 cases) from January 2020 to June 2022. The Rt predominantly remained below 1 and increased to a peak of 1.39 in Stage 5. As for the evolution of variations during the study period, there were more spatiotemporal components in stage 1 and 5. All components were fewer from Stage 2 to Stage 4. Results from the endemic-epidemic multivariate time-series model revealed a strong follow-up impact from previous infections in Dongguan, Guangzhou and Zhanjiang, with autoregressive components of 0.48, 0.45 and 0.36, respectively. Local risk was relatively high in Yunfu, Shanwei and Shenzhen, with endemic components of 1.17, 1.04 and 0.71, respectively. The impact of the epidemic on the neighboring regions was significant in Zhanjiang, Shenzhen and Zhuhai, with epidemic components of 2.14, 1.92, and 1.89, respectively.
Conclusion
The findings indicate the presence of spatiotemporal variation of COVID-19 in Guangdong Province, even with the implementation of strict interventions. It’s significant to prevent transmissions within cities with dense population. Preventing spatial transmissions between cities is necessary when the epidemic is severe. To better cope with future crises, interventions including vaccination, medical resource allocation and coordinated non-pharmaceutical interventions were suggested.
Supplementary Information
The online version contains supplementary material available at 10.1186/s13690-024-01406-1.
Background
Coronavirus disease 2019 is caused by the severe acute respiratory syndrome coronavirus 2, which has become a pandemic. Severe acute respiratory syndrome coronavirus 2 is an enveloped, unsegmented, positive‐sense, single‐stranded RNA virus that belongs to the family Coronaviridae.
Aim
The objective of this review is to conduct a qualitative analysis of the current updates on epidemiology, evolution, and vaccine variants for SARS‐CoV‐2.
Method
The search strategy was done from the database based on the PRISMA criteria for qualitative analysis of this review. Literature on variants of severe acute respiratory syndrome coronavirus 2, published in English in the last 5 years (2019–2023), were included. From 179 a total of 105 articles were reviewed, searched, and retrieved from the electronic databases PubMed. The search was done using keywords like COVID‐19, SARS‐CoV‐2, variants, mutations, and vaccines, and articles were managed using EndNote X8 software. The scope of view for this review was the course of the pandemic by emerging variants and how man is struggling to overcome this sudden pandemic through vaccines. The narrative skeleton was constructed based on the article's scope of view.
Result
From the parent severe acute respiratory syndrome coronavirus 2, many variants emerged during the course of this pandemic. They are mainly categorized into two variants: variants of interest and variants of concern based on the impact on public health. The World Health Organization leveled five variants: Alpha (strain B.1.1.7), Beta (strain B.1.351), Gamma (strain P.1), Delta (strain B.1.617.2), and Omicron (B.1.1.529).
Conclusions
It is crucial to stay informed about the latest developments in the understanding of SARS‐CoV‐2 variants, as new variants can emerge and impact the course of the pandemic. Health authorities and researchers continuously have to monitor and study these variants to assess their characteristics, transmissibility, severity, and the effectiveness of vaccines against them. One has to always refer to the latest information from reputable health journals or organizations for the most up‐to‐date and accurate details on COVID‐19 variants.
BACKGROUND
Pregnant individuals have faced unique challenges during the COVID-19 pandemic, necessitating a closer examination of maternal and fetal health outcomes.
OBJECTIVES
Investigate the morbidity and mortality associated with SARS-CoV-2 infection among pregnant individuals, considering vaccination status and variant strains.
DESIGN
Retrospective cohort
SETTING
Tertiary state hospital
PATIENTS AND METHODS
Patients who underwent cesarean sections were categorized into three periods: pre-vaccination (before 31 August 2021), early post-vaccination (from September 2021), and late post-vaccination (aligned with 70% immunization coverage by 2 September 2021). Data collected included demographic information (age, gravidity, parity count, gestational age, newborn APGAR scores), cesarean section indications, chronic diseases, vaccination status, vaccine type and doses, SARS-CoV-2 variant status, ICU admission, and mortality due to COVID-19.
MAIN OUTCOME MEASURES
ICU admission and mortality rates, focusing on the impact of SARS-CoV-2 infection and vaccination status.
SAMPLE SIZE
297 COVID PCR-positive symptomatic patients who underwent cesarean sections.
RESULTS
In the pre-vaccination group, there were 13 mortalities (8.1%) compared to 9 (6.6%) post-vaccination ( P =.610). Maternal ARDS was seen in 46.2% of pre-vaccination mortalities versus 11.1% post-vaccination ( P =.045). COVID-19 delta variant patients had higher ICU admission (80%) and mortality rates (40%). Rates of COVID-19 PCR-positive cesarean sections, ICU admissions, and mortality declined significantly in early ( P =.021, P =.004, P =.009), respectively and late post-vaccination periods ( P <.001, P <.001, P =.0019), respectively. Vaccinated patients had no ICU admissions or mortality.
CONCLUSIONS
Vaccination against COVID-19 is crucial for pregnant individuals as it significantly reduces the risk of severe illness. While vaccines offer substantial protection, the pandemic’s acute phase might be waning, yet COVID-19 remains a global threat, particularly in regions with limited vaccine access. Continued vigilance and proactive measures are essential to mitigate ongoing risks and the emergence of new variant strains.
LIMITATIONS
Retrospective observational design and the single-center setting, which may affect the generalizability of the findings.
We constructed a rapid infection risk assessment model for contacts of COVID‐19. The improved Wells–Riley model was used to estimate the probability of infection for contacts of COVID‐19 in the same place and evaluate their risk grades. We used COVID‐19 outbreaks that were documented to validate the accuracy of the model. We analyzed the relationship between controllable factors and infection probability and constructed common scenarios to analyze the infection risk of contacts in different scenarios. The model showed the robustness of the fitting (mean relative error = 5.89%, mean absolute error = 2.03%, root mean squared error = 2.03%, R² = 0.991). We found that improving ventilation from poorly ventilated to naturally ventilated and wearing masks can reduce the probability of infection by about two times. Contacts in places of light activity, loud talking or singing, and heavy exercise, oral breathing (e.g., gyms, KTV, choirs) were at higher risk of infection. The model constructed in this study can quickly and accurately assess the infection risk grades of COVID‐19 contacts. Simply opening doors and windows for ventilation can significantly reduce the risk of infection in certain places. The places of light activity, loud talking or singing, and heavy exercise, oral breathing, should pay more attention to prevent and control transmission of the epidemic.
We present a global analysis of the spread of recently emerged SARS-CoV-2 variants and estimate changes in effective reproduction numbers at country-specific level using sequence data from GISAID. Nearly all investigated countries demonstrated rapid replacement of previously circulating lineages by the World Health Organization-designated variants of concern, with estimated transmissibility increases of 29% (95% CI: 24–33), 25% (95% CI: 20–30), 38% (95% CI: 29–48) and 97% (95% CI: 76–117), respectively, for B.1.1.7, B.1.351, P.1 and B.1.617.2.
Several mechanisms driving SARS-CoV-2 transmission remain unclear. Based on individual records of 1178 potential SARS-CoV-2 infectors and their 15,648 contacts in Hunan, China, we estimated key transmission parameters. The mean generation time was estimated to be 5.7 (median: 5.5, IQR: 4.5, 6.8) days, with infectiousness peaking 1.8 days before symptom onset, with 95% of transmission events occurring between 8.8 days before and 9.5 days after symptom onset. Most transmission events occurred during the pre-symptomatic phase (59.2%). SARS-CoV-2 susceptibility to infection increases with age, while transmissibility is not significantly different between age groups and between symptomatic and asymptomatic individuals. Contacts in households and exposure to first-generation cases are associated with higher odds of transmission. Our findings support the hypothesis that children can effectively transmit SARS-CoV-2 and highlight how pre-symptomatic and asymptomatic transmission can hinder control efforts.
Objectives
We aimed to estimate the time-varying transmission dynamics of COVID-19 in China, Wuhan City and Guangdong province, and compared them with that of severe acute respiratory syndrome (SARS).
Methods
Data on COVID-19 cases by March 20, 2020 in China was collected from epidemiological investigations or official websites. Data on SARS cases in Guangdong Province, Beijing and Hong Kong during 2002-2003 were also obtained. We estimated the doubling time, basic reproduction number (R0) and time-varying reproduction number (Rt) of COVID-19 and SARS.
Results
As of March 20, 2020, 80,739 COVID-19 indigenous cases were identified in mainland China. Most cases were reported between January 20 and February 29. The R0 of COVID-19 nationwide and in Wuhan were 5.0 and 4.8 respectively, which were greater than R0 of SARS in Guangdong (R0=2.3), Hong Kong (R0 = 2.3), and Beijing (R0 = 2.6). During the epidemic of COVID-19, the Rt nationwide first increased to a peak of 8.4 and declined quickly to below 1 in one month. In terms of SARS, the Rt curve saw a fluctuation change with more than one peak though the peak was lower than COVID-19.
Conclusions
COVID-19 has much higher transmissibility than SARS, and a series of major actions for suppressing the outbreak are effective. However, persistent efforts are needed to prevent the rebound of the epidemic in the context of the global pandemic.
Importance
Coronavirus disease 2019 (COVID-19) has become a pandemic, and it is unknown whether a combination of public health interventions can improve control of the outbreak.
Objective
To evaluate the association of public health interventions with the epidemiological features of the COVID-19 outbreak in Wuhan by 5 periods according to key events and interventions.
Design, Setting, and Participants
In this cohort study, individual-level data on 32 583 laboratory-confirmed COVID-19 cases reported between December 8, 2019, and March 8, 2020, were extracted from the municipal Notifiable Disease Report System, including patients’ age, sex, residential location, occupation, and severity classification.
Exposures
Nonpharmaceutical public health interventions including cordons sanitaire, traffic restriction, social distancing, home confinement, centralized quarantine, and universal symptom survey.
Main Outcomes and Measures
Rates of laboratory-confirmed COVID-19 infections (defined as the number of cases per day per million people), across age, sex, and geographic locations were calculated across 5 periods: December 8 to January 9 (no intervention), January 10 to 22 (massive human movement due to the Chinese New Year holiday), January 23 to February 1 (cordons sanitaire, traffic restriction and home quarantine), February 2 to 16 (centralized quarantine and treatment), and February 17 to March 8 (universal symptom survey). The effective reproduction number of SARS-CoV-2 (an indicator of secondary transmission) was also calculated over the periods.
Results
Among 32 583 laboratory-confirmed COVID-19 cases, the median patient age was 56.7 years (range, 0-103; interquartile range, 43.4-66.8) and 16 817 (51.6%) were women. The daily confirmed case rate peaked in the third period and declined afterward across geographic regions and sex and age groups, except for children and adolescents, whose rate of confirmed cases continued to increase. The daily confirmed case rate over the whole period in local health care workers (130.5 per million people [95% CI, 123.9-137.2]) was higher than that in the general population (41.5 per million people [95% CI, 41.0-41.9]). The proportion of severe and critical cases decreased from 53.1% to 10.3% over the 5 periods. The severity risk increased with age: compared with those aged 20 to 39 years (proportion of severe and critical cases, 12.1%), elderly people (≥80 years) had a higher risk of having severe or critical disease (proportion, 41.3%; risk ratio, 3.61 [95% CI, 3.31-3.95]) while younger people (<20 years) had a lower risk (proportion, 4.1%; risk ratio, 0.47 [95% CI, 0.31-0.70]). The effective reproduction number fluctuated above 3.0 before January 26, decreased to below 1.0 after February 6, and decreased further to less than 0.3 after March 1.
Conclusions and Relevance
A series of multifaceted public health interventions was temporally associated with improved control of the COVID-19 outbreak in Wuhan, China. These findings may inform public health policy in other countries and regions.
Background:
The initial cases of novel coronavirus (2019-nCoV)-infected pneumonia (NCIP) occurred in Wuhan, Hubei Province, China, in December 2019 and January 2020. We analyzed data on the first 425 confirmed cases in Wuhan to determine the epidemiologic characteristics of NCIP.
Methods:
We collected information on demographic characteristics, exposure history, and illness timelines of laboratory-confirmed cases of NCIP that had been reported by January 22, 2020. We described characteristics of the cases and estimated the key epidemiologic time-delay distributions. In the early period of exponential growth, we estimated the epidemic doubling time and the basic reproductive number.
Results:
Among the first 425 patients with confirmed NCIP, the median age was 59 years and 56% were male. The majority of cases (55%) with onset before January 1, 2020, were linked to the Huanan Seafood Wholesale Market, as compared with 8.6% of the subsequent cases. The mean incubation period was 5.2 days (95% confidence interval [CI], 4.1 to 7.0), with the 95th percentile of the distribution at 12.5 days. In its early stages, the epidemic doubled in size every 7.4 days. With a mean serial interval of 7.5 days (95% CI, 5.3 to 19), the basic reproductive number was estimated to be 2.2 (95% CI, 1.4 to 3.9).
Conclusions:
On the basis of this information, there is evidence that human-to-human transmission has occurred among close contacts since the middle of December 2019. Considerable efforts to reduce transmission will be required to control outbreaks if similar dynamics apply elsewhere. Measures to prevent or reduce transmission should be implemented in populations at risk. (Funded by the Ministry of Science and Technology of China and others.).
Key questions remain about how quickly B.1.617 variants can spread, their potential to evade immunity and how they might affect the course of the pandemic. Key questions remain about how quickly B.1.617 variants can spread, their potential to evade immunity and how they might affect the course of the pandemic.
Background
Several parameters driving the transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) remain unclear, including age-specific differences in infectivity and susceptibility, and the contribution of inapparent infections to transmission. Robust estimates of key time-to-event distributions remain scarce as well.
Methods
We collected individual records for 1,178 SARS-CoV-2 infected individuals and their 15,648 contacts identified by contact tracing and monitoring over the period from January 13 to April 02, 2020 in Hunan Province, China. We provide descriptive statistics of the characteristics of cases and their close contacts; we fitted distributions to time-to-key-events distributions and infectiousness profile over time; and we used generalized linear mixed model to estimate risk factors for susceptibility and transmissibility of SARS-CoV-2.
Results
We estimated the mean serial interval at 5.5 days (95%CI −5.0, 19.9) and the mean generation time at 5.5 days (95%CI 1.7, 11.6). The infectiousness was estimated to peak 1.8 days before symptom onset, with 95% of transmission events occurring between 7.6 days before and 7.3 days after the date of symptom onset. The proportion of pre-symptomatic transmission was estimated to be 62.5%. We estimated that at least 3.5% of cases were generated asymptomatic individuals. SARS-CoV-2 transmissibility was not significantly different between working-age adults (15-59 years old) and other age groups (0-14 years old: p-value=0.16; 60 years and over: p-value=0.33), whilst susceptibility to SARS-CoV-2 infection was estimated to increase with age (p-value=0.03). In addition, transmission risk was higher for household contacts (p-value<0.001), decreased for higher generations within a cluster (second generation: odds ratio=0.13, p-value<0.001; generations 3-4: odds ratio=0.05, p-value<0.001, relative to generation 1), and decreased for infectors with a larger number of contacts (p-value=0.04).
Interpretation
Our findings warn of the possible relevant contribution of children to SARS-CoV-2 transmission. When lockdown interventions are in place, we found that odds of transmission are highest in the household setting but, with the relaxation of interventions, other settings (including schools) could bear a higher risk of transmission. Moreover, the estimated relevant fraction of pre-symptomatic and asymptomatic transmission highlight the importance of large-scale testing, contact tracing activities, and the use of personnel protective equipment during the COVID-19 pandemic.