After months of data collection, scientists agree: the Delta variant is the most contagious version of the coronavirus worldwide. It spreads about 225% faster than the original version of the virus, and it's currently dominating the outbreak in the United States, reports MedicalBrief.
A study, published online, sheds light on why. According to National Public Radio (NPR), It finds that the variant grows more rapidly inside people's respiratory tracts and to much higher levels, researchers at the Guangdong Provincial Center for Disease Control and Prevention reported.
On average, people infected with the Delta variant had about 1,000 times more copies of the virus in their respiratory tracts than those infected with the original strain of the coronavirus, the study found.
In addition, after someone catches the Delta variant, the person probably becomes infectious sooner. On average, it took about four days for the Delta variant to reach detectable levels inside a person, compared with six days for the original coronavirus variant.
In the study, scientists analysed COVID-19 patients involved in the first outbreak of the Delta variant in mainland China, which occurred between May 21 and June 18 in Guangzhou, the capital of Guangdong province. The researchers measured the levels of virus in 62 people involved in that outbreak and compared them with the levels in 63 patients infected in 2020 with an early version of the virus.
Their findings suggest that people who have contracted the Delta variant are probably spreading the virus earlier in the course of their infection.
And the scientists underscore the importance of quarantining immediately for 14 days after coming into contact with someone diagnosed with COVID-19, as the US Centers for Disease Control and Prevention recommends.
Or even better, getting fully vaccinated. Preliminary data shows that in some US states, 99.5% of COVID-19 deaths in the past few months were among people who weren't vaccinated, the CDC's director, Dr Rochelle Walensky, said.
"We know that the Delta variant … is currently surging in pockets of the country with low vaccination rates," she said. "We also know that our authorised vaccines prevent severe disease, hospitalisation and death from the Delta variant."
Study details
Viral infection and transmission in a large well-traced outbreak caused by the Delta SARS-CoV-2 variant
Baisheng Li, Aiping Deng, Kuibiao Li, Yao Hu, Zhencui Li, Qianling Xiong, Zhe Liu, Qianfang Guo, Lirong Zou, Huan Zhang,Meng Zhang, Fangzhu Ouyang, Juan Su, Wenzhe Su, Jing Xu, Huifang Lin, Jing Sun, Jingju Peng, Huiming Jiang, Pingping Zhou, Huanying Zhen, Jianpeng Xiao, Tao Liu, Rongfei Che, Hanri Zeng, Zhonghua Zheng, Yushi Huang, Jianxiang Yu, Lina Yi, Jie Wu, Jingdiao Chen, Haojie Zhong, Xiaoling Deng, Min Kang, Oliver G Pybus, Matthew Hall, Katrina A Lythgoe, Yan Li, Jun Yuan, Jianfeng He and Jing Lu.
Author affiliations: Guangdong Provincial Center for Disease Control and Prevention; Guangdong Workstation for Emerging Infectious Disease Control and Prevention, Chinese Academy of Medical Sciences; Guangzhou Center for Disease Control and Prevention; Guangdong Provincial Institution of Public Health; and the University of Oxford.
Published on Virological, a discussion forum for analysis and interpretation of virus molecular evolution and epidemiology, on 7 July 2021.
Summary
We report the first local transmission of the Delta SARS-CoV-2 variant in mainland China. All 167 infections could be traced back to the first index case. The investigation on daily sequential PCR testing of the quarantined subjects indicated the viral load of the first positive test of Delta infections was ~1000 times higher than that of the 19A/19B strains infections back in the initial epidemic wave of 2020, suggesting the potential faster viral replication rate and more infectiousness of the Delta variant at the early stage of the infection.
The 126 high-quality sequencing data and reliable epidemiological data indicated some minor intra-host single nucleotide variants (iSNVs) could be transmitted between hosts and finally fixed in the virus population during the outbreak. The minor iSNVs transmission between donor-recipient contribute at least 4 of 31 substitutions identified in the outbreak suggesting some iSNVs could quickly arise and reach fixation when the virus spread rapidly.
Disease control measures, including the frequency of population testing, quarantine in pre-symptomatic phase and enhancing the genetic surveillance should be adjusted to account for the increasing prevalence of the Delta variant at global level.
During the global spread of SARS-CoV-2, the genetic variants of the viruses emerged, and some have been proved to be more transmissible or could escape from the host immunity, which posed an increased risk to global public health1–3. An emerging genetic lineage, B.1.617, has been dominant in the largest outbreak of COVID-19 in India since March 2021, gaining global attention.
One sublineage, B.1.617.2, with spike protein mutations L452R, T478K and P681R, accounts for ~28% sequenced cases in Indian and rapidly replaced other lineages to become dominant in multiple regions and countries. The B.1.617.2 has been labeled as Variant of Concern (VOC), Delta. The virological profile of this VOC is needed to be urgently illustrated.
On May 21, 2021 the first local infection of the Delta variant in mainland China was identified. Similar to what has been done to the early epidemic in January 20205, strict interventions including population screen testing, activate contact tracing, and central quarantine/isolation have been carried out. However, in contrast to the restricted transmissions in 20205, a successive intergenerational transmission has been observed in the 2021 epidemic.
Here, we investigated the epidemiological, genetic, and serological data from this well-traced outbreak to characterize the virological profile of the Delta SARS-CoV-2 variant and discuss how the intervention strategies need to be improved on the racing against this emerging variant.
See more from MedicalBrief archives:
Delta variant may be transmitted in ‘scarily fleeting’ contacts
Face masks plus distancing increases COVID transmission control — Modelling study
Injected antibody cocktail cuts COVID-19 infection risk by over 80%