Chinese scientists detail Delta variant transmission chain

Report shows shorter incubation period and higher viral load for the new strain

With the Delta variant of the novel coronavirus fast becoming the dominant strain in many countries, Chinese scientists recently published a report believed to be the first to thoroughly describe the whole chain of the transmission of the variant, the kinetics of the viral load and the clinical characteristics in a local outbreak.

The report was compiled by scientists from institutions such as the Guangzhou Eighth People's Hospital and the Guangzhou Institute of Respiratory Health of The First Affiliated Hospital of Guangzhou Medical University, including Zhong Nanshan, a leading Chinese respiratory disease researcher.

It was published on Sunday in EClinicalMedicine of The Lancet, a medical journal.

By studying the 159 people infected with the Delta variant in an outbreak in Guangzhou, Guangdong province, between May 21 and June 18, the scientists found seven transmission generations, including four generations in the first 10 days.

A 75-year-old woman who contracted the virus due to accidental exposure to an imported case, was identified as the first confirmed local case in the outbreak on May 21.

Three cases were infected by her through close family contacts or dining.

Among them, the close family contact progressed to critical illness after admission to hospital.

Another patient, who progressed to severe illness, was the key transmitter in the third generation and infected five generations in the cluster.

The third case, a restaurant server with a short period of exposure to the elderly woman, was confirmed outside Guangzhou later.

Compared with a cohort of 260 people infected with the wild-type strain in Guangzhou early last year in the first wave of the pandemic, the Delta variant has a shorter incubation period of four days as opposed to six, a higher viral load and a longer duration of viral shedding in pharyngeal swab samples, the report said.

In some cases, the time from acquisition of infection to further spreading spanned just a single day, it added.

In cases of critical illness, the proportion of patients over the age of 60 was higher in the Delta group.

The Delta variant has a higher risk of deterioration to critical status, the research indicates.

According to epidemiological tracing and citywide viral nucleic acid screening in the outbreak between May 21 and June 18, the infections were identified as a cluster having a clear chain of transmission and sharing the same nucleic acid sequence as the Delta variant.

That represented a unique opportunity for a better understanding of the transmission and clinical characteristics of the Delta variant.

The research "is helpful for achieving effective containment of this emerging widespread variant", the report said.

The Delta variant was initially detected in India in October and has spread to at least 98 countries.