Qunli branch of the First Hospital of Harbin Medical University Photo: Xinhua

The coronavirus genome sequence of the infection chain occurring in Harbin, Northeast China's Heilongjiang Province, is obviously different from that of viruses previously found in Chinese COVID-19 patients, an official study showed, which virologists said it proves that coronavirus has multiple origins.

Two batches of samples taken from 21 patients in Harbin's clustered infection showed that 99.99 percent of their genome sequences were consistent. Moreover, genome sequences of 18 among the 21 were fully identical, while that of the other three only show 1-2 nucleotides difference, according to Zhang Xue, head of Harbin Medical University and also the head of Heilongjiang Academy of Medical Sciences.

"Through gene sequencing analysis, it is obvious that the genome sequence of the coronavirus in this transmission chain is significantly different from that of viruses previously spread in the Chinese population," Zhang revealed at a press conference on Tuesday.

The genome sequences of the virus found in the 21 people and a recent epidemiological investigation further confirmed the virus infections in Harbin were sourced from one single infection chain, which was from overseas, meaning the virus was spreading from a person returning from the US, Zhang said.

"The genome sequences study manifested that the coronavirus very likely has multiple origins and their transmission capabilities are different," Yang Zhanqiu, deputy director of the pathogen biology department at Wuhan University, told the Global Times on Tuesday.

The worldwide genotypes of the coronavirus vary in different regions, which implies there is more than one source of virus origin in the world. The virus may turn into different genotypes in order to better fit with immunity systems of locals, Yang said.

The study further shows that asserting that Wuhan is the origin of the virus is baseless, Yang said, slamming forces who try to blame China and make China a scapegoat for the pandemic for political purposes.

"No scientific evidence has shown that Wuhan is the origin of the coronavirus. The city was only the region that reported the first COVID-19 cases in the pandemic. The coronavirus could have originated in the US given some people who died from influenza last year actually died from coronavirus infection," Yang noted.

The number of confirmed COVID-19 cases in the US approached 1 million as of Tuesday, which is a rapid rate of increase when the first case in the US was reported in January, proving that strains of the virus sourced in the US have stronger virulence and stronger transmission, Yang noted.

Two batches of genome sequences were taken from the infection chain in Harbin and were sent to the Chinese Center for Disease Control and Prevention on April 15 and an epidemiological investigation was also conducted in Harbin.

A Chinese national surnamed Han who returned from the US, started the chain of infection by passing the virus on to her neighbor despite Han taking four nucleic acid tests and antibody tests that came back negative. The neighbor's family then held a gathering and one of the attendees went to a hospital after suffering a stroke, leading to clustered infections at two hospitals.

Han, as the source of the infection chain, had contacted 87 people in total, as of Monday. In the infection chain, 62 are Harbin locals, three are from other provinces including North China's Inner Mongolia Autonomous Region and Northeast China's Liaoning Province, plus 22 asymptomatic infections, official data shows.

"When Han finished home quarantine in Harbin, the relevant departments conducted several nucleic acid tests on her, and they were all negative. But the two IgG antibody tests were positive, proving that she had virus antibodies," Zhang said.

Zhang said this shows that the coronavirus in Han's body has been defeated by her own immune system and the chance of infecting others is greatly reduced, meaning the possibility of transmission of the virus by Han to others is reduced.