Recovered Covid-19 patients in China may still be vulnerable to a mutant form of the pathogen spreading overseas, a new study says.
According to Professor Huang Ailong from Chongqing Medical University, there is an urgent need to determine what threat the mutation, known as D614G, poses to people who have recovered from a different form of the virus.
D614G began spreading in Europe in early February and by May was the dominant strain around the world, presenting in 70 per cent of sequenced samples in Europe and North America.
Antibodies found in patients who had been infected with earlier forms of the pathogen failed to neutralise the mutant strain, the scientists said in paper published on Biorxiv.org, a preprint website, which means it has not been peer-reviewed.
Since the latest coronavirus outbreak was reported at the Xinfadi wholesale food market in Beijing, 227 new infections have been confirmed and more than 2.3 million residents have been tested for Covid-19 in a bid to contain the spread.
Health authorities identified the infection in a number of locations at the market, including inside the mouths of imported salmon. The whole genome sequencing data of samples from the first three patients have been released and they all contained the D614G mutation.
Huang and his team selected a strain of the virus that had previously circulated in China and then manipulated it to create a man-made version containing the mutation.
They then extracted antibodies from 41 blood samples collected from recovered patients and pitched them against the mutant.
According to a report published last week by Scripps Research, a medical research facility in San Diego, the D614G mutation has the potential to increase the number of spike proteins on the coronavirus and boost its ability to infect human cells by a factor of 10.
However, that estimate was mostly based on computer modelling so questions remained over the possible increase in binding efficiency.
In the Chongqing study, the antibodies generated by three patients failed to suppress the mutated strain, with one sample showing almost zero effect.
The researchers then tried to infect host cells with the mutant and normal strains. The mutant’s entry efficiency was 2.4 times higher.
“This seemingly small increase in entry activity could cause a large difference in viral infectivity in the human body,” they said.
One of the concerns now is that the prevalence of D614G will have a detrimental impact on vaccine development.
Several Chinese vaccine candidates have entered the final phase of clinical trials, but they are based – like those under development in the United States and Europe – on the earliest strains of the coronavirus detected and sequenced in Wuhan.
A study by IBM’s AI medical team in April warned that the D614G mutation could reduce the effectiveness of vaccine programmes that target the virus’ spike protein. A separate study by a team of researchers in Serbia last month came to a similar conclusion.
“Given the evolving nature of the SARS-CoV-2 RNA genome, antibody treatment and vaccine design might require further consideration to accommodate the D614G and other mutations that may affect the immunogenicity of the virus,” Huang said.
About 10 per cent of the people infected by the new outbreak in Beijing are in a critical condition, according to the city’s health authorities, and medical teams from across the country have been flown into to help with the aid effort.
The Chinese government and the World Health Organisation have both said the genetic information of the virus points to a source outside China, but whether it arrived via a refrigerated food chain or a human visitor has yet to be determined.
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