A MUTANT strain of the coronavirus now accounts for the majority of global cases and could be more contagious than the original, researchers have said.
A survey of over 5,000 positive cases at a hospital in Houston, Texas found that 99.9 percent were caused by the new strain, known as D614G.
The variation first appeared in Europe in February, and now accounts for an estimated 85 percent of all cases globally.
The latest study, published in the mBio journal, will add to concerns that D614G is more contagious than the version – now known as the "D strain" – that first emerged in the Chinese city of Wuhan late last year.
Scientists are still working to establish how and why D614G became the dominant form of the virus.
One theory posits that it leads to greater levels of virus matter in the upper respiratory tract, meaning more is ejected when a person coughs, sneezes, or speaks.
After emerging in Europe, the strain is believed to have spread via air travel to Asia, the US, and elsewhere.
It is known to have spread to every continent by the end of February and to have accounted for over 50 percent of new cases globally by sometime in March.
It continued to spread, causing more than 70 percent of new cases in May and around 85 percent at present.
As in Houston, practically all cases in some localised outbreaks are caused by D614G.
A study at a New York hospital in September similarly found that 99 percent of cases were of the newer strain.
The Houston study found that the current prevalence of D614G had increased from 71 percent of new cases during the first wave of the pandemic in March.
"The virus continues to mutate as it rips through the world," said co-author Dr Ilya Finkelstein of the University of Texas at Austin.
“[It] is mutating due to a combination of neutral drift – which just means random genetic changes that don't help or hurt the virus – and pressure from our immune systems.
"Real-time surveillance efforts like our study will ensure that global vaccines and therapeutics are always one step ahead."
Researchers have reportedly identified 285 variations of the coronavirus so far, although most do not appear to noticeably change the severity of the disease.
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