More contagious strain virtually the only one circulating inhouston

A mutated, more contagious coronavirus that Houston scientists reported was the primary strain circulating in the area in the pandemic’s early days is now virtually the only one infecting people here, according to the team.

In a new study released Wednesday, Houston Methodist scientists reported that more than 99 percent of samples of the virus they’ve sequenced since midMay contained the mutation that allows it to infect more people, up fromabout 70 percent the previous two months.

“We’ve now done molecular analyses of the two waves of the pandemic and one thing that stands out is the increase in the mutated strain’s frequency over a short period of time,” said Dr. James Musser, Methodist’s chairman of pathology and genomic medicine and the study’s author. “Clearly, this strain is very different.”

But Musser emphasized there is “no evidence the strain is any more virulent,” meaning it is no more likely to cause death or extended hospitalization. But it does seem to facilitate the virus’ spike proteins ability to attach to enter human respiratory cells.

The strain’s increased dominance beginning in mid-may likely “contributed” to the dramatic spike in COVID-19 cases after Memorial Day, Musser acknowledged. But he noted the virus could have been controlled reasonably well with the known measures — masks, proper social distancing, and the avoidance of large gatherings.

The study has not yet been peer-reviewed. It was posted on the preprint server Medrxiv, which hosts preliminary reports made public ahead of peer-reviewed publication because of the urgent nature of the pandemic.

Themutation is likely similarly dominant around the country, said Musser. But the study only looked at samples collected in Houston.

Methodist scientists have been sequencing the coronavirus’ genome since it arrived in early March. The study looked at more than 5,000 samples of the virus, the most sequenced so far.

The team reported on their first findings in May. That study found the virus that causes COVID-19 was introduced in the Houston area beginning in early March from a multitude of geographic regions, including Asia, Europe and South America. It found most of the strains were the mutated ones from Europe, not the original one that originated in Asia in December 2019.

Researchers at Los Alamos National Laboratory in New Mexico had previously speculated that the mutation made the virus more contagious, an idea not initially embraced by many scientists, includingmusser. He said he still wanted more evidence when the first such evidence was reported a couple of months later.

But Musser said Wednesday the “preponderance of evidence” now suggests the mutated strain is more contagious. That includes his study, which found there is a higher viral load associated with the strain.

Musser said the high viral load engenders easier transmissability rather than virulence because it is in the upper respiratory system, not the bloodstream.

The study found the pandemic’s two Houston waves — March to early May, then mid-may through August — first infected older, more affluent individuals, then younger, lower-income neighborhoods.

Musser said the design of the vaccines in clinical trials and under development cover the mutated virus. But he said the mutation raises the concern that once people have widespread immunity to the virus, it could develop mutations that enable it to escape. If that were to become the case, he said, it might be necessary to develop new vaccines annually, as is done for the flu.

Mutations occur randomly as the virus makes copies of its genomewithin humancells. But the more cases there are — the virus’ spread has provided ample such opportunities — the greater the odds the mutation will have consequences.

“A lot of this is a numbers game,” saidmusser. “Roll the dice enough and you get a large number of mutations.”

Scientists from the University of Texas at Austin, Weill Cornell Medicine and the University of Chicago, Argonne National Laboratory also contributed to the study.