Virus may be more contagious than before

Research shows main strain circulating here has higher chance of infection than original

Evidence is growing that a mutated novel coronavirus strain, the main one circulating in the Houston area, is more contagious than the original virus in China.

Two new research papers show that the newer strain is more transmissible, a possibility first suggested by a team of scientists in May. At the time, that suggestion was considered highly speculative by many scientists, including some in Houston.

“A summary of the data thus far suggests that this strain has gained a fitness advantage over the original and is more transmissible as a result,” said Joseph Petrosino, Baylor College of Medicine chair of molecular virology and microbiology. “It is safe to say this version is more infectious.”

Petrosino said that although Baylor hasn’t yet conducted a surveillance study, the area rate of positive tests and increase in hospitalizations point to a significantly higher prevalence of the virus strain now. He said Baylor is finding the mutated strain in as many as 80 percent of viruses it analyzes.

Houston Methodist researchers reported the strain was prevalent in the Houston area in a paper in mid-May. The paper said 70 percent of the specimens examined, taken from COVID-19 patients treated at Methodist from early March to March 30, showed a mutation to the spike proteins the coronavirus uses to attach to and enter human respiratory cells.

The week before, researchers at Los Alamos National Laboratory reported on the mutation. They said it doesn’t make people sicker but appears to facilitate the spread of the virus.

The Los Alamos team expanded on the findings in a peer-reviewed paper published in the journal Cell last Thursday.

The Methodist researchers were among scientists skeptical of that conclusion. Dr. James Musser, the hospital’s chairman of pathology and genomic medicine and a study author, said Friday he would like the science to play out a bit more as studies reviewed by scientists are published. He gave no update on the percentage of mutated strains analyzed at Methodist.

The mutation is thought to have occurred in Europe, then was introduced by travelers to the East Coast of the U.S., particularly New York. It has since become the world’s most dominant strain, accounting for about 65 percent of cases submitted to a major database from around the world, according to one team of scientists.

Except for the new Cell publication, all of the papers are examples of what is known as “pre-prints,” preliminary reports made public ahead of their peer-reviewed publication because of the discoveries’ time-sensitive nature.

One of the papers, by a Scripps Research Institute team, showed that significantly increasing the number of functional spikes on the viral surface in laboratory experiments allowed the virus to bind to and infect cells. It said that the mutation provides greater flexibility to the spike’s “backbone,” which makes viral particles better able to navigate the process fully intact.

“Over time, it has figured out how to hold on better and not fall apart until it needs to,” Michael Farzan, a paper author and cochairman of the Scripps department of immunology and microbiology, said in a news release.

Another paper, by the New York Genome Center, found a huge increase in viral transmission when researchers switched from the original virus sequence to the mutated one, a change they interpret as an indication the new strain is more efficient at invading the human cell and taking over its reproductive machinery.

At least three other lab experiments suggest that the mutation makes the virus more infectious, the Washington Post reported Thursday. Those findings also appeared in pre-prints.

The mutation, known as D614G, involves one of roughly 1,300 amino acids that act as building blocks for the spike protein. Not much different from the original virus, it switched genetic instructions for the amino acid 614 from an aspartic acid (D) to a glycine (G).

In the Cell paper, the Los Alamos researchers wrote that patients with the D614G mutation have more virus in their bodies. Their laboratory experiments found the mutation is three to six times more capable of infecting human cells.

Strains of the virus circulating in the Houston area also include the original one from China and one from South America, according to Methodist’s study. The area’s multiple-continent seeding contrasts with relatively single-continent seeding in New York and Seattle. Seattle’s came mostly from Asia.

Many scientists, noting one paper found no evidence of increased transmissibility, say the evidence for D614G’s greater contagiousness is still far from definitive. “This is an extraordinarily challenging problem, the evolution and demography are complex, so there’s much more work to be done,” Marc Suchard, a biostatistician at the UCLA School of Medicine, told the New York Times.

Though Baylor’s Petrosino suggests the mutated strain is more prevalent, he adds that the recent spike is mostly a result of people’s wanting to gather and being willing to take risks to do so.

“The bulk of it is from people not social distancing properly, not masking appropriately and a reluctance to participate in contact tracing,” Petrosino said. “People have been getting tired of the safety measures and have started becoming more lax in their practices.”