In Houston, TX, a specific mutation became almost ubiquitous in SARS-CoV-2 infections between March and July 2020. This strongly suggests that it makes the virus more infectious. There is no evidence, however, to indicate that it makes the virus any more deadly.
On March 5, 2020, Metropolitan Houston confirmed the first case of COVID-19, the disease that evolves as a consequence of SARS-CoV-2. The virus was circulating within the community a week later.
A previous study found that in the early phase of this first wave of infections, strains of the virus carrying a specific mutation, called G614, caused 71 percent of cases in Houston.
A follow-up analysis by the same team now shows that this variant accounted for 99.9 percent of all COVID-19 infections in the region by summer, during the second wave.
The new study that was led by a team from the Houston Methodist Hospital in Texas is now published in the mBio journal.
The mutation that has spread around the world results in the substitution of one amino acid for another at a specific location in the spike protein of the virus.
The building blocks of proteins are amino acids. They are assembled according to the genetic blueprint of the virus in a fixed series.
In the spikes, the mutation substituted an amino acid called aspartate with another called glycine, which allows the virus to break into its host cells. It seems that the replacement makes it easier for the virus to enter the cells.
A research earlier this year showed that in cell cultures that develop in the laboratory, viruses carrying this mutation are more infectious.
The same team found clinical evidence to indicate that in their upper respiratory tracts, individuals with this variant had more virus particles than individuals with other variants. Having said that, their illness seemed to be no more serious despite this extra “viral load.”
Another analysis in the U.K. of over 25,000 viral sequences It means that viruses with this mutation have transmitted slightly faster and have caused larger infection clusters.
The new research sequenced the genomes of the two COVID-19 waves in Houston from 5,085 strains of the virus.
People with the G614 variant had substantially more virus particles in their noses and throats at the time of diagnosis, likely due to its increased infectivity. However, there was no evidence to indicate that, as a result, these persons suffered more serious illness.
The researchers found 285 other mutations that cause changes in the amino acid sequence of the spike protein, in addition to G614.
In collaboration with scientists at the University of Texas at Austin and the University of Chicago, IL, researchers at Houston Methodist Hospital found that one of these mutations could enable the spike to evade a neutralizing human immune system antibody.
Whether or not this mutation often improves infectivity is unknown. The researchers, however, report that it is currently unusual and does not seem to make the disease more serious.
They also found no evidence to indicate that the virus has developed mutations that could make ineffective either the vaccines in progress or established antibody therapies.
However, study co-author Ilya J. Finkelstein, a University of Texas molecular biologist, urges continued caution.
“As it rips through the world, the virus begins to mutate,” he says. “Real-time monitoring activities like our study will ensure that one step ahead is still global vaccines and therapeutics.”
The genetic study of the team showed that several times, and from all corners of the world, the virus made its way to Houston. The researchers actually identified strains in the United States from Asia, Europe , South America, and elsewhere.
Concluding their report, the authors write:
“The findings will help us to understand the origin, composition, and trajectory of future infection waves and the potential effect of the host immune response and therapeutic maneuvers on SARS-CoV-2 evolution.”
They also note some of the study’s limitations. Their sample, for instance, may not have represented the full socioeconomic diversity of the population of the Houston metropolitan area.
They also write that only about 10 percent of all COVID-19 cases reported in the area during the study period were reflected by their samples.