The transition of the novel coronavirus from the D614 form to the G614 variant is not expected to negatively affect vaccine and treatment studies, according to a medical doctor.
Since originating in China last December, the COVID-19 pandemic has claimed nearly 580,000 lives in 188 countries and regions.
More than 13.35 million cases have been reported worldwide, while over 7.36 million people have recovered so far, according to figures compiled by the US’ Johns Hopkins University.
The virus has mutated, becoming more infectious.
According to a study — entitled Tracking changes in SARS-CoV-2 Spike: evidence that D614G increases infectivity of the COVID-19 virus — published in the journal Cell, the D614G mutation causes a small but effective change in the coronavirus spike protein which the virus uses to enter human cells.
The study was conducted by researchers from Los Alamos National Laboratory in New Mexico and Duke University in North Carolina in the US and the University of Sheffield in the UK.
According to the study, researchers developed a bioinformatic pipeline to identify Spike amino acid variants which are increasing in frequency across many geographic regions by monitoring data of GISAID initiative. By early April 2020, it was obvious that the Spike D614G mutation was exhibiting this behavior and the G614 variant has replaced the D614 variant as the dominant pandemic.
The study found that “the G614 variant is associated with greater infectivity and clinical evidence which is associated with higher viral loads, although not with increased disease severity.”
“We found that the G614 variant grows to higher titer as pseudotyped virions. In infected individuals, G614 is associated with lower RTPCR cycle thresholds, suggestive of higher upper respiratory tract viral loads, although not with increased disease severity. These findings illuminate changes important for a mechanistic understanding of the virus and support continuing surveillance of Spike mutations to aid in the development of immunological interventions,” it said.
The question arises as to whether that kind of change will impact the development of vaccines and treatments designed to fight COVID-19.
“D614G mutations and other possible mutations are possible as long as the virus is in circulation. However, the D614G mutation is not directly involved in RBD [the receptor-binding domain], so it is not expected to lead to a significant reduction in the immune response planned to be provided by vaccine studies to be developed,” said Riza Durmaz, a professor of Medicine Faculty at Yildirim Beyazit University in Ankara, Turkey who conducts research in molecular microbiology, bacteriology, virology, and immunology.
“However, as there may be mutations which cause seasonal antigenic changes, such as the influenza virus, it would be useful to monitor mutations in the genetic structure of SARS-CoV-2,” said Durmaz, referring to the virus which causes the COVID-19 disease.
Durmaz also said that despite the prevalence of the G614 mutation, coronavirus cases have begun to drop in many parts of the world since April, and no unexpected growth rate in cases has been recorded although coronavirus measures have been eased across the world.
“Therefore, it cannot be said that the G614 mutation has an effect on the normal rise in cases which occurs during the normalization and mitigation stages of coronavirus measures,” he added.
Herd immunity seems possible
Herd immunity has been one of the key topics discussed in fighting the coronavirus.
“When most of a population is immune to an infectious disease, this provides indirect protection — or herd immunity (also called herd protection) — to those who are not immune to the disease,” according to the Johns Hopkins Bloomberg School of Public Health.
“Depending how contagious an infection is, usually 70% to 90% of a population needs immunity to achieve herd immunity [through vaccination or previous infections],” it said.
However, a study published in The Lancet medical journal — titled The prevalence of the SARS-CoV-2 in Spain (ENE-COVID): a nationwide, population-based seroepidemiological study — created suspicion over the feasibility of herd immunity as a way to fight SARS-CoV-2.
“Despite the high impact of COVID-19 in Spain, prevalence estimates remain low and are clearly insufficient to provide herd immunity. This cannot be achieved without accepting the collateral damage of many deaths in the susceptible population and overburdening of health systems. In this situation, social distance measures and efforts to identify and isolate new cases and their contacts are imperative for future epidemic control,” the study said.
Nevertheless, Durmaz said that herd immunity is possible if 60%-70% of the society becomes infected.
“Herd immunity depends on the fact that as many people as possible in the society meet the virus and produce an antibody,” he added.
“The fact that antibody response is detected in more than 90% of individuals who have been confirmed by RT-PCR [reverse transcription polymerase chain reaction] when they encounter the virus supports that there will be no problem in terms of an immune response in this population against the virus,” Durmaz added.
Asymptomatic people pose threat in fighting COVID-19
In addition, the same study said that “a third of people with SARS-CoV-2 infection remain asymptomatic, which has important public health implications. Regional seroprevalence data offer valuable information to tailor public health policies against this epidemic.”
The Turkish professor underlined that asymptomatic people play an important role in the spread of the virus while symptomatic people are hospitalized and treated so the spread of the disease can be contained.
Durmaz said that people in a short phase of a couple of days before showing clinical symptoms or those who reproduce the virus in their bodies and spread without any symptoms come to play in occurrence of new cases.
“However, an important problem which arises here is that the available tests are insufficient to detect a significant part of asymptomatic patients.”
“The more economical and feasible way in the fight is that each individual accepts themselves as a potential asymptomatic and wears face masks and observes social distancing rules,” Durmaz added.
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