First surfacing from the state of Maharashtra in India during the latter part of 2020, the B.1.617.2 variant of the SARS-CoV-2 virus, perhaps better known as the Delta variant of the virus, the strain has since swept across the globe, starting from India and Europe, then finally the Americas and the rest of the world. As of August 10, the new dominant variant has been reported in at least 142 countries, with the list potentially at risk of growing given the variant’s transmissibility—the United States’ Centers for Disease Control and Prevention (CDC) reports that the Delta variant is more than twice as contagious as the variants that came before. Now, a team of researchers from around the world has shed some light on exactly how the notorious variant has cemented itself as the dominant strain around the world, beating out even the likes of the B.1.617.1 and B.1.1.7 variants, also known as the Kappa and Alpha variants of SARS-CoV-2. The study was published in the journal Nature.
Several in vitro studies, or studies done on cells or biological molecules outside their original biological context like internal bodies, were performed on the Delta variant while being compared to a baseline established by the original strain of SARS-CoV-2. This original strain is known as the wild-type (WT), which in this study bore the D614G mutation. (Institutions like the CDC recognize that the D614G mutation is at least partly responsible for the virality of the original virus.)
In the first arm of the study, the team found that, compared to the sensitivity of antibodies to WT, the Delta variant was six times (6×) less sensitive to antibodies from individuals who had already been infected with COVID-19, and eight times (8×) less to vaccine-induced antibodies.
In the second arm, the team devised a cellular model of an airway, grown from human cells. In it, the researchers hoped to understand how effective the Delta variant is at infecting, and replicating within, host cells. Observation of the impact of the Delta variant on these airway models revealed that it was the presence of a greater volume of “cleaved” spike proteins on the virus, compared to WT, that was responsible for its heightened ability to break into cells to begin viral replication.
The team mentioned that they confirmed this finding by creating a pseudotyped Delta variant virus, or a synthetic version of B.1.617.2, with the purpose of mimicking key mutations in the original Delta variant; this resulted in the pseudotyped Delta variant gaining a similar cell entry capability compared to the real version. The Delta variant was also found to be capable of faster replication within host cells compared to WT. All these factors, the team believes, are the reasons why the Delta variant has been so successful in infiltrating and infecting human populations, beating out even preexisting SARS-CoV-2 variants that came earlier.
The study also analyzed 100 cases of vaccinated healthcare workers who were still infected by the Delta variant. Here, they found that vaccination was still effective at preventing severe disease manifestation, hospitalization, and death; despite this, healthcare workers infected by the Delta variant were capable of greater amounts of viral transmission to other individuals compared to previous variants. Senior author Anurag Agrawal, from India’s CSIR Institute of Genomics and Integrative Biology, warns that this property of the Delta variant poses a significant problem, as it allows the virus to linger in vaccinated populations relatively undetected, posing a threat to vulnerable or otherwise unvaccinated communities.
Fellow senior author Ravi Gupta, from the University of Cambridge in the United Kingdom, believes that they’ve successfully shown the higher effectiveness of the Delta variant, compared to other variants, by “combining lab-based experiments and epidemiology of vaccine breakthrough infections, and that “these factors are likely to have contributed to the devastating epidemic wave in India during the first quarter of 2021, where as many as half of the cases were individuals who had previously been infected with an earlier variant.”
Gupta also believes that serious consideration needs to be given to developing vaccines specifically targeting the Delta variant of SARS-CoV-2. Agrawal added: “We urgently need to consider ways of boosting vaccine responses against variants among healthcare workers. It also suggests infection control measures will need to continue in the post-vaccine era.”
(To learn more about how the SARS-CoV-2 virus enters the cells in your body, feel free to check out our article about it here on modernsciences.org.)
Bibliography
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- Centers for Disease Control and Prevention. (2021, August 26). Delta Variant: What We Know About the Science. Centers for Disease Control and Prevention. Retrieved September 21, 2021, from https://www.cdc.gov/coronavirus/2019-ncov/variants/delta-variant.html
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