International study reveals how Delta came to dominate the pandemic
A comprehensive new study, published in the journal Nature, is describing how the Delta variant of SARS-CoV-2 has so rapidly become dominant all over the world. The research offers thorough evidence Delta’s effective spread is through a combination of greater resistance to immune antibodies and a more efficient ability to infect cells and replicate compared to prior virus variants.
First recorded in India in December, 2020, the Delta variant of SARS-CoV-2 has spread across the globe at an incredible rate. Clearly outperforming all other currently circulating variants, Delta is now the dominant form of SARS-CoV-2 and present in most countries around the world.
This new study is the result of a massive international collaborative effect involving dozens of scientists. The first arm of the research investigated how effectively the Delta variant evades pre-existing immune antibodies generated either by a prior COVID-19 infection or a vaccination.
Across a series of in vitro experiments the researchers found the Delta variant was six times less sensitive to immune antibodies from individuals who had recovered from a prior COVID-19 infection, and eight times less sensitive to vaccine-induced antibodies. This sensitivity was compared to antibody responses generated against the original strain of SARS-CoV-2.
The second arm of the study focused on how the Delta variant more efficiently infects and replicates within host cells. Here the researchers generated a cellular model of an airway grown from human cells.
Observing the virus infecting these cells in detail revealed the Delta variant’s increased ability to break into cells compared to other SARS-CoV-2 variants. The researchers suggest this ability is mediated by a greater volume of what are known as cleaved spikes.
A synthetic version of Delta, known as a pseudotyped virus, was created to mimic a few key mutations. This effectively confirmed the increased number of cleaved spikes on the virus surface is what helps Delta more efficiently enter host cells.
Once inside those cells the Delta variant was also found to replicate faster than previous variants. These factors, the researchers hypothesize, are why Delta has so quickly become dominant over all other variants currently circulating.
“By combining lab-based experiments and epidemiology of vaccine breakthrough infections, we’ve shown that the Delta variant is better at replicating and spreading than other commonly observed variants,” says Ravi Gupta, a senior author on the new study from the University of Cambridge. “There’s also evidence that neutralizing antibodies produced as a result of previous infection or vaccination are less effective at stopping this variant. 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 says we may need to begin considering Delta-specific vaccines, as the study also analyzed around 100 vaccinated healthcare workers who were subsequently infected with the Delta variant. Current vaccines were still found to be profoundly effective at preventing severe disease, hospitalization and death, however, the research found vaccinated individuals infected with Delta were transmitting the virus to others at greater levels than previous variants.
Anurag Agrawal, from India’s CSIR Institute of Genomics and Integrative Biology and joint senior author on the new study, says this kind of breakthrough viral transmission is a significant problem as it allows the virus to silently spread through vaccinated communities until it catches either vulnerable populations or the unvaccinated.
“Infection of vaccinated healthcare workers with the Delta variant is a significant problem,” says Agrawal. “Although they themselves may only experience mild COVID, they risk infecting individuals who have suboptimal immune responses to vaccination due to underlying health conditions – and these patients could then be at risk of severe disease. 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.”
The new study was published in the journal Nature.
Source: University of Cambridge