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Delta grew to become the dominant variant in India due to its improved ability to jump to new hosts and by wiping resisting the large parts of population immunity in people from the first wave of Covid-19, a new study awaiting peer view has suggested, reporting finding that show the unique set of mutations makes the virus more infective, leads to higher viral load in people and causes larger outbreak clusters.
The findings are by researchers in India and India, and takes into account outbreak patterns among healthcare workers in three Indian cities, and lab analysis of how the variant reacts to antibodies as well as the way in which the virus infects human cells, particularly in the lungs.
The study made several crucial findings, some of which, to be sure, have also been reflected in real world data coming from the UK. The researchers included scientists from Institute of Genomics and Integrative Biology (IGIB) in collaboration with Cambridge University’s Gupta Lab.
“The main finding of the paper is that the Delta variant has a good immune escape potential as shown in the lab. It also quickly replaced other variants and caused most of the breakthrough infections (infection after complete vaccination) in healthcare workers. For the people, what this means is that we have to be very cautious and behave appropriately, especially now that we are also seeing cases of Delta Plus. We still do not know anything about its immune escape potential. The studies have just started,” said Dr Rajesh Pandey, one of the authors of the paper and senior scientist at the Institute of Genomics and Integrative Biology.
“Delta variant has the maximum transmissibility yet seen, and reduces neutralisation protection from previous infections and vaccines,” said Dr Anurag Agarwal, one of the authors of the study and the director of the Institute of Genomics and Integrative Biology.
The mathematical model based on cases and deaths reported from Mumbai showed that by the end of January, there was a 2% increase in the transmissibility of the Delta variant against all others in circulation, and a 32% increase in immune evasion from a previous infection (if the researchers assumed that there was 30% under-reporting of deaths). The proportions go up if the assumption is 50% and 70% under-reporting of Covid-19 deaths.
“We find that Delta is both more transmissible and better able to evade prior immunity elicited by previous infection compared to previously circulating lineages. While there is substantial uncertainty in our estimates, we find that in Mumbai, the Delta variant was 10% to 40% more transmissible than previously circulating lineages, and able to evade 20 to 55% of the immune protection provided by prior infection with non-Delta virus,” said a tweet from the collaborating Gupta Lab from Cambridge University.
The in-vitro, or laboratory studies, looked at sensitivity of the variants of concern to neutralising antibodies from a previous infection by the virus that originated in Wuhan. It showed that Alpha variant, seen first in the UK, was 2.3 fold less sensitive and, Beta — seen first in South Africa — was 8.2 fold less sensitive as compared to 5.7 fold for Delta variant.
The researchers also found that Delta variant had a replication advantage over Alpha variant in the lab. The researchers also found that when samples of over 100 healthcare workers from three Delhi hospitals who got breakthrough infections were sequenced, most of them were caused by the Delta variant.
“However, by the time a significant proportion of the healthcare workers were fully vaccinated, Delta variant was the most common variant in circulation, accounting for 60% of cases. So, that could also be the reason why most breakthrough infections were caused by delta variant,” said Dr Pandey.