Study: Delta variant more transmissible than the others | Latest India News
The number of secondary infections caused by a person infected with the Delta variant (B.1.617.2) of Sars-Cov-2 increases by 97% compared to the virus first seen in Wuhan, according to a study in the United Kingdom. He concluded that this variant first seen in India is much more transmissible than any other variant.
The study, published in the European journal of infectious diseases, Eurosurveillance, assessed data uploaded by 64 countries into the Sars-CoV-2 global genome sequencing database GISAID. He found that the effective number of breeding increased by 29% for the Alpha variant (B.1.1.7) first reported in the UK, by 25% for the Beta variant (B.1.351) reported in Africa. South and 38% for the Gamma variant. (P.1) variant reported for the first time in Brazil.
Of the six variants of interest, the researchers found two to show statistically significant increases in effective reproductive number – the Kappa variant (B.1.617.1) by 48% and the Eta variant (B.1.525) by 29%. .
But what does a 97% increase mean? “This means that if the previous virus was transmitted from person to person, the Delta variant would spread to four people,” said Dr T Jacob John, former head of the virology department at Christian Medical College-Vellore.
He added that the effective reproductive number is based on two factors – the R0 (R-nought) or a fixed reproductive number for each virus, and the immunity of the population. “I’m not sure how they calculated the effective reproduction number regardless of population immunity, but what they showed is a collective upward trend in variants across 64 countries,” John said. .
The researchers found a “clear competitive advantage” of the Delta variant over the Alpha, Beta and Gamma variants. The effective reproduction number of the Delta variant has increased by 55% over Alpha, 60% over Beta, and 34% over the Gamma variant.
This was consistent with the finding of a 42% increase in the secondary attack rate (the likelihood of an infection occurring in a specified unit, such as the household or among close contacts) of the Delta variant according to surveys. epidemiological studies in the United Kingdom.
Indian doctors have also repeatedly pointed out that the secondary attack rate was much higher during the second wave of the pandemic in April-May, when almost everyone in a household contracted the infection if a person was infected – something that hadn’t happened before. .
The researchers said that to control the pandemic, given the rapid spread of the Delta variant in many countries, tighter restrictions will need to be imposed and for longer periods. The spread will also expand healthcare systems, as seen in India at the height of the second wave, where people struggled to find beds in hospitals.
Dr Anurag Agarwal, director of the Institute of Genomics and Integrative Biology, said the study is consistent with “what has already happened”. “A huge and fast second wave. This is the same as what we said in our pre-print study: that the Delta variant is up to 50% more [transmissible] than the Alpha variant, and the Alpha variant is more [transmissible] than non-variants, ”he said.
The number of infections is much lower in India right now, but the Center has called on states and Union Territories not to let their guard down.
British researchers said that higher transmissibility also means that the herd immunity threshold will increase, leading to increased vaccine coverage targets.
Dr John said the immunity of the people in India was already very high after the huge second wave of infections in April-May. “I estimate that the immunity at the population level is already 80% in India. Immunization must now target people with co-morbidities and pregnant women to avoid deaths. Childhood immunizations must also be introduced so that schools can reopen safely, ”he said.
However, the researchers left a warning note. “The convergent evolution of mutations thought to be associated with higher transmissibility or immune evasion highlights the fact that variants are likely to continue to emerge under selective pressures. The emergence of new variants threatens the efficacy of vaccines and requires constant evaluation of diagnostic, therapeutic and vaccine strategies available as the Covid-19 pandemic continues, ”the study concludes.