The latest study by researchers from the Indian Sars-Cov-2 Genomics Consortium (Insacog) institutes, has assessed that variant B.1.617.2, named Delta, had 50% higher transmission rate and viral load than Alpha (B.1.117), besides a clearly higher ability to ‘breakthrough’ vaccine protection, though not linked to higher fatalities.
The study is in line with latest assessments on Delta, especially on people contracting infection despite vaccination. The latest study by the All India Institute of Medical Sciences and CSIR’s Institute of Genomics and Integrative Biology found 63 cases of breakthrough infections in fully vaccinated persons, and those with single dose of Covishield or Covaxin, and traced it to Delta.
A study by UK researchers published in the Lancet said while a single dose may give more protection than no vaccination, such recipients were likely to be less protected against Delta and Beta (B.1.351). It suggests speeding up the second dose against the fast spread of Delta.
The National Centre for Disease Control assessment on post vaccination infections shared in the Delhi outbreak study said that Delta was over-represented and Alpha not even detected in vaccination breakthroughs, suggesting higher breakthrough risk of Delta compared to Alpha.
Of the 27 vaccine breakthrough cases studied by NCDC, 76% to Delta and 8% to its sub type. The study could not find a clear link to higher deaths with Delta and said deaths were probably due to multiple factors, including “short-term collapse of the healthcare system.”
Delta showed “high transmissibility and surges without any increase in case fatality rate. We estimate the transmissibility to be as much as 50% greater” than Alpha. Delta’s viral load appeared to be higher than Alpha’s and based on data from India and UK, so did vaccination break-through rate, the study said. While immune escape seemed less for Delta compared to Beta or Gamma overall, the Union government supported study found Delta was “capable of creating very fast rising outbreaks with vaccination breakthroughs.”
“Since CFR may be due to an amalgamation of multiple factors, including the short-term collapse of the healthcare system, there is currently no clear evidence linking Delta to change in CFR. This will be reexamined once final information is available on all deaths and Covid-19-related deaths over this period,” the study’s pre-print version said.
Tracing the onset of the second wave in India with outbreaks in Kerala, Maharashtra and Punjab, the study said that Alpha outbreak in Punjab was marked by clusters spanning multiple districts, suggesting a mass super spreader event. It pointed to public gatherings and rallies held in different parts of north India since January and highlighted the important role of social factors in Covid-19 outbreaks.