‘Delta variant counted for 60% of Delhi cases in April’
New Delhi, June 4: The rapid surge in cases during Delhi’s fourth Covid19 wave was mainly driven by the Delta variant— which likely has immuneevasion properties — and counted for 60 per cent of the cases in April, according to a new study.
The Delta variant, B.1.617.2, is 50 per cent more transmissible than the Alpha variant, B.1.1.7, first discovered in the UK, say researchers from the National Centre for Disease Control (NCDC) and the CSIR Institute of Genomics and Integrative Biology (IGIB).
Prior infections, high seropositivity, and partial vaccination are insufficient impediments to the spread of the Delta variant, found the scientists. They traced the factors contributing to the scale and speed of the fourth wave that started in April in Delhi and compared them to the preceding three waves last year.
“We find that this surge of SARS-CoV-2 infections in Delhi is best explained by the introduction of a new highly transmissible variant of concern (VOC), B.1.617.2, with likely immune-evasion properties,” the researchers noted.
The variant may have led to insufficient neutralising
immunity in people, despite high seropositivity, and social behaviour may have augmented the surge by promoting transmission, they added.
Neutralising immunity consists of naturally occurring antibodies that play an important role in the immune system.
To determine whether SARS-CoV-2 variants may be responsible for the April 2021 outbreak in Delhi, the researchers sequenced and analysed community samples from Delhi from the previous outbreak in November 2020 until May 2021 and related it to effective reproductive number, R(t).
The effective reproductive
number is the expected number of new infections caused by an infectious individual in a population where some individuals may no longer be susceptible.
The yet-to-be-published paper, posted on the preprint repository medRxiv, on Thursday, noted that the incidence of the Alpha variant was minimal in Delhi in January, rapidly increasing to 20 per cent in February and 40 per cent in March.
However, the rapidly spreading Alpha variant was overtaken in April by the Delta variant, first found in Maharashtra, the authors of the study noted.