New research into the Covid-19 Delta wave in India offers valuable insights for handling future pandemics.

The University of Southampton's WorldPop research group has examined detailed data from 2020 and 2021, focusing on population movements, public events, and government interventions.

Their study, published five years after the global pandemic began, highlights the combination of factors that led to the rapid spread of the Delta variant, high daily case numbers, and significant mortality.

The research team used an advanced data analysis framework to identify transmission drivers and their delayed impacts, providing insights for future pandemic responses.

Dr Eimear Cleary, senior research fellow at WorldPop, said: "The first Covid-19 wave in India was relatively mild, but the second wave which began in March 2021 – during which the Delta variant emerged – was severe, with very high associated mortality."

In April 2021, India had the highest number of new and active Covid cases globally, and an estimated 2.7 million Covid-related deaths occurred between April and July 2021.

Dr Cleary added: "We looked at the movement of people on a population level, climate drivers associated with transmission – such as temperature, UV index and precipitation, timings and stringency of government restrictions, public events, and the lagged impact of drivers of transmission on Covid-19 incidence."

The Delta variant emerged alongside major public events, including the Kumbh Mela religious festival in April 2021.

Dr Cleary explained: "The increase in mobility, together with a relaxation of restrictions and the emergence of the Delta variant seem to have been the biggest contributory factors to the high levels of Covid-19 transmission observed during the second pandemic wave."

The WorldPop team found that people's movements returning to almost pre-pandemic levels was a main contributor to Covid-19 transmission during the Delta wave.

Dr Cleary said: "This research highlights the value of advanced data analysis frameworks incorporating lagged effects for estimating the impact of interventions on transmission, which will be extremely beneficial for managing future epidemics and outbreaks."

The research is published in the journal PLOS Global Public Health.

Throughout the pandemic, WorldPop has conducted extensive research to track and map the spread of Covid-19 globally.