Pre-lockdown exodus from Dhaka in 2020 spread COVID-19 across Bangladesh: study

The exodus from Dhaka after the announcement of the first lockdown in 2020 spread the coronavirus throughout Bangladesh, researchers have found.

The government’s disease control agency IEDCR conducted the study jointly with the International Centre for Diarrhoeal Disease Research, Bangladesh or icddr,b and some other government and private agencies.

In a statement on Tuesday, icddr,b said they found COVID-19 infection in Bangladesh in mid-February 2020, nearly a month before the first cases were reported in March.  

The researchers, however, did not reveal details about this finding.

They made the finds through the analysis of genome from 391 samples collected between March and July last year.

The IEDCR confirmed the first COVID-19 cases in Bangladesh on Mar 8. The first death from the disease was reported after another 10 days.

Until Tuesday, the government confirmed more than 1.53 million coronavirus cases while the death toll crossed 27,000.

It announced the first lockdown in the form of a 10-day general holiday from Mar 26 last year, shutting down offices, courts and public transports.

After the announcement, people left Dhaka and other cities for their home villages or towns. With the spread of the coronavirus, the lockdown was extended several times until June.

The icddr,b said they analysed the gene data with the information from the government’s a2i programme, Facebook and mobile phone operators on the exodus from Dhaka between Mar 23 and mar 26.

Researchers from the UK-based Sanger Genomic Institute, the Institute for Developing Science and Health Initiatives, the Harvard School of Public Health, and the University of Bath also worked in the study.

They published an analytical research paper in the Nature journal on how genomics, social media and mobile phone data for the mapping of SARS-CoV-2 lineages were used to inform health policy in Bangladesh.

Genomics, combined with population mobility data, used to map importation and spatial spread of SARS-CoV-2 in high-income countries has enabled the implementation of local control measures.

Here, to track the spread of SARS-CoV-2 lineages in Bangladesh at the national level, the researchers analysed outbreak trajectory and variant emergence using genomics, Facebook ‘Data for Good’ and data from three mobile phone operators.

They sequenced the complete genomes of 67 SARS-CoV-2 samples, collected by the IEDCR in Bangladesh between March and July 2020, and combined these data with 324 publicly available Global Initiative on Sharing All Influenza Data SARS-CoV-2 genomes from Bangladesh at that time.

Bayesian time-scaled phylogenetic analysis predicted that SARS-CoV-2 first emerged during mid-February in Bangladesh, from abroad, according to the Nature publication.

The shifting pattern of viral diversity in Bangladesh, combined with the mobility data, revealed that the mass migration of people from cities to rural areas at the end of March, followed by frequent travel between Dhaka and the rest of the country, disseminated three dominant viral lineages.

Further analysis of an additional 85 genomes from November 2020 to April 2021 found that importation of Beta variant of the coronavirus had occurred and that Beta had become dominant in Dhaka.

The researchers’ interpretation that population mobility out of Dhaka, and travel from urban hotspots to rural areas, disseminated lineages in Bangladesh in the first wave continues to inform government policies to control national case numbers by limiting within-country travel.