The country has started developing herd immunity against Covid-19 as indicated by a new study on seroprevalence among the Dhaka city dwellers, including the inhabitants of slums.
About 45 per cent residents and 74 per cent of slums dwellers in Dhaka city have been infected with coronavirus by July, the study has revealed.
The exposure to Covid has occurred in the study areas, senior scientist at ICDDR,B Dr Firdausi Qadri told the dissemination ceremony of the study findings.
"The encouraging rate of seropositivity among the study population of Dhaka city indicates that the country has started developing herd immunity against Covid-19," he told the virtual meeting.
The Institute of Epidemiology, Disease Control and Research (IEDCR) in collaboration with USAID organised the programme on 'Prevalenece, Seroprevalence and Genomic Epidemiology of COVID-19 in Dhaka' at a city hotel on Monday.
Bill and Melinda Gates Foundation provided the financial assistance for the study.
Health minister Zahid Maleque joined the programme virtually as the chief guest. Additional director general of DGHS Professor Dr Meerjady Sabrina Flora chaired the programme.
Seroprevalence is the number of persons in a population who test positive for a specific disease based on serology (blood serum) specimens; often presented as a per cent of the total specimens tested or as a proportion per 100,000 persons tested.
As positively identifying the occurrence of disease is usually based upon the presence of antibodies for that disease (especially with viral infections such as herpes simplex, HIV, and SARS-CoV-2), this number is not significant if the specificity of the antibody is low.
Between April 18 and July 5 last, the prevalence of covid-19 was 9.8 per cent on the day of collecting samples. This implies that one in ten individuals were tested Covid positive in Dhaka city.
The study also found 45 per cent people, who were asymptomatic, finally diagnosed as corona positive. The age of the population who have developed antibody is between 24 to 60 years.
The Covid prevalence was highest 24 per cent among the elderly, aged over 60, followed by 18 per cent among adolescents, aged 15-19 years. Among the positive cases, 82 per cent were asymptomatic, 6.0 per cent symptomatic and 12 per cent pre-symptomatic.
It was found by genome sequencing that the first corona infection occurred in Bangladesh in mid-February.
The study team randomly selected 25 wards of Dhaka North and South city corporation out of the total 129.
They selected one mahalla from each ward and 120 households from each mahalla. Besides they selected eight slums additionally.
The samples of general residents of Dhaka city were collected between mid-April and mid-July. The samples of the slum dwellers were collected between mid-July till mid-August.
The study also said that the virus spread mainly in March last correlating with the mass migration evidenced by the mobility data.
Lineages circulating in Bangladesh are closely related to those circulating globally, suggesting therapeutics and vaccine would be just as likely to be effective in Bangladesh as elsewhere in the world.