Around 72% slum dwellers and 62% non-slum people in Dhaka and Chattogram were found to be carrying Covid-19 antibodies, says a study.
The study, carried out by the International Centre for Diarrhoeal Disease Research, Bangladesh (icddr,b), also found 71% slum dwellers in Dhaka and 55% slum dwellers in Chattogram to have developed coronavirus antibodies.
An individual having antibodies in the blood means he developed it after being infected or exposed to the virus, and his body produced antibodies in response.
The icddr,b conducted the study titled "Drivers of Covid 19 in Slums and Non-slum Areas of Dhaka and Chattogram" on 3,220 participants from slum and non-slum areas in Dhaka and Chattogram between October last year and February this year.
The overall adjusted seroprevalence was 68% in the two cities including slum and non-slum people, researchers said Tuesday at a programme jointly organised by Bangladesh Health Watch and icddr,b.
"A lot of people got infected by Covid-19 without showing any symptoms. As a result, they have developed the seropositivity," said Prof Dr Mahmudur Rahman, former director of the Institute of Epidemiology, Disease Control and Research (IEDCR).
Seropositive means an individual has antibodies in the blood against coronavirus. He could have developed it after being infected or exposed to the virus, and his body produced antibodies in response.
"Apart from this study, several earlier researches suggest the similar pattern in slums – that means the slum dwellers were more exposed to the virus," Prof Mahmudur Rahman said.
He, however, noted that further research needs to be conducted to explain the development of seropositivity among the slum people.
Dr Firdausi Qadri, a senior scientist at the icddr,b, termed the findings "encouraging" and said, "It suggests the beginning of a herd immunity."
But Prof Mahmudur Rahman was critical of the assumption. "Herd Immunity varies disease to disease, and it cannot be generalised. Since Covid-19 infection is new, it is not yet known what percentage of the population with antibodies can attain the hard immunity," he commented.
The World Health Organization (WHO) scientists initially estimated that 60%-70% of the population needed to acquire resistance to the coronavirus to banish it.
Researchers at the programme said the youths and physically active individuals in slums are showing exceptional strength against Covid-19 as they rarely got infected or became critically ill.
Referring to the study findings, Prof Mahmudur Rahman said the infection rates are also low among people who are physically active.
But he suggested that there should be more research on low death and Covid-19 severity rates among the low-income people.
Dr ASM Alamgir, principal scientific officer at the IEDCR, said, the virus infection does not vary in rural and urban spaces, or slum and upscale areas. Most slum dwellers are young, and the age dividend could have been the reason for the lower infection rate there.
The researchers said similar studies showed higher prevalence of Covid-19 antibodies among slum dwellers in India's Delhi. But it was found later the antibodies did not last too long. Many low-income people in the neighbouring country could not survive the Covid tsunami as their antibodies wore out quickly.
According to the study, higher seroprevalence was found in less educated individuals, and people with diabetes, overweight, and hypertension.
Inadequate vitamin D status did not show any impact on seropositivity as there was a high rate of vitamin D insufficiency (up to 84.6%) in the population.
Lower seroprevalence was found in individuals who frequently washed hands, did not put fingers on the face, have been vaccinated with BCG, and carried out moderate physical activities.
The study found the seropositivity was similar across adults and children. The seroprevalence was higher in females – up to 70.6% – than in males which was 66%. Among the seropositive participants, only 35.5% were estimated to have mild symptoms.
Don't dump away mask, other safety guidelines
Dr Tahmeed Ahmed, director at the icddr,b, reminded people about wearing face masks, maintaining social distance and other virus safety guidelines.
"If there is fever, cough or breathing issues, it should be assumed as a coronavirus infection, and must be tested immediately," Dr Tahmeed added.
Dr Rubhana Raqib, one of the investigators of the study, said, the policymakers could encourage people for physical exercise, controlling diabetes and overweight by using the study findings.
In October last year, the IEDCR after a similar study claimed that the rate of Covid-19 antibody prevalence among the Dhaka slum people was 74%. But researchers later said the finding was not "a representational scenario of the metropolitan area".