IEDCR Survey on Covid-19: Herd immunity in some city areas?

The epidemiological study, which found 45 percent of the respondents in the capital to be carrying Covid-19 antibody, indicates that residents in some parts of the city may have developed herd immunity, say experts.

Noting that the sample size of the study does not represent the entire population of the city, they say the study reinforces the necessity for maintaining health safety guidelines as it showed the majority of the infected people had no symptoms.

The findings of the study carry a lot of importance and will be helpful in transmission control, treatment of the infected people and also vaccination, a number of experts told The Daily Star in their reactions to the first ever cross-sectional epidemiological survey in the country.

"The sample size is not representational. It can be said, but not surely, that some pockets such as slums may be approaching herd immunity. We need to conduct further study with a representative number of samples to know the reality," noted virologist Prof Nazrul Islam told this newspaper.

The study, jointly conducted by the Institute of Epidemiology, Disease Control and Research (IEDCR), and the International Centre for Diarrhoeal Disease Research, Bangladesh (icddr,b) also found that 74 percent of the slum dwellers were carrying Covid-19 antibody during the survey.

A total of 125 samples of individuals in slums and 692 samples of individuals from other areas in 25 wards of the city were tested for Covid-19 antibody under the study supported by the Bill and Melinda Gates Foundation and the USAID.

Researchers involved in the study said the findings do not imply that there should be any change in Covid-19 transmission control and prevention activities.

"Herd Immunity does not depend on a single aspect. The World Health Organisation is also suggesting that we should not think too much about herd immunity because it depends on many things. We have not yet been able to carry out any thorough study," Prof Tahmina Shirin, director of the IEDCR, told this newspaper yesterday.

She said there was nothing in the study which implied that there should be any change in the existing health safety rules.

Expressing similar view, Prof Nazrul said there is no alternative to enforcement of the health safety rules such as wearing masks, maintaining physical distance, and washing hands.

Herd immunity occurs when a large portion of a community becomes immune to a disease through vaccinations or mass spread of a disease.

Prof Mushtuq Hussain, a consultant for the IEDCR, said, "The study showed that the majority of the infected people had no symptoms, and of them, 18 percent were children. This is why the educational institutions cannot reopen.

"The survey does not necessarily represent the whole picture… Based on this survey, it is not possible to reach any conclusion about herd immunity," he pointed out.

"A big portion of the population has not been infected yet. And those who have already been infected should not think they are safe because different studies show that antibody sustains in a human body for a maximum of three months."

Antibody is a kind of blood protein produced in response to a specific antigen. It counteracts the antigen, and can prevent viruses from causing infections by binding, neutralising or making those inactive.

In case of Covid-19, there are two major types of antibodies -- one is the IgM that can last for a few days in the body and the other is the IgG which can last up to three months.

The findings came at a time when Prime Minister Sheikh Hasina warned of a second wave of the novel coronavirus. A number of countries have already been hit by a second wave of the virus.