While Bangladesh is still grappling with getting a real picture of the coronavirus situation in the country, the antibody test could play an important role in detecting if someone has had Covid-19 in the recent past.
As the country detected the first cases in March, there is a possibility that the health authorities could detect a significant number of people who developed antibodies (that do not last for more than three months) and still have it in their system, experts said.
And thus, the data could be used as a Covid-19 surveillance tool as well, they said.
Given the fact Bangladesh has a significant number of mild and asymptomatic cases, nationwide antibody testing could provide useful data for the authorities to make health policies based on information.
Dr Rajiv Chowdhury, associate professor in Global Health Epidemiology, University of Cambridge, UK, thinks the antibody-based serosurvey is an essential public health measure at this moment in Bangladesh to deal with the public health policies.
As per World Health Organization (WHO), serological survey or serosurvey means obtaining specimens from selected populations to test for antibodies to the respective viruses.
Dr Chowdhury said: "It is time to conduct antibody-based serosurveys in Bangladesh since the first case was detected in March, while recent evidence suggests that antibodies developed in response to infection may stay around three months in a recovered patient's blood."
He said national serosurveys, done periodically, can help monitor the trend of population immunity in Bangladesh over time and assess the risk of further localized outbreaks.
"These surveys can also identify people or areas at high risk and guide local immunization policies for vaccine prioritization."
According to the US Centers for Disease Control and Prevention (CDC), an antibody test may not show if an individual has a current Covid-19 infection because it can take 1–3 weeks for his/her body to make antibodies after the infection.
CDC states: "Antibody tests check your blood by looking for antibodies, which may tell you if you had a past infection with the virus that causes Covid-19. Antibodies are proteins that help fight off infections and can provide protection against getting that disease again [immunity]."
Natural herd immunity
Recently, Gabriela Gomes, a professor at the University of Strathclyde in Scotland, authored a paper titled "Individual variation in susceptibility or exposure to SARS-CoV-2 lowers the herd immunity threshold" which estimates if roughly one out of every five people is immune to the virus, it is likely to slow its spread.
As a significant number of people could be asymptomatic in Bangladesh, a nationwide antibody test will show whether Bangladesh has reached that threshold or not.
As for natural herd immunity, Dr Chowdhury told Dhaka Tribune that achieving natural herd immunity without a vaccine is really a problematic concept.
He said there are still uncertainties about the level of immune response and the duration of antibody-mediated immunity for Covid-19 protection among South Asians.
Referring to a large national serosurvey conducted in India recently, one of the worst-hit countries, Dr Chowdhury said the samples taken from the known hotspots such as large metropolitan city of Delhi showed high infection rate (around 25%).
Later on, when all 24,000 samples collected from the entire country were considered together, the infection rate appeared to be only less than 1%.
This shows that a great proportion of Indians in the month of May were still at risk of Covid-19, and the country was a long way from earning herd immunity goals, he added.
In the last week of June, another survey was conducted in Delhi that found a whopping 23.8% of its population might have already been exposed to the virus.
India's National Centre for Disease Control (NCDC) randomly took the blood samples of 21,387 people and tested for antibodies.
Bangladesh needs comprehensive antibody-based serosurvey
Virologist Dr Nazrul Islam told Dhaka Tribune that given the population size of Bangladesh, a huge number of people have to be infected with the virus to achieve natural herd immunity.
However, he thinks it would be a timely and good initiative if the health authorities start conducting a survey to see how many people were infected in the past few months.
He said the major problem is the antibodies are short-lived and there is no evidence so far that a previously infected person cannot catch the virus for a second time.
"Antibodies might give protection for a short, but there is no alternative to a vaccine."
Square Hospitals Ltd, a private hospital in Dhaka, began conducting antibody tests from the beginning of July.
The hospital is running antibody tests to see who are eligible to donate plasma since plasma therapy is one of the more effective methods of treating Covid-19 patients who are in a critical state.
Dr Chowdhury thinks limited private initiatives to do antibody tests can only serve self-referring individual patients, and will provide little or no useful data for the national public health action.
To understand the true extent of viral exposure in the country, Bangladesh needs a comprehensive antibody-based serosurvey including all its districts, such as the ones in India, he said.
"This survey should include a certain number of randomly-selected individuals from each district in Bangladesh to achieve a balance across gender, age, economy, and urban/rural categories," Dr Chowdhury suggested.
"Given Bangladesh's earlier successful nationwide representative surveys on nutritional disorders and other infections, I see no reason why we will not be able to conduct such a vital national survey on Covid-19."
There are also many reliable and cheap point-of-care rapid antibody tests that are becoming available worldwide, he added.
