Coronavirus Explainer: What Is A Sero Survey And Why Is It Important In The Fight Against COVID-19?

New Delhi: One in five Indians have had COVID-19 reveals a latest sero survey conducted by the Indian Council of Medical Research (ICMR). The ICMR survey found the sero prevalence at 21.5 per cent of India’s population. This means, around 29 crore people in the country have been infected with COVID-19 compared to the confirmed 1.07 crore cases. This is the third sero survey carried out by ICMR since the start of the COVID-19 pandemic and was conducted between December 7, 2020 and January 8, 2021. So, what is a sero survey and why is it important in the fight against the COVID-19 pandemic.

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What Is A Sero Survey?

Sero studies popularly known as sero survey examines how many people in a population have been infected with COVID-19 and recovered from the same. It is done to gauge the prevalence of the virus in a particular area.

How Is A Sero Survey Done?

The blood serum of a group of individuals is tested using an antibody test, also known as a serology test. It examines if an individual’s immune system – body’s defence against illness – has responded to the infection.

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In one of the media briefings, Dr S.K. Singh, Director of National Centre for Disease Control (NCDC) had explained the two kinds of antibodies – IgM (Immunoglobulin M) and IgG (Immunoglobulin G). He said,

IgM antibody indicates the presence of active COVID-19 infection and starts getting positive after a week of contracting the virus. But since IgM disappears soon, it does not give a clear p oficture of total exposure. On the other hand, IgG antibody develops after two weeks of the onset of the infection and remains in the body for a sustained and longer period.

#IndiaFightsCorona:

IgM antibody indicates presence of active #COVID19 infection, but it does not give a clear picture of total exposure. However, IgG antibody remains in the body for a sustained and longer period: @Director_NCDC briefing

#IndiaWillWin #StaySafe @ICMRDELHI pic.twitter.com/icLgdr5CDb

— #IndiaFightsCorona (@COVIDNewsByMIB) July 21, 2020

A sample of a population is selected that represents the trends. For the third national sero survey done by ICMR, a sample of over 28,000 (28,589) people aged 18 and above were selected. Blood samples of over 7,000 healthcare workers were also collected and the sero prevalence was found to be 25.7 per cent. The survey was conducted in the same 700 villages or wards in 70 districts in 21 states selected during the first and second rounds of the national serosurvey.

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What Is The Importance Of Sero Survey?

In a conversation with NDTV, Dr. Jyotismita Pathak, Assistant Professor at Army College Of Medical Sciences in Delhi explained the role of sero survey. Dr Pathak said,

Iceberg has a visible section which floats above the waterline, however, there is a larger, invisible section sub-merged in the water. Similarly, in the case of any infectious disease, we get to know about the cases that are reported; like, the COVID-19 numbers you see on state and national health portal. But there are cases that don’t come to notice for various reasons – they are asymptomatic, or people didn’t report. So, a sero-survey focusses on that sub-merged portion of the iceberg and tells us what the infection to case ratio is.

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Sero survey essentially gives a rough idea of the population exposed to the virus. To win a battle against COVID-19, experts are also talking about developing herd immunity – a uniform amount of immunity that at least 60 to 70 per cent of the population in a community must develop to slow down the spread of infection. According to Dr. Pathak, a sero-survey also helps in knowing what percentage of a population has developed immunity against the virus and how far are we from herd immunity.

According to WHO’s Chief Scientist, Dr Soumya Swaminathan, sero surveys can also help look at which groups are more exposed or have had higher rates of infection. She explained,

If you include health care workers, children, other kinds of frontline workers, the elderly, you start getting an idea of who is more exposed, who has been less exposed, where have the infections being the most. You can also look at, the localities within cities. So, for example, you could look at low income, highly crowded, urban settlements versus rural areas, for example, to see if there’s a difference in exposure. And then finally, if you do these tests repeatedly, these surveys repeatedly over a period of time, the authorities, the local public health authorities get an idea of how infection rates are progressing in that particular area.

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What Is The Role Of Sero Positive People?

Most transmission happens between the people. The sero positive people break the chain of transmission because they have immunity. This is what leads to the much talked about herd immunity altogether.

For How Long The Immune Response Lasts?

According to various studies, the immunity lasts for four to six months but other kinds of immune response like T cells or T-lymphocytes may prevail for a longer period of time. T cells are memory cells that remember the antigen or virus for a longer time and recognise the virus if it enters the human body second time and activate a response. If an individual is reinfected with Novel Coronavirus, he/she/they might not develop the disease, courtesy T-cell immunity. This means, one might catch the virus but T cells won’t allow the virus to multiply enough in your body to cause the disease.

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NDTV – Dettol Banega Swasth India campaign is an extension of the five-year-old Banega Swachh India initiative helmed by Campaign Ambassador Amitabh Bachchan. It aims to spread awareness about critical health issues facing the country. In wake of the current COVID-19 pandemic, the need for WASH (Water, Sanitation and Hygiene) is reaffirmed as handwashing is one of the ways to prevent Coronavirus infection and other diseases. The campaign highlights the importance of nutrition and healthcare for women and children to prevent maternal and child mortality, fight malnutrition, stunting, wasting, anaemia and disease prevention through vaccines. Importance of programmes like Public Distribution System (PDS), Mid-day Meal Scheme, POSHAN Abhiyan and the role of Aganwadis and ASHA workers are also covered. Only a Swachh or clean India where toilets are used and open defecation free (ODF) status achieved as part of the Swachh Bharat Abhiyan launched by Prime Minister Narendra Modi in 2014, can eradicate diseases like diahorrea and become a Swasth or healthy India. The campaign will continue to cover issues like air pollution, waste management, plastic ban, manual scavenging and sanitation workers and menstrual hygiene.