Sero survey across all districts in Sept.

To estimate prevalence of SARS-CoV-2 antibodies in community

Kerala will do a seroprevalence study across all districts to estimate the prevalence of SARS-CoV-2 antibodies in the community, which will give an indication of the proportion of the population which has had prior, silent exposure to the virus.

The study will be taken up in the first or second week of September, as soon as the district-level training and logistics issues are finalised, senior health officials said.

The seroprevalence study (measuring SARS-CoV-2 antibody level in blood samples) will help assess the level of herd immunity in the population, derived either through natural infection or through vaccination, and give insights into the dynamics of the pandemic.

It will help the State identify populations or geographic locales where the virus penetration is low and evolve future strategies for disease prevention and control.

The fourth round of national-level sero survey done by the ICMR had reported that SARS-CoV-2 antibodies had been detected in just 42.7% of the population in the State. However, as this was a survey to get national-level estimates, the survey had been done in just three districts (Ernakulam, Palakkad and Thrissur) with around 400 plus samples each.

The ICMR had directed that the States do their own surveys to get a regional estimation of seroprevalence.

Study protocol

The seroprevalence study planned by the State proposes to study the presence of SARS-CoV-2 IgG antibodies in the general population above 18 years (total of 4,470 samples) as well as in specific population groups such as antenatal women (2,575), children aged 5-17 years (1,520), tribal population (1,710), coastal folk (1,800), urban slum communities (1,800).

The total sample size thus comes to 13,875.

The survey will also help in studying the determinants of seropositivity among the study populations; the seropositivity amongst the vaccinated in these groups and in estimating the case-infection ratio and infection fatality ratio in the general population, according to a GO.

The State will use for its survey the same antibody testing kits which were used by the ICMR for its sero survey.

All blood samples will be tested for antibodies using Chemiluminescent immunoassay technology using two kits: SARS-CoV-2 IgG S1 RBD antibodies (Siemens assay) and SARS-CoV-2 IgG Nucleocapsid antibodies (Abbott assay).

Two kits have become necessary as the population has been administered two vaccines- Covishield, which targets the virus’s spike protein to generate an immune response, and Covaxin, which is a whole inactivated virus vaccine that produces antibodies against both S and N proteins.

The Additional Director (PH) and the Director, State Public Health Laboratory, Thiruvananthapuram, will supervise the sero survey activity.

The district surveillance officers and the sero survey nodal officers will implement the activity with the laboratories in their respective district.

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