Kerala sero survey. Kerala orders own seroprevalence survey next month

Kerala has decided to carry out a seroprevalence study of its own following the surge in Covid-19 infections after the second wave hit the State during May and June and in the context of public behaviour, mobility and other factors changing with various stages of easing of restrictions.

BusinessLine had first reported on the development on Thursday last, quoting highly placed sources who had indicated that the proceedings could begin during this month itself, pending completion of training session for the field and staff. The survey is now expected to begin during the next month (September).

Wider selection of samples

It will collect samples from the general population, slum-dwellers, children, and pregnant women, among others, said the source. Data collection may not need much time since Kerala has a very good infrastructure and time-tested methodology. It was just a question of identifying the personnel with a target to cover individuals and houses in an area and giving them proper training.

The study will be taken up in the first or second week of September once the district-level training and logistics issues are finalised. After the fourth round of national level survey, the Indian Council of Medical Research (ICMR) had directed States do their own surveys to get a regional assessment.

ICMR national survey

The ICMR survey had reported that antibodies had been detected in just 42.7 per cent of the State's population. But the survey had been done in just three districts (Ernakulam, Palakkad and Thrissur) with around 400 plus samples each, which critics said did not reflect the actual spread in the State.

The State-level survey will draw 4,470 samples from the general population above 18 years; 2,575 from antenatal women; 1,520 from children aged five to 17 years; 1,710 from the tribal population; 1,800 each from the coastal population urban slum communities, adding up to a total of 13,875.

The protocol for the seroprevalence study has been developed keeping in view both methodological as well as operational feasibility considerations, an order issued late on Friday said.

Primary survey objectives

Primary objectives of the study will be to estimate the seroprevalence of SARS CoV-2 IgG antibodies among 18+ age group, antenatal women attending antenatal care clinics, children aged five to 17 years, tribal population of age 18 and above in the rural and coastal areas and slums.

The survey will also help assess the determinants of seropositivity among the studied population; the seropositivity among the vaccinated in these groups and to estimate the case-infection ratio and infection fatality ratio in the general population, the government order said.

Two types of kits

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.

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