Results of withheld sero survey expose a ‘lost chance’


1.10 lakh people could have been infected in May-end and proper intervention might have helped detect more cases early

After a lag of three months, Kerala has released the report of the baseline sero surveillance study it did in June, piggybacking on Indian Council of Medical Research’s report of the second round of sero survey conducted in the State in August as part of a national survey.

Despite the alleged shortcomings in the study, the fact that nothing was done to analyse the data and put it to practical use can be seen as a lost opportunity to check the spread of COVID-19, public health experts say.

Study abandoned

The study was done in 9,483 individuals using rapid antibody kits during June 8-14 to find out baseline sero prevalence in the community and determine the proportion of the population which had prior silent exposure to the SARS-CoV-2 virus. However, the study was abandoned by the Health Department after the first round itself following problems with the test kits.

The report now released says the proportion of IgG positivity (indicative of silent prior exposure to SARS-CoV-2) was high amongst those in institutional quarantine (19%), home quarantine (6%) and expatriates (5%). Eliminating these groups, the proportion of IgG positivity was between 0.2 and 0.5%. IgG positivity in samples from the elderly and epidemiological samples together was 0.38%. Among health-care workers, it was 0.5% (COVID and non-COVID hospitals). It also detected 13 cases of active infection (reconfirmed by reverse transcription-polymerase chain reaction, RT-PCR) from amongst those tested IgM positive.

Same as ICMR stats

The report says IgG positivity in non-exposed groups, which means the general community, was consistent with the data from the first round of the ICMR sero surveillance done during May 18-23, which put the IgG positivity at 0.33%.

Going by the State’s (and ICMR’s) estimate of 0.33% of past infection in May, when extrapolated to the State’s population of 3.34 crore would translate to 1,10,240 infected individuals. The actual cases detected in Kerala then were less than 1,000.

Though a chunk of the individuals would be asymptomatic and would defy detection, they would still transmit the infection. But the narrative at the time was about how the State had COVID-19 under control.

That 0.5% of health-care workers in both COVID and non-COVID hospitals had prior exposure to COVID was another indicator that infection was actively being transmitted in the community, brought into hospitals by patients.

Second round

“The ICMR’s second round of study done in the same districts during August 24-26 found IgG positivity to have gone up to 0.8%. This would translate to 2,67,250 infected individuals in the general population, when on August 10 the detected cases was only 35,515.

“Had the State kept the sero survey data in perspective and invested in more RT-PCR testing and in better distribution of testing sites, more cases could have been picked up early,” a senior public health professional said.



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