Experts are currently assessing why Covid-19 case load in Kerala has been far greater than any other state in India. The average number of daily new cases reached a low of 11,000 around the last week of June, 2021, and it has since been rising, albeit slowly. At the same time, the number of cases elsewhere in the country has been falling after a major second-wave peak in the first week of May.
The average daily new cases in the country is at about 39,000 and Kerala currently accounts for close to 50% of all active cases. So, the dominant narrative in the public discourse is that Kerala has failed to contain its Covid epidemic. But is this narrative true? Let us take a look into the official Covid data of Kerala and of India. It’s important to understand that the number of reported infections on any day depends on the effectiveness of surveillance, through tracking, tracing and testing. As there is a huge variability in these factors across different states, it would be unfair to make a straightforward comparison of reported cases in each state, or that of Kerala, against India.
One way to assess the extent of infection spread is to check for the presence of antibodies against the virus through seroprevalence surveys. The Indian Council of Medical Research (ICMR) has thus far performed four nationwide seroprevalence surveys at different intervals. The preliminary results from the fourth round of the survey indicate that the seroprevalence for all of India is 67.6% while that of Kerala is 42.7% – a difference of 25 percentage points. In fact, one can see that the seroprevalence has consistently been far lower in Kerala compared to the national average over all four surveys.
Since the survey sample included both vaccinated and unvaccinated persons, some of these antibody prevalence could also be attributed to vaccine induced antibodies. In fact, at the national level, the seroprevalence only among the unvaccinated was estimated at 62.3%. At the time of completion of the survey in May 20201, about 12% population at the national level and 20% population in Kerala had received at least a single dose of vaccine.
Assuming that the sero prevalence survey reasonably approximates the true extent of the spread of cases in a given population, we can compare the estimated cases against the actual reported cases for both Kerala and India. We can see that the testing strategy Kerala has used was able to detect one in every six cases while the same at the national level was one in 33 cases.
However, using the third ICMR survey results (there were no vaccinations at the time) the under-counting factor was 5.4 and 28 for Kerala and India, respectively. So it is reasonable to say that Kerala’s tracking and tracing system along with its testing strategy has been able to identify at least one out of every six cases – while at the national level, only about one in 30 cases were detected. Clearly, a better rate of detection of cases is a result of better and more efficient surveillance.
It is understood that testing after better tracing and tracking would make the process more effective. Targeted testing may result in a higher test positivity rate (TPR), but it is also cost-effective use of testing infrastructure. Kerala has not only conducted more than double the number of tests per million as the national average, it also has a much better case detection rate.
Thus far, Kerala’s tests have detected 9.2% of its population as being Covid positive, while India did 2.3%. The total testing per million population in Kerala so far has been 2.2-times the national average. It may be also noted that only about 35% of the total tests done in Kerala thus far has been RT-PCR, while the same number is about 48% in India.
Irrespective of the test type used, however, it is evident that Kerala’s testing strategy has so far been more effective compared to the national average in detecting a higher proportion of cases. The state has also fully vaccinated 16% of its population while India has vaccinated 6.8%.
Then why are Covid case numbers in Kerala still not falling? The simple answer is that: Kerala still has a larger fraction of population that is unexposed to the virus, compared to all of India. While Kerala has about 50% of its population still susceptible to the novel coronavirus, the same is only about 30% in India. Clearly, the vulnerable population as a percentage of the total population is much higher in Kerala. This is despite the fact that the very first Covid case in India was reported from Kerala.
