In numbers: The COVID-19 pandemic

From 0 new COVID-19 cases to 10,000 in six months: dissecting Kerala's second wave

Mask-clad commuters travelling in a ferry in Kochi, Kerala.   | Photo Credit: AP

Kerala brought down the number of new COVID-19 cases to zero on many days in early May, which signalled the end of the first wave in the State. However, after migrants and foreign returnees started coming back and the economy opened up further, a second wave of cases, much bigger than the first wave cancelled out the early success.

(To read more such data stories, subscribe to our weekly data newsletter. Click here to subscribe for free.)

Furthermore, a month into the second wave, local transmission peaked. Lately, the State’s contact tracing mechanism, its strong suit during the first wave, has not been working with the same fervour, with the number of untraceable cases surging.

Two waves

The first wave of cases started early March and ended early May with the peak single-day infections not exceeding 50. The second wave started at around mid-May and is yet to record a peak with the highest single-day infections crossing the 9,000 mark. On October 7, 10,606 new cases were recorded, the highest single-day spike.

The chart depicts daily cases in Kerala.

Charts below appear incomplete? Click to remove AMP mode

Daily case load

image/svg+xml
 

Migrant surge

The second wave can be mostly attributed to the return of migrant workers from other States and returnees from abroad. As of October 4, 10.61 lakh people entered the State through various routes, since the pandemic began. As many as 5,86,059 persons entered via flights alone.

The chart depicts the number of people who returned to the State.

image/svg+xml
 

Local cases rise

After the migrant influx surged in June, for a month, more than 90% of the new cases were imported from outside. But, in July, the situation changed quickly and the share of local infections surged. By the end of July, tables turned, and more than 90% of the new cases were local infections.

97.50% of the new cases recorded on October 4 were local infections.

Imported cases vs local cases

image/svg+xml
 

Unknown cause

Worryingly, the State could not identify the source of a significant number of recent cases. Such untraceable infections have steadily increased in September. Between September 28 and October 4, the State recorded 636 such cases daily on an average. In all, there were 14,120 untraceable cases between August 29 and October 4.

Untraceable cases

image/svg+xml

Inconsistency in tests

While the number of migrants entering the State surged after June, the number of tests conducted was not increased in tandem. The early advantage gained by increasing testing levels in the initial days of the pandemic was lost in June when many positives escaped undetected due to low testing levels.

Post July, the number of daily tests consistently increased, however, the share of positives among them (positivity ratio) also kept increasing. Moreover, over 70% of recent tests were carried out using the Rapid Antigen Detection Method (RADT) method which is not as reliable as the RT-PCR.

Head start

The chart shows the seven-day rolling average of tests per million population since the 10th case in select States.

In the first 24 days after identifying the initial infections, Kerala's test rates were much higher than others. West Bengal's and Bihar's responses were poor initially and continue to be so.

Seven-day rolling average of tests per million

image/svg+xml

Tests shrink

However, after migrants and foreign returnees started coming back, the State did not increase testing adequately. The tests conducted per confirmed case (TPC), which shows whether testing is enough relative to the outbreak size, declined rapidly over time. Testing remained low throughout June.

Kerala was conducting more than 80 tests to identify a positive case in May, which reduced to less than 50 in July. However, Kerala's TPC was still way higher than the Indian average. The State conducted 13 tests to identify one case, as of October 4.

Tests per confirmed case

image/svg+xml

Rising positives

After July, daily tests surged. However, the positivity rate also continued to rise. As the positivity is also rising, Kerala needs to increase its testing levels even more to capture more positives.

New tests per million vs positivity rate

image/svg+xml

Antigen share

Over the past seven days, Kerala did 70% of tests through the RADT method which are less reliable than the RT-PCR tests.

Share of RADT among new tests

image/svg+xml

Rise and rise

About 10.2% of India's COVID-19 cases between October 1 and 6 came from Kerala, a more than three-fold jump from its share in the first half of September. While, Kerala's share in total fatalities continues to remain low, as deaths is a lag indicator, the State might record a rise in the following weeks.

The graphs show % share of cases/deaths (FH=First half, SH=Second half).

% share of Kerala's cases among India's

image/svg+xml