COVID-19 mortality rate lower in second wave, but correlation between vaccination and mortality rate unclear

One of the silver linings of the second wave of the COVID-19 so far has been the low mortality rate as compared to the first wave of coronavirus cases. However, it may be too early to conclude that the low mortality is due to the nationwide immunisation drive that started in January 2021, or that opening up vaccines from 1 May to those above the age of 18 could mitigate the human cost of the pandemic.

A comparison of the COVID-19 mortality rate, infection rate (or COVID-19 incident rate in percentage) and the vaccination rate shows no correlation among the three, except that as we had stated in our last study of COVID-19 data, while the infection rate has been rising, the mortality rate has been falling. The change appears to be faster in both indicators since mid-March. However, the trend may not continue as a comparison of fortnightly changes in both indicators throws up a completely different picture.

While the fortnightly fall in mortality rate was almost negligible till 8 March, suddenly it fell by 200 percent on 22 March, then lost another 133.3 percent on 5 April and then 71.4 percent on 19 April. In other words, during that period the mortality rate fell from 1.4 on 8 March to 1.37 on 22 March, then to 1.3 on 5 April and to 1.18 as on 19 April.

The sudden fall in mortality rate on 22 March could have been due to the surge in COVID-19 cases. While the number of cases reported in a fortnight nearly doubled between 8 March and 22 March, the fortnightly increase in cases was more than double as on 5 April, while it was more than triple on 19 April.

As more cases rise and given that hospitals across states are already struggling to provide timely care to many, the changes in mortality rate in the next fortnight will be a crucial indicator of the impact of the pandemic even if the mortality rate continues to fall.