We had earlier published in these columns a method of identifying the momentum peak and the numerical peak of the second wave of the Covid epidemic in India, its States and districts in each State. We had made available an online link for District administrations and health department to quickly assess the status of the epidemic with respect to the momentum, numerical peak, active cases peak, mortality acceleration peak and the numerical mortality peak in each district. We present the status of the epidemic in each district in Tamil Nadu and the implications of this analysis for planning.
The three peaks we illustrate in this article are the momentum peak, the numerical peak and the active cases peak; they consistently occur sequentially in this order with intervals of several days between each peak. However there is clear asynchrony in the timing of these peaks in different districts underscoring the importance of epidemic management in each district depending upon the status of the epidemic dynamics in that district. The two graphs illustrate the dynamics in Chennai and Coimbatore districts.
The momentum peak represents the time of peak spread of the epidemic and indicates that the numerical peak will follow in the next few days. If biological and social vaccines are effectively deployed before this peak, contagion can be retarded, providing time for health care system to enhance facilities and cope with the patient load. The numerical peak is the point after which the numbers of new cases show progressive decline.
This is followed a few days later by the peak of active cases. This more or less coincides with mortality acceleration peak in each district and indicates the date on which the given district has the largest average number of active cases during the second wave - the time point beyond which the average active case number will steadily decline.
The number of active cases on any given day is a key determinant of the number of new cases. When active cases decline, there will be a progressive decrease in the average daily number of new cases. However, in districts which have passed the active case peak, the daily count of severe infections and death will continue to increase for the next 1-2 weeks because of the time lag between infection and death.
Districts in Tamil Nadu can be classified according to whether they have reached all 3 peaks, or first two peaks or only the momentum peak, as presented in the Table. Typical examples are shown in the three graphs.
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We can categorize districts into 1) those which have completed the 3 peaks and are then on the decline of the third peak, 2) those which have completed 2 peaks but are yet to reach the third peak and 3) districts which have only completed one peak wherein the other two peaks have not occurred yet.
What are the implications of this classification?
Districts which have just crossed all three peaks (19 out of 37) should anticipate maximum sick patients who need admission to hospital within the next 1-2 weeks; they should focus on augmenting their supplies of oxygen, essential drugs and intensive care beds. They should ensure that Covid appropriate behaviour is strictly followed by everyone but can relax lockdown as the daily new cases will continue to decline steadily. In this situation the economic harm due to lockdown will outweigh the benefits in terms of reducing disease transmission.
Districts which have crossed only the first two peaks (7 out of 37) should be similarly prepared and in addition should continue active case finding through syndromic approach and testing for coronavirus infection. The lockdown restrictions should be continued till numerical peak is reached. Districts which have crossed only the momentum peak (11 out of 37) should be prepared to handle increasing number of new cases over the next several days till the numerical peak is reached.
In these districts lockdown restrictions should be strictly continued till the numerical peak is reached. These districts which still have a substantial proportion of vulnerable individuals, should, in addition, pursue an aggressive vaccination campaign and enforce strict adherence to the social vaccine concept (wearing a fitting mask, avoiding crowds, maintaining physical distance, cough etiquette and frequent hand-washing) to protect the susceptible population from getting infected. Such a stream-lined approach will be the correct scientific management of the epidemic at district level.
M S Seshadri is former Professor of Medicine and Clinical Endocrinology, Christian Medical College, Vellore, currently Medical Director, Thirumalai Mission Hospital, Ranipet; Muru Subramani is researcher, Bhaktivedanta Vidhyapitha Research Centre and T Jacob John is former Professor of Clinical Virology, Christian Medical College
What is the momentum peak
The momentum peak represents the time of peak spread of the epidemic and indicates that the numerical peak will follow in the next few days. If biological and social vaccines are effectively deployed before this peak, contagion can be retarded, providing time for health care system to enhance facilities and cope with the patient load
