The country is in the grip of an aggressive second wave of the Covid epidemic. The numerical peak of the epidemic was reached on May 6 and since then there has been a consistent decline in the number of new cases. In the absence of wide vaccination coverage, this deceleration and decline can only be attributed to the development of sufficient herd immunity where the effective reproduction number Re (the average number of subjects that a single infected individual can infect at a given point in time) has reached and continues to be < 1. State-wise lockdowns, where appropriately timed, could also have contributed to the decline.
The mortality rates reflected in the number of daily deaths also show similar acceleration and peak followed by deceleration. The mortality peak for India occurred seven days after the momentum peak, indicating that patients are diagnosed late in the course of their coronavirus disease.
However, epidemic momentum and acceleration/deceleration of mortality are asynchronous across individual states in India. Some states, Maharashtra for example, show a decline in the number of new cases per day. And some others like Tamil Nadu and Andhra Pradesh show a continuing increase in the number of new cases.
This asynchrony of the epidemic is also seen in individual districts within states. Our study of the momentum of the epidemic in different districts of Tamil Nadu indicates that there are several that have reached the momentum peak and the momentum has begun to decrease. There are others wherein the epidemic momentum is still on the upswing. Similarly, there is asynchrony in the acceleration/deceleration of the mortality curves too.
Currently, the twin objectives of each district administration are 1) to curb the epidemic where there is rapid spread and 2) enhance healthcare facilities and essential medical supplies, number of hospital and intensive care beds to reduce mortality.
Every district should aggressively promote and ensure Covid-appropriate behaviour by every citizen; promote social vaccine concept (universal wearing of masks, preferably a fitting double mask, maintaining physical distance of at least one metre from others, avoiding crowds, cough etiquette and handwashing after touching objects/surfaces on which droplets/aerosol could have fallen).
They should educate the public about safety and efficacy of Covid vaccines so as to eliminate vaccine hesitancy. This will ensure that both the social vaccine and biological vaccine work in unison and prevent rapid spread of the virus. Every district should also be able to anticipate the events in the natural history of the epidemic, momentum peak, numerical peak and mortality peak so as to take anticipatory steps at the district level.
We have created a set of easy-to-use Microsoft Excel spreadsheets that can be readily downloaded and used by health administrators (from https:/tiny.cc/covid-momentum, follow the readme.txt at this URL for ease of use). At a glance, they can determine the status of the second wave in each district both in terms of momentum of the epidemic and acceleration/deceleration of mortality.
How will this help district administrations? Districts where the momentum of the epidemic is on the increase should adopt aggressive promotion of the social vaccine and ensure everyone wears a mask outside their homes. The risk of intra-familial transmission is much higher in the second wave of the epidemic than it was in the first. Hence wearing masks even inside households is recommended.
Any rapid increase in momentum of the epidemic indicates that a large proportion of the subjects in the district are not yet exposed to the virus and so are susceptible to Covid. A case can therefore be made to considerably enhance vaccination facilities in those districts, particularly to protect the uninfected subjects vulnerable to severe disease and death.
In districts where the momentum peak is over, the administration should anticipate the numerical peak to occur within the next one-two weeks and once it is reached, anticipate the peak in mortality in the next one-two weeks. In these districts it is very likely that a large proportion of the population has already been exposed to the virus and consequently there are fewer susceptible individuals. Anyway with the raging epidemic, vaccination drives in these districts will be difficult to organise—they should take into account the risk of transmission unless crowding is avoided at all contact points including vaccination centres.
Districts that have reached momentum peak and a trend of decline can expect the numerical peak soon. However, mortality will continue and enhanced healthcare must be sustained. Districts that show acceleration of mortality should quickly enhance healthcare facilities and essentials—oxygen, drugs used for treatment like dexamethasone and anticoagulants, hospital beds, critical-care beds—in order to take care of the sick and seriously ill patients with Covid and decrease mortality.
In districts where the mortality curve is showing deceleration, there will be a decrease in the demand for the above-mentioned essentials and they must make preparations to move surplus supplies to needy areas.
Such a streamlined and science-based approach will enhance optimal use of scant resources and reap rich dividends by way of mitigation of the second wave, fewer new infections, greater number of recoveries and fewer deaths from Covid.
Dr. M S Seshadri
(Medical Director, Thirumalai Mission Hospital, Ranipet and former Professor of Medicine and Clinical Endocrinology, CMC, Vellore)
Dr. T Jacob John
(Former professor of Clinical Virology, CMC, Vellore)
Muru Subramani
(Formerly CTO at GlobalScholar, Inc., Bellevue, US, and Research SDE at Microsoft Research, Redmond, US, and currently Researcher, Bhaktivedanta Vidyapitha Research Center, Mumbai)