Each infected Indian could spread it to 4 others: ICMR
NEW DELHI: In the best case scenario, one Indian infected by the new coronavirus (Sars-Cov-2) will infect an average of 1.5 persons but in the worst-case scenario, 4 persons will acquire the infection, a mathematical modeling by Indian Council of Medical Research (ICMR) early in the outbreak has showed.
The calculation determined an epidemiological characteristic known as the reproduction number (also called R-naught and represented often as R0) that determines how quickly an infection is spreading in a population. A value below 1 means the virus is on course to die out, while any number above 2 is difficult to contain without severe interventions. The study “Prudent public health intervention strategies to control the coronavirus disease 2019 transmission in India: A mathematical model-based approach”, however, takes into account data till late February – before India saw its second wave of the outbreak that has now sickened 471 people in the country and led to 9 fatalities.
The report said placing 50% of the symptomatic cases within 3 days under quarantine would reduce the total number of cases by 62% and the peak by 89%.
“The study was done in February when the numbers were not very high; our aim was not to look at how many cases would occur but what methods would work. And lockdown and thermal screening works is what our study shows,” said Dr Raman R Gangakhedkar, epidemiology head, ICMR, and one of the authors of the paper. The paper shows how social distancing will be instrumental in flattening the curve. The mathematical modeling suggests that entry screening of travellers with symptoms suggestive of the coronavirus disease Covid-19 can delay the introduction of the virus into the community by 1-3 weeks.
“Strictly implemented social distancing measures such as home quarantine of symptomatic people, and suspected cases will reduce the overall expected number of cases by 62% and the peak number of cases by 89%, thus “flattening” the curve and providing more opportunities for interventions. These model projections are subject to substantial uncertainty and can be further refined as more needs to be understood about the rate at which infection of this novel virus transmits among susceptible individuals,” the paper said.
In the pessimistic scenario, the basic reproduction number will be 4. In the absence of a licensed vaccine or effective therapeutics, in addition to the non-pharmaceutical measures of hand hygiene and cough etiquettes, quarantine becomes a critical strategy so that cases can be detected early and the chain of transmission be broken to slow down the spread of the outbreak.
“A mathematical model is as good as the data you put in; if the data is robust then you get a good outcome. Since this is a new virus about which we don’t know much there will be limitations but we must understand that it will at least provide us an indicator. Instead of nothing we have something. There is no harm in overdoing something, but we shouldn’t under-do it,” said Dr Lalit Kant, infectious disease expert.
THE ICMR REPORT SAID PLACING 50% OF THE SYMPTOMATIC CASES WITHIN 3 DAYS UNDER QUARANTINE WOULD REDUCE THE TOTAL NUMBER OF CASES BY 62% AND THE PEAK BY 89%