New Delhi: India’s effective reproduction number ‘R’ for Covid-19 — a key parameter to measure the rate of infection — has increased again this week to 1.17 from 1.11 last week.
This is the second time this month that value has seen an upward trend. The R value went up to 1.19 on 7 July from 1.11 around 26 June, just a week since ‘Unlock 2’ kicked in.
Around 13 July, the R had gone back to 1.11. Now, the R has increased again to 1.17, Sitabhra Sinha, a researcher at the Institute of Mathematical Sciences in Chennai, told ThePrint.
In an earlier interview, Sinha had estimated that with R at 1.19, the number of active cases in India was likely to cross 4 lakh by 19 July.
As of Monday, India had 3,90,459 active coronavirus cases. A total of 11,18,043 people had tested positive for the disease in India, of which 7,00,086 recovered while 27,497 died.
Significance of R
An epidemic is considered to have been arrested when the R value consistently remains below 1. But without continued precautions, it can increase again.
R and R0 (basic reproduction number) are an estimate of the number of people one patient can infect.
R0 is calculated at the beginning of the epidemic when the entire population is assumed to be susceptible to the disease. The ‘R’ changes with time, and takes into account that some individuals are protected from the disease — either because they have developed immunity or because of social distancing and other measures.
For India, R0 was calculated to be about 1.83 in April.
The R0 of a disease depends on three factors — the probability of infection when a susceptible person comes in contact with an infected individual, the average rate of contact between susceptible and infected individuals, and the duration during which an individual spreads the infection.