What has led to drop in Covid-19 cases in India

NEW DELHI: India registered 18,088 new coronavirus cases on Wednesday. The number of coronavirus cases in the country have remained below 20,000 since January 2. These are the lowest figures of coronavirus cases in the country in the last six months.
Cases have been consistently decreasing since mid September when over 97,000 cases were reported in a single day.
The daily new cases have seen a fall of over 80% since September.

The downward trend in cases is being attributed to 'localised' herd immunity in some of the hardest-hit areas of the country.
Fall in testing not proportionate to fall in cases
There has been a slight reduction in daily testing in the last couple of months. However, the testing figures have remained above the 800,000 mark.

In September-October, over a million tests per day were being conducted. The last time a million tests were conducted was on November 29.
It is evident that the drop in testing is not proportionate to the drop in the number of cases.
One of the lowest test positivity rates since the start of pandemic
From a high of 11.2%, the positivity rate has come down to less than 2% in January. The positivity rate is the percentage of all coronavirus tests performed that are actually positive.

The World Health Organisation recommends a threshold of 5% for positivity rate. Anything over 5%, is considered too high. It indicates that the virus is either spreading too fast, or the number of tests is not adequate.
The low value of positivity rate indicates that the virus is abating and the worst phase of the pandemic is likely to be over.
Cases falling in worst-affected states as well
Similar trends have been observed in some of the worst-affected states. Barring a slight spike in cases in November, cases in Maharashtra have been falling since mid-September.
In Delhi, the only region to witness three peaks of coronavirus, cases have been coming down since November.
The southern state of Kerala too appears to be getting a grip on the virus after an exponential surge in cases in September and October.
Similar fall in cases was observed in Uttar Pradesh, Karnataka, Tamil Nadu, Telangana and Andhra Pradesh.
New cases not rising in worst-hit districts
In 15 worst coronavirus-hit districts (mostly urban), the new cases have remained consistent in the last three months, according to a State Bank of India report.

From August to September, the share of new cases in these districts registered a fall. The fall can be attributed to pandemic spreading to newer zones away from the hotspots.
Localised herd immunity
Experts attribute the fall in the number of cases to localised herd immunity.
Herd immunity develops when a sufficient number of people within the community develop immunity against the virus. The virus, which is passed on from person to person, fails to find a sufficient number of people to infect and hence, its growth rate falters.
Experts say that as many as 50-90% of the population needs immunity to develop herd immunity in a country.
"While the actual numbers may well be underestimated, the trend of lower numbers appears to be real and the rate of spread of the infection is likely to have reduced," said immunologist Satyajit Rath.
The crowded urban localities and neighbourhoods where spread was very rapid earlier might be largely saturated, a form of hyperlocal 'herd immunity', Rath, from New Delhi's National Institute of Immunology, said.
The lack of more travel and the distancing measures — however poorly implemented — may be keeping rates of spread somewhat lower in other less crowded neighbourhoods, he said.
Given a large number of infections in the first wave, it is certainly conceivable that some population immunity has set in and it is difficult for the virus to transmit as easily as it had in the first round, said epidemiologist and economist Ramanan Laxminarayan.
Shahid Jameel, director, Trivedi School of Biosciences, Ashoka University said that while it is unclear what per cent infection or exposure is needed for herd immunity for Covid-19, most epidemiologists believe it would be 60% or above.
If that be the case, we may be closer to it in some but not all locations, Jameel added.
Considering that we went through two important periods without any significant upturn (Dussehra to Diwali festive season and Bihar elections), I think that there would be enough infected people and we will not see a second wave, said the virologist.
Death rate has also fallen
On Wednesday, the death toll from the virus crossed 150,000 mark. The last 25,000 deaths were reported in 60 days — the second-longest time since the outbreak of virus. It took 126 days for the first 25,000 deaths during the beginning of the pandemic. September was the worst-hit month when 25,000 deaths were reported in 23 days.
Since December 25, barring January 1 when 414 deaths were reported, the number of fatalities have remained below 300.

However, the case fatality rate, which measures the number of daily deaths against daily confirmed cases, has remained consistent.
Fatality rate in 15 worst-hit districts stagnant

The 15 worst-hit districts were contributing over 3% of the total deaths in the country during the beginning of the pandemic. In the last three months, the percentage share of fatalities has remained nearly stagnant in these districts, according to the SBI report.
(WIth inputs from agencies)