For those of you who are mathematically inclined, the spread of a virus follows what is called an asymptotic distribution. It grows exponentially at first and then the rate of growth slows down and the virus dies.Every virus known to mankind follows this distribution.There is a reason for this. A virus is a non-living thing and spreads by invading cells in the human body. But there is a time delay between viral infection of a cell and the time the infected cells begin releasing the virus for transmission. During this period, the vast majority of infected cells are killed by the body’s immune fighting system.So a virus starts its journey by attacking weak immune systems – – the old and unhealthy. It spreads rapidly as it moves from one compromised immune system to another. This is the exponential stage we see in every virus.Viruses being non-living don’t die. They eventually run into increasing numbers of healthier and stronger immune systems and cannot find cells that can help propagate them. When the virus can’t easily find new, susceptible hosts it stops being infectious. And this is the key–IT IS ONLY WHEN THE VIRUS RUNS INTO A LOT OF STRONG IMMUNE SYSTEMS THAT IT STOPS BEING INFECTIOUS. The smallpox virus stopped being infectious when everyone got immunity from it, either directly or through a vaccine.This asymptotic distribution can be seen with the flu virus every year. It starts the season by attacking weak immune systems, grows exponentially for a few weeks and then dies away. This predictable pattern is repeated every year. Everyone knows when its flu season and there are vaccines available, yet it kills 500,000 people every year (WHO statistics).Absent the finding of a vaccine on day 1 of the detection of a virus, there is absolutely NOTHING that can be done to avoid this early exponential growth in infection rates. This is a mathematical reality.The key then to reducing the intensity of the exponential growth phase of the virus is to lower the reproduction number. In other words, by reducing the probability of the virus being able to locate weak compromised cells The best way to do that is through aggressive testing, contact tracing, finding infected cases and isolating the weak and vulnerable. And paradoxically, by letting increasing numbers of healthier and stronger immune systems to come in contact with the virus which eventually reduces its intensity.Every country that has done that has been successful at containing the virus. China, South Korea, Taiwan, Singapore, Hong Kong have tested more people per capita than other countries and have managed to isolate the vulnerable and successfully contain the virus. None of these countries required national lockdowns. Locking down healthy and strong immune systems, the very systems that you need to kill the virus are the wrong thing to do.This is what India needs to do. Acquire as many test kits as possible and randomly test clusters of people (sectors, villages etc). Isolate and lockdown those clusters where the probability of finding infected cases (weak immune systems) is high. But don’t lock down the healthy systems. We need those hundreds of trillions of strong healthy immune cells to fight and kill this virus.There are both health costs and economic costs to this crisis. Both are real and therefore need to be considered. There are seen and unseen costs. The seen are obviously the number of people getting infected and dying. Those numbers are shown by the media every hour and cause alarm.But what remains unseen, especially in a country like India, is the collateral damage from large economic losses–the deaths, suicides, malnutrition, mental health and stress-related problems. Businesses will shut down permanently, people will lose jobs, and there will be massive unemployment and underemployment. These real costs are hard to quantify and so no one thinks about them. Over time they become just statistics. But as happens with most cases, the unseen costs far outweigh the seen costs.Good policymaking should focus both on the immediate and seen health costs, and also the unseen economic costs. India should invest heavily on testing and isolating the infected and those with weak immune systems.Shutting the entire country will not solve the health problems and will only aggravate the economic problems.