Three possible ways to end #covid crisis.
1.Drug to cure.
2.Vaccine to prevent
3.Herd Immunity to minimize spread. Let us understand how herd immunity works. For this we need to know about R0 which is the basic reproduction number for the virus. 1/n

R0 refers to how many ppl 1 infected person can spread the virus to during the time he remains infective. So a higher R0 means bad news while an R0 below 1 means spread of virus is controlled. Now we know that the vast majority of #covid patients recover or are asymptomatic. 2/n

These ppl are likely to be immune to further infections,at least for a while.This is true for most viruses but for Covid the duration of the immunity is yet to be determined. So once a person is immune the virus cannot multiply in him as it will be killed off by immune system 3/n

of the body.This prevents virus spread. If in a population, 60% or more are immune then the R0 for the virus will drop to below 1. The virus from an infected person when it goes out will find that more than 1/2 the people it infects are able to kill it off as 4/n

they are already immune. So gradually 1 infected person is not able to pass on the infection to even one other person and gradually the virus dies out. Not fully. There will still be cases but the numbers will be low and manageable. Like we have with H1N1 (swine flu) even now.5/n

So such a population is believed to have got herd immunity to that virus. The commonest way herd immunity is achieved is throiugh vaccination.With #COVID2019 there are 2 issues.We don't know yet whethr ppl develop significant immunity against virus &if we do how long it lasts 6/n

Also with such a killer disease like Covid it is not possible to sit back and allow herd immunity to develop by natural infection without losing hundreds of thousands of lives. That is why the lockdown, to slow the virus spread. Will the lockdown not end virus transmission? 7/n

No it won't. It needs just a few ppl to be transmitting the virus after the lockdown ends to start the spread cycle all over again.This is because the majority of population presumably does not have immunity to this virus as yet.This is what is happening in some countries 8/n

like Singapore & even China that are seeing a 2nd surge. That is why lockdown is NOT the only solution, Unless we know what % of the population is infected and base our easing measures on that we merely postpone the spread of the infection. Thats why countries are doing 9/n

mass testing. They will continue it for the next some months too. Unless you know prevalence of Covid and thus a rough estimate of the immunity of the population it will be tough to make any predictions just based on daily numbers.That is why we could be in for a long haul 10/n

Unless of course we get a vaccine (unlikely for 12 months at least)or a drug very soon, Governments need to prepare plans for at least several months if not a year, both health related and cconomy related. Lockdown has bought us valuable time.We need to use it wisely. 11/11