NEW DELHI, Sept. 20 -- With coronavirus disease (Covid-19) cases crossing 30 million globally, the appeal of herd immunity as an end to the pandemic becomes increasingly persuasive. Yet, some countries, including India, have recently re-confirmed re-infection using genome sequencing to demonstrate that the second infection was caused by genetically distinct Sars-CoV-2 virus, which has made depending on "a nice big epidemic" - in the words of UK pandemic advisor Graham Medley - to end the public health emergency not just facetious but very stupid....