For a couple of days in a row now, India has reported less than 1 lakh COVID-19 cases in a day, with recoveries outnumbering daily cases. Our vaccine programme, however, continues to remain sluggish with only 3.4% of the population fully vaccinated, and 14.1% having received one dose. A lot has been said about the 'Delta' variant being responsible for the second wave that ravaged the country, and a lot of questions remain about the effectiveness of vaccines against virus mutations. Since December 2019, what have we learnt about our body's response to Sars-CoV-2? Is it possible for the virus to keep mutating and developing "immune escape" properties? Does a "mix and match" strategy of using two different vaccines on a person work? And could we have done better to ensure vaccine equity, especially at a time when supplies seem to be running short? To talk to us about these issues, we have with us today Dr. Satyajit Rath, adjunct professor at the Indian Institute of Science Education and Research, Pune