Director of AIIMS Dr Randeep Guleria explains India's vaccine development timeline and says India could have an effective and safe COVID-19 vaccine by the year-end or beginning of the next year. Dr Guleria talks about herd immunity, T-cell immunity and the difference between antigen and RT PCR testing. Dr Guleria also talks about how COVID-19 is manifested in several different types of symptoms and it is no longer believed to be a simple virus but is in fact a "systemic disease".