New Delhi: Recently 62-year-old Dr KK Aggarwal, a former president of the Indian Medical Association and a prominent face of the medical fraternity in the country died after a lengthy battle with COVID. The Padma Shri award winner had been on ventilator support at Delhi’s All India Institute Of Medical Science (AIIMS) hospital for few days before his death. He had taken both doses of the vaccine. Not just Dr KK Aggarwal, there are other doctors as well who succumbed to COVID-19 despite completing the vaccine course of two doses. So, why are people dying of COVID despite both the doses of vaccine? Do the antibodies work against the variants? These and many other questions remain commonly asked in this continued fight against Covid-19. NDTV speaks with experts to understand how antibodies work and how long do they last in the body to provide protection against coronavirus.